· Lynn; Johnny Cash; Don Williams; Marty Robbins; Conway Twitty;RayPrice; and Roy Clark. ON SPECIALISTS ''Let mesay that Ihave sympathy for them, because they're missing the rest

www.americanradiohistory.com


Jim is one of the good ol' boys ofNashville. His engineering career stretchesback some 18years to the days of monomixing. He's done everything from pop to R&Bto disco-and, of course, country Theaviation industry gave Jim his technicalbackground. But he's also prepared himself byplaying four or five different instruments.Some of the names on the other side of theglass from him include Bob Dylan; Simonand Garfunkel; Peter, Paul and Mary; LorettaLynn; Johnny Cash; Don Williams; MartyRobbins; Conway Twitty; Ray Price; andRoy Clark.

ON SPECIALISTS''Let me say that I have sympathy for

them, because they're missing the rest of theworld of music. They're locked into onething and I got it all. I have done fourdifferent styles of music in one day. I did adisco record that got to number six on theBillboard charts, 'Dance With You.'In the sameday, I did a number one country record. Youdon't listen to the same kind of music allthe time. And I don't want to listen to thesame kind of music all the time, either."

ON OVERPRODUCTION"'Swarm.' That's my term for over

production. I've had producers who haveturned and said,'Well, how many tracks havewe got left?' Youmay look at the chartand say, 'Well, we've got nine tracks left.'He'll say, 'Great.' And he looks into thewindow of the studio. 'Hey, let's put anelectric piano on.' Not because the electricpiano fits the song and has a place ormeaning

in the rhythm or in the feel of the song, butit's because he sees one in the room andwe've got nine tracks to go. And that'soverproduction, abuse ofmultitrack recording.And that I don't condone."

ON PLAYBACKS"I actually mix. I don't load tape. I like to

sit down at the console, set my monitor levelsequal and put the band together and get amonitor mix in the control room that soundsas close as I can make it to the record, so thatthe producer and the artist and themusicians can hear and understand whatthey're doing and correct their mistakes.I'm an old mono mixer.And that's what builtmono mixing.''

ON TAPE"A competitor of 3M has stated that 3M

has a greater print-through than their product.It's my opinion that there is no greaterprint-thrnugh on the Scotch®250. It's just notmasked with modulation noise. There alsowas a comment that the competitor's tapewas brighter, when in fact, there was justmore third harmonic distortion in the 10 to 12kc range. I am very stringent on monitoringin the control room. And when I hear asignal off the floor,I want it to come backoff the tape the same way. I don't want itto be embellished with third harmonicdistortion to make it brighter, ormodulation noise to confuse the bass line."

SCOTCH 250WHEN YOU LISTEN FOR A LIVING.



• ls your studio really humming (at 60 or120 Hz)? Are you infinitely baffled bystanding waves? Were you "off the air"for an hour, and no one complained?• You may need help, and next monthwe've got some, as our authors tackle theways and means of getting and keepingyour studio's system and acoustics ingood shape.

• An Audiotronics 26-input Modell IOA Audio Console highlights this soundeffects master control facility. Installedearlier this year at ABC's Broadcast Center on 67th Street in New York, this control room serves two adjacent live effectsand layover studios, as well as providingeffects to twelve TV studios and postnroduction facilities.

THE SOUND ENGINEERINGMAGAZINESEPTEMBER 1980 NUMBER 14, VOLUME 9

31EDITORIALMEASURING THE SOUND OF RADIO I 32

Eric SmallCOMPUTER-INTERFACEABLE EUMIG-1000 I 38

Tom BensenWIRELESS MICROPHONES- I 41

ON STAGE AND IN THE STUDIOJohn Nady

BROADCAST SIGNAL PROCESSING: I 48THE DBX APPROACH

Leslie TylerA db SPECIAL REPORT- I 51

WHAT'S NEW AT THE FCC?John M. Woram

LETTERSI

6DIGITAL AUDIO 12

Barry BlesserTHEORY AND PRACTICE I 18

Norman H. CrowhurstSOUND WITH IMAGES I 24

N. I. WeinstockNEW PRODUCTS AND SERVICES 28

CLASSIFIED 53PEOPLE, PLACES, HAPPENINGS 56

~ is listed in Current Contents: Engineering and Technology

Larry ZidePUBLISHER

Q.O"

(/)('[)

u-('[)3tr('[)....•

Kathy LeeADVERTISING PRODUCTION

Eloise BeachCIRCULATION MANAGER

Lydia AndersonBOOK SALESBob Laurie

ART DIRECTOR

Crescent Art Service GRAPHICS AND LAYOUT

John M. WoramEDITOR

Mark B. WaldsteinASSOCIATE EDITOR

db, the Sound Engineering Magazine (ISSN 0011-7145) i!-. published monthly by Sagamore Publishing Company. lnc . Entirecontentscopyright ' J 980 by Sagamore Publishing Co .. 1120 Old Country Road, Plainview. L.l.. N. Y. J 180.1. Telephone t5 J ól 4.1.1!\5.10. dbis published for those individuals and firms in professional audio-recon.ling. broadcast. audio-visual. sound reinforcement. ccnsultants .video recording, film sound, ele. Application should be made on the subscription form in the rear of each issue. Subscriptions arc$12.00 per year ($24.00 per year outside U.S. Possessions and Mexico: $13.00 per year Canada) in U.S. funds. Single copies are$1.95 each. Editorial. Publishing and Sales Offices: 1120 Old Country Road. Plainview. New York J 18ü:1. Application to mail atControlled Circulation postage rates is pending at Old Saybrook. Connecticut Oó-t75

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And over 55 lines iHctuding:AKG, Ampex. Anrils. Aurotone, Beyer, BGW. DBX,Deltalab. ElectroVoice,Eventide, Gauss, lvie. JBL,Klipsch. Koss,Leader. Lexicon. Master Room, MRLNeumann, Orban, Otari,Revox. Roland, SequentialCircuits. Scotch, Sennheiser. Shure, Sony, SoundWorkshop, Stanton, STL.T.angent. Topeo, Tascam.Teac.Technics,UREI.Vega

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"1)) Lett•M

To THE EDITOR:In John Borwick's article highlighting

British professional equipment manufacturers (June, 1980), the author listedB&W Loudspeakers, but failed to namethe US representative. The representativefor B&W Loudspeakers in the UnitedStates is Anglo American Audio, 1080Bellamy Road North, Scarborough,Ontario, Canada M1H 1H2.

M. J. Remington

To THE EDITOR:We have been reading the letters

regarding broadcast audio processingwith great interest. Here at WMBM wehave taken every step possible to insurethat all dynamic range is eliminated.All music is taped thru two very fast

peak limiters hooked up in series. Thecompression ratio is200 to 1, release timeis 20ms. At this stage we add 15to 20 dBof boost above 5kHz. This is to insureoptimum tape saturation. Phono cartridge tracking force has been optimizedat 0.2 grams; this results in a verypunchy sound to the highs. Our musicis so hot it sounds like the stylus is goingto jump out of the groove.We start our audio chain by chopping

off those annoying highs above 7.5 kHz.A 48 dB-per-octave high-pass filter at150 Hz removes the irritating thumps socommon on today's disco records. Nextthe audio hits our special custom-made27-band compressor featuring over 135adjustments. The discriminating listenerappreciates this attention to spectralconsistency and true loudness. Foil owingthis is the triple-stage hard clipper. Theaudio is clipped so drastically that thealley behind the station is filling up withthe round tops of all the sine waves thatwe clip.The transmitter is two 1kw solid-state

units in parallel to handle the virtual DCmodulation. Special bribe arrangementwith the FCC allows 500% positive peakmodulation.

Listener reaction? Just amazing.WMBM has replaced over 150 speakercones damaged by DC modulation. Lawsuits are pending on 12 auto crashesresulting from listener fatigue. Cume

Index ofAclvertlsenADC 15

10239

42261735254927114620502143222919

. Cover 416296

28714181213

45. 478

.. 52

. . 39

.. 30. Cover 2

10... 24

Agfa-Gevaert . . . . . .American Radio ExpositionAmpex .....Andrews Audio ..Audio EnvironmentsAudio-TechnicaBGWBoseBTXCrownElectro-VoiceESE ....Garner IndustrieslnovonicsJBL .LexiconMcMartin IndustriesR. K. Morrison Blust. Mats.NeptuneNeveOrban .PolylinePro Audio SeattleSescornShure BrothersSPARSSou ndcraftsmenStandard Tape LabStuder RevoxTAD, U.S. Pioneer ElectronicsTelex TurnerTente! .....The Astatic Corp.The Mike Shop3M .URSA MajorVIZ Manufacturing

~~ sales offices

THE SOUND ENGINEERING MAGAZINE

New York1120 Old Country Rd.

Plainview, N Y. 11803 516-433-6530

Roy McDonald Associates, Inc.Dallas

1949 Stemmons Freeway-Suite 670Dallas, Texas 75207 214- 742-2066

Denver14 Inverness Drive E., Bldg. 1-PenthouseEnglewood, Colo. 80112 303-771-8181

Houston6901 Corporate Drive, Suite 210

Houston, Texas 77036 713-988-5005Los Angeles

424 West Colorado St., Suite 201Glendale, Cal. 91204 213-244-8176

PortlandP.O. Box 696

510 South FirstPortland, Oregon 97123 503-640-2011

San Francisco265 Baybridge Office Plaza,

5801 Christie AvenueEmeryville, Cal. 94608 415-653-2122

Karaban/Labiner Inc.New York

25 West 43rd StreetNew York, N.Y. 10036 (212) 840-0660

Chicago333 N. Michigan Ave.

Chicago, Ill. 60601 (312) 236-6345



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Turner desk pagingmicrophones allow the audio professional moreflexibility in choosing the right microphone for each installation.A minimum amount of electronic modification is required becauseTurner hasengineered its products to meet virtually all applications.Twelve distinctly different microphones in two desk-top casestyles.There is a quality Turner desk paging microphone with features tomeet the following applications requirements:• Omnidirectional • Low Impedance • Normally Open Switching• Normally Closed Switching • High Impedance • Zone Paging• Cardioid • Noise Cancelling • Press-To-Talk • Lift-To-Talk• Amplified.And, that's only the beginning. Turner has 13 other paging microphones in gooseneck, handheld and wall mount versions, as wellas a full line of sound reinforcement microphones. Turner doeshave more, and now, with the additional product developmentstrength of Telex Communications, Inc. there will be even moreto come.

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ratings have jumped 350% but quarterhour ratings have dropped unexpectedly.Here at WMBM we are proud to havesolved the audio processing dilemma.

GREG STRICKLANDChief Engineer

db replies:Well done! But couldn't you raiseyour

auto crash ratings a bit? Also, you couldavoid cone damage by soldering a tenpenny nail across each listener '.s terminals. That would real!v take care ofyour quarter-hour problem as well (Nochargefor this advice.)

TO THE EDITOR:Before running out to buy a reel of

two-inch videotape, expecting 5 MHzresponse from your 24-track, consider afew facts of recording life.No direct analog magnetic recording

system is good for reproducing substantially more than a range of tenoctaves. While any properly set upprofessional video machine will recordand reproduce a bandwidth exceeding5 MHz, (greater than eighteeen octaves)demanded by a high resolution colorvideo signal, this is accomplished byfrequency modulating a "carrier" between 7 and 10 MHz, (less than oneoctave). The head-to-tape writing speedrequired to handle this frequency rangeis 1500 ips, accomplished via a rotatingheadwheel carrying four heads. Complexcapstan and head servosystems alongwith various timebase error reductioncircuits help to restore the originalsignal.Now to the tape. The particle orienta

tion for videotape used in this manneris 90 degrees referenced to the tape edge.This works well for the scanning videohead, but tends to destroy the linearity ofany audio tracks recorded the "regularway." The thin coatings, while firmlyattached to the backing, do not lendthemselves to the signal and bias levelsto which audio engineers have becomeaccustomed. This is of no consequencein video, since the FM video signal isrecorded at a levelapproaching saturation.

Helical systems are a slightly differentmatter. Despite Mr. Weinstock's reference to "Helical particle orientation,"SMPTE standards dictate longitudinalalignment-like audiotape-for professional-format helical-scan videotapes.While helical systems offer greatly

improved audio performance whencompared to older VTR audio, thebacking thickness and coating thicknessagain limit the audio signal drives andbias conditions to something Jess thanthose considered optimum in an audioapplication. Reference fluxivity for Cformat audio is lOOnanoWebers/Meter-nearly 8 dB below the level of a"normal" 250 nWb/M audio machine.

While I have disagreed with some ofMr. Weinstock's technical comments, I



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strongly agree with him that we arecrossing into a new period of radioawareness in the field of television, to thebenefit of all of us.

PALMER S. PATTISONAudio EngineerKUED-TV

db replies:Oops! Change the offending sentence

so that it describes superior results (whenrecording audio in videotape), unlessparticle orientation has not been optimized for helical-scanning. This restoresWeinstock 's-and the tape's-originalorienta lion.

To THE EDITOR:I really appreciate the highly technical

articles in your magazine. It's amazingwhat those of us involved in soundengineering can learn from just oneperiodical. Scott Pelking's article in theJuly issue of db on how to build a"PRASP" was just too good to be true.My only complaint is that Mr. Pelkingdidn't say what brand of undershirtworks best for applying stain. However,I checked with several engineers and theconsensus is that Hanes is the best, withFruit-Of-The-Loom a close second.Perhaps you could get Scott to do somemore writing for db. I, for one, wouldenjoy an article about building bookendsor an end-table. Maybe he could evendiscuss whether it is better to use a~-inch or Ys-inchhole when construcinga wren house.

ORIN N. FRIESENChief EngineerKEYN AM&FMLong-Pride Broadcasting, Inc.

db replies:We've always thought that gentlemen

prefer Hanes, although for AC/ DCoperation, you may want to try Fruit-ofthe-loom.

For bookends, why not try aminiaturePRASP? Actually, you'll need two ofthem; one for each side of the book (orbooks). You can also lay a PRASP on itsside, if you need an end-table.As for the birds, that's a little bit

beyond our scope. However, we imagineyou should measure the wrens beforedrilling. But, as a chief engineer, youprobably know all about birdies already.

To THE EDITOR:We would like to take this opportunity

to thank you for the article you did onIndian Creek Recording Studio in yourJune issue. There was however one fact(misprint) which was not correct and isvery important to us and even more so toour clients. Our rates are $100 per hourinstead of the $200 quoted. We feel thatthis is an extemely competitive rate fora studio of this quality.

JOHN ROLLOChief Engineer



J~~[w.¡~~~rt~¡I; ·~·. 'j ,. +;¡; Most horns oftersbrne.cofitrot of ?

¡( the sound pattJmjheY prÓduce.The}¡~~·problem is that;fr'e:ciueljlcie,sat the 1(,, center of the p~tt~[n a~edifferent frof,n"ii~those at the ed~es. ::~ Unless you us~H~ Co;nst~nt ''l]" Directivity horns, /hat'$ the problem!oi you'll have.To the:áudience this mea~s(~ unintelligible, tdo;t}righi, too dull, ;¡~,:,:o ;_ .: :; io,

'i'.".-. and sometimes¡ui.! pl'lin ~..ad'.º. und1¡K ~~::en~:t:~~:J, ÚRCón~tanf' ~~JDirectivity hor!'ls;ffom~.lettro-Voice ,;tj provide full-ran~e_freqÜeoh coverag~.f and effectiveness pf pattern control . '¡- ~' ··~ ~ 'f ~fa;'

"white horns" hasgrown dramaticallyalmost completely by word-of-mouth.Once a sound engineer, musíctanor facility owner hears the differenceHR Const'\lnt Qirectbtity i;r;iakes.a ne,wdemand is created. · e

Ask someone who hasused or héarddl,0'e; sa 1[1{' "'l/> .,,y:,.~

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i-Y.O' +: -'.4/Mdown-to-earth series of papers onthe s~lectioQanq appli~atioQof proJessiétnalPÁ pró~'uctsand éoncepts!1 U.S. Pa\ent Nurpber4q7:.J112 • %1.¡:IV ~:f~Jt·.n~' ~·:,;Wf -~

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BARRY BLESSER

@)Digital Audio

Digital AudioUp to this point in our discussion, we

have considered the encoding processwhere the audio signal passes throughthe anti-aliasing low-pass filter, thesampler and the analog-to-digital converter. The result is a series of digitalnumbers. But now, let's consider thedecoding process, in which this series ofnumbers is converted back into a continuous audio signal. These encoding anddecoding operations are mirror images;each element in the encoder has itscounterpart in the decoder.Just as the analog-to-digital converter

(ADC) transforms a single voltage valueinto a digital word, the digital-to-analogconverter (DAC) transforms the digitalword into a single voltage. Conceptually,the digital-to-analog conversion is muchsimpler, since each digital number

corres ponds exactly to a particularvoltage. In analog-to-digital conversions,there is a quantization error, since arange of voltages within the quantizationinterval are all transformed to a singledigital number. There is no corresponding quantization error in digital-toanalog conversions.

Consider a 10-bit digital word which isto be converted to an analog voltage. The10-bit word specifies one of 1024 different voltages. Thus, the number I mightcorrespond to 0.001 volts, the number2 (0010) to 0.002 volts, the number 3(0011) to 0.0003 volts, etc. Since there are1024 unique voltages, this DAC wouldhave a range of +0.511 to -0.512 in stepsof 0.00 l volts. (The range is asymmetricsince O.O volts is one of the I024 voltages.)

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DE-SAMPLINGWe must now consider the process by

which the individual samples of the DACcan be smoothed to create a continuousaudio sample. This is the reverse of thesampling process in the encoder. At thispoint in our discussion we need todigress, since the way of analyzing thesmoothing processes is different from theway they are actually built. We maythink of the DAC's output as being aseries of samples, as shown in FIGURE IAor, we may think of it as being a constantvoltage between samples, as in FIGUREIB. In both figures, the DAC produces avoltage corresponding to the digitalword. However, in the top figure, theDAC produces its output for a very short"sampling" time. In the bottom figure,the DAC "holds" its voltage until thenext digital word enters to change thevalue. Now, forget FIGURE IB for thetime being and we will return to it lateron.

Since we will be using a low-pass filterto smooth the DAC's output, it would bewise to consider the spectrum of thesignal represented in FIGURE IA. Byunderstanding the spectral content, wecan see clearly how the low-pass filtercreates the desired signal. FIG URE 2shows the way in which the waveform ofFIGURE IA could have been created.FIGURE 2A shows a I kHz audio signal.This will be multiplied by the samplingsignal in FIGURE 2B to create the resultin FIGURE 2C. The sampling signal inFIGURE 2B is a periodic pulse train with a

Figure 1. (A) The sine wave is sampledat regular intervals; (8) each samplevoltage is held until the next sample istaken.

(A)

(8)



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Others could make their heads andmotors aswell, no doubt; they justdon't. Servo-controlled reel torque andcapstan drive (independent of line frequency or voltage) aren't exactly newconcepts. Nor is PROM-logic transportcontrol. But try them all outand seewhether you can settle for anythinglessthan the Studer ABO/RCMk fl.

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Figure 2. (A) A 1kHz audio signal; (8) Thesampling signal; (C) Ax 8 = C.

fundamental at the sampling frequencyand many overtones or higher harmonics. If the fundamental is 40 kHz, wewould expect to find energy at 80 kHz,120 kHz, 160 kHz, etc. Multiplication islike a very severe nonlinearity whichcreates large amounts of sidebands. Thisis similar to amplitude modulation or theintermodulation of two sine waves. Aswith intermodulation distortion, theresulting signal contains frequencies atthe sum and difference of the components. The waveform in FIGURE2C

contains energy at I kHz (audio), 39 kHz(sampling frequency - audio frequency),41 kHz (sampling frequency + audiofrequency), 79 kHz (2 x sampling frequency - audio frequency), 81 kHz (2 xsampling frequency + audio frequency),etc.

SOUND WITHOUT IMAGESThe role of the smoothing filter is to

remove all components other than theI kHz audio. These other componentsare called "images" since the spectracentered at 40 and 80 kHz are the sameas the audio spectrum centered at DC.If the audio signal contains componentsof I00 Hz, 200 Hz and 800 Hz, then thesampled signal will also contain thesecomponents, as well as image components at 40 kHz, 40.1 kHz, 40.2 kHzand 40.8 kHz. There will also be mirrorimages at 39.9 kHz, 39.8 kHz and 39.2kHz. Since the smoothing filter mustremove these images, it is called ananti-image filter.The anti-aliasing filter at the input

limits the energy in the audio to lessthan 20 kHz in this example. But, a19 kHz audio signal produces images at21 kHz [40-19], 59 kHz[40 + 19],61 kHz[2 x 40 - 19] and 99 kHz [2 x 40 + 19].The desired signal at 19 kHz must beseparated from the nearby undesiredimage at 21 kHz. For this reason, it is

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Figure 3. (A) Input and output of alow-pass filter with a very long timeconstant; (8) A low-pass filter with anextra delay inserted; (C) A - 8 = C.

usually better to limit the anti-aliasingfilter to a frequency lower than half thesampling frequency. This provides aguard-band for the transition betwendesired and undesired signals. An 18kHz limit allows a 4 kHz guard band,since the nearest image is now (40 - 18)22 kHz.

SAMPLE-HOLDWe are now in a position to return to

the actual implementation of the DACusing an implied hold. FIGURE IB canbe thought of as holding the samplebetween successive words. We must nowshow that the effective holding action,which turns a very short pulse into alonger rectangular pulse, is nothing morethan a filter. FIGURE 3A shows theinput and output for a low-pass filterwith a very tong time constant, which iscalled an integrator. FIGURE38 showsanother low-pass filter with an extradelay inserted. If these two outputs aresubtracted, as in FIGURE3C, the outputis a pulse. This operation turns thesample pulses of FIGUREIA into the heldpulses of FIGURE IB. Hence, the onlydifferences between them is the filteringproduced by our delay-integratorsubtractor. The implied hold is nothingmore than a filter which has the frequency response given by the equationbelow:

H(f) = sin ( 7rfaTs)7rfaTs

where fa is the audio frequency and Ts isthe sampling period. It is impossible todemonstrate this equation withouthigher mathematics and the readershould consult other references for aproof. The important thing to note is thatthis filtering effect reduces the highfrequencies in the audio band somewhat,and this must be corrected. The filteringeffect of the hold is called the aperture



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>------ ENCODE ____,

AUDIOIN

ANTI-ALIASING AIDLOWPASS SAMPLER CONVERTERFILTER

Figure 4. The complete AID, DIA system.

response. As in photography, theaperture is the size of the opening: pulsewidth. With the pure samples, theaperture is extremely small and there isno effect. A compensation filter must beincluded in the decode process to compensate for the effect when a hold isused. The hold is implied by leaving theDAC on between samples.

GENERATION OF IMAGESLet us return to the subject of the

image frequencies and their origins.The audio signal was said to exist onlybetween DC and half the samplingfrequency. Where then did the imagesignals come from? In the previousarticle we considered the samplingprocess, and showed that it is able tocreate the same sampled signal frommany different input signals. In particular, a 1 kHz sine wave and a 41 kHz sine

,_ DECODE----~~

DIGITAL

AUC>IOOUT

output frequency will still be the sameas the input frequency.

COMPLETE SYSTEMThis completes the introductory dis

cussion on the theory of digital audiosystems. The complete system is shownin FIGURE 4. So far, we have donenothing with the digital word sequenceother than convert it back to audio. Ina real application, the digital sequenceis processed in some interesting fashion,such as delay, reverberation, storage, ortransmission. A digital tape recorderwould record the digital sequence forlater playback; a delay system storesand recalls the sequence. A reverberation system is much more complex, sinceit processes the sequence to create a newdigital sequence.We should also note that the encode

process produces all of the theoreticaldegradation, by the quantization noise ofconversion, and bandlimiting, by theanti-alias filter. The decode processproduces no further degradation, sincethere is no quantization and the antiimage filter is the same as the antialiasing filter. The former removes audiocomponents, whereas the latter removesimages created by sampling.

In the next few articles, we will turnour attention to the actual implementation of the converters. This will introduce us to the real problems of a digital~~fil •

DIACONVERTER

ANTI-IMAGING APERTURELOW-PASS COMPENSATIONFILTER FILTER

The Orban 526A single-channel DyhamicSibilance Controller is a simple, economicaldedicated de-esser-without the complexity ahdcompromises of multi-function processors. It setsup fast to produce sibilance levels that soundnatural and rigt)t. Features include mic/line input,fully balanced input and output, LED level meter,GAIN control, compact size and more. $peciallevel-tracking circuitry assures consistent resultswith varying input levels. And our control techniquedoesn't emphasize residual IM when de-essingoccurs.

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wave, when sampled at 40 kHz, producethe identical result. This is a "mapping"of two (or more) sine waves into the sameresult. The digital number sequencerepresents both sine waves. In fact, thesame sequence represents 1, 39, 41, 79,81, 119, 121kHz. The input anti-aliasingfilter resolves the ambiguity by removing all except 1kHz. However, the digitalnumber sequence does not know thatonly one possible sine wave could haveproduced that sequence. At the output,the decoder produces all sine waveswhich could have created that sequence.We design the anti-image filter to allowonly the one which we know producedthe sequence.

One could have an anti-aliasing filterwith a bandpass from 20 kHz to 40 kHz ifone also has an anti-image filter whichis the same. Such a digitizing system willonly pass those frequencies, but the

De-essing doesn't have to be complex, expensive, apdttime consuming. The 526A does it fast

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NORMAN H. CROWHURST

@)1heory aPracticeVoice Prints and Stress Analysis

What is a voice print? It is an everydayterm for a sound spectrogram of aperson's voice, continuously takenthrough time. Does this mean you canread a voice print? Now that depends on

what you mean by "read." With somepractice, you can recognize patterns thatrepresent specific words and thus, frommemory, you will know those wordsagain on the voice print. But a great deal

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more practice would be needed beforeyou could construct words from yourknowledge of the way sounds go together, rather than by simple recognition.

A SOPHISTICATED "ID"Now, voice prints have been used as a

sophisticated form of identification. Aperson says a name and the machinerecognizes if it's the owner of the name,or someone else, saying it. Only theowner's way of saying it will be acceptedas "authentic" by the machine.Now, think about listening to different

people saying the same name. They allsay it differently, and the voice recognition machine can detect such differences,when compared with a permanent voiceprint of how the person himself says it.But, given that it could tell when you sayyour name, or when I say mine, couldit tell if it was you saying mine, or I sayingyours? Only if those specific voices,saying those specific names, were programmed into it. It could not tell, at thepresent state of the art, merely from priorinputs consisting of each of us sayingour own names.

STRESS ANALYSISThat's a little of what voice prints can

do. Now what about stress analysis?What does a stress analysis machine do?It must work with the same spectralcontent, but process it in a different way.It is not concerned with recognizingthe words you say, but with recognizingwhether you are in a relaxed or tensestate when you say them.

Research has found that subtlechanges in the way the vocal chords workoccur with nervous tension, as comparedwith when the person is relaxed. Whatdoes this mean? A person's voice risesand falls in pitch, some more than others,in the normal course of speech. It may befor emphasis or some other purpose.That, in itself, does not reflect tension orrelaxation. Tension tends to make aperson's voice what you would subjectively describe as "edgy."

How can voice analysis tell that? Notso much by frequency content, as by frequency combination in that content, justas in music. Strident sounds result frominharmonious combinations of tones,while melodic ones result from harmonious combinations. This means thatany such detector must first frequencyanalyze the sound, and then apply theoutput from such analysis to some form





of logic circuitry, that functions on thebasis, not of the frequencies present orabsent, but on the relationship betweenthe frequencies present.

If you are an experienced listener, perhaps you can tell the same thing that avoice stress analyzer can just by listeningto the voice itself, in much the same way amusical conductor assesses the performance of his musicians. Advocates of stressanalyzers, for the most part, want us tobelieve that the machine is "smarter thanthe average ear," with apologies to Yogi.All we can say is that a stress analyzerremoves the result from the subjectiverealm - the opinions of various listeners-to an objective realm-a precise indication on a meter or indicator of somesort.

DON'T JUMP TO CONCLUSIONS!But beware of jumping to the conclu

sion that because the result is objective,it is infallible, as regards determiningwhether the person being analyzed islying or telling the truth. Tain't necessarily so!

First, any machine that will reliablydetect stress, or the absence thereof, in aparticular person's voice, must first becalibrated to that person's voice. Somepeople's voices are more strident whenthey are relaxed than others are whenthey are under tension. This isjust a characteristic difference between individuals,

and is no indication that one person isnormally more tense than another.So, you've calibrated the machine,

using the procedure specified by the manufacturer, and you have tested it by having the subject say something both of youknow to be true, and also something youboth know to be a lie. Good, it indicatesfor this subject. Now, can you be surethe result is reliable?The point to remember is, all it can

really tell you is whether the questionyou ask the subject causes stress. Andstress can definitely be brought on byreasons other than lying. In Victoriantimes, the word "sex," particularly usedin mixed company, would have causedstress. Would the responses achievedindicate that the people present werelying about something? Not necessarily:it would just indicate that a taboo wordhad triggered stress. And there could beother reasons for a similar response, perhaps individual to specific subjects.

IN RELATION TO AUDIOHow does all this affect audio, and

what we may be able to do in the future?It may help to get us thinking about theparameters involved. Perhaps a voicestress analyzer could be adapted to determine whether a specific person, forwhom the device has already been calibrated, or someone else, is speaking in aspecific piece of sound track.

On solo sounds, it would be possibleto modify the same technology to determine what musical instrument is beingplayed, and possibly, even to identify themusician playing it, from somethingequivalent to his "style." But that is stilla long way from being able to isolate sucha sound, in a complex sound channel, obtained from a full orchestra, playing atonce. This is a capability a musical conductor can acquire and maybe, down theroad aways, technology will find a way toduplicate that capability.

DUPLICATING HUMANHEARING ABILITY

So far we can distinguish three basicsystems, with variations, each of whichpartially duplicates an ability of humanhearing. A voice print gives a visualprint-out of any source of sound, as aspectrum of changing frequency contentagainst time. With some skill, which mustbe acquired from working with them, youcan "read" them. You may be able todetect a difference between the voiceprints of different people saying the samething, but you would be hard put toidentify who was speaking, without sucha constraint of having them say the samething.

A second system is based on providingit with an electronic memory, wherebyit can remember the precise voice print

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JBL's new 7510.The automatic mic mixerthat thinks before it speaks.

JBL's new 7510 advanced digital/analog mic mixer actuallythinks before it speaks- by activating or deactivating up to 24input channels. Automatically.Now, you don't need an operatorto constantly adjust controls. The7510 does it all. Quickly, precisely and without error.Versatile modular design rrakesthe 7510 an all-around performer.In churches, meetings, courtrooms and council chambers.Delivered with a single, 4-channel input module, the system isexpandable to 24 channels.. Andeach panel features controls forlevel, threshold, release time andmode selection.The 7510 offers a variety of otheradvantages over conventionalmic mixers. Automatic mic on/off

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Circle 40 on Reader Service Cardwww.americanradiohistory.com


of a particular person saying his ownname, and use that memory to reject theprint of anyone else saying the samename. Data on the precise voice print canbe entered in a magnetic memory on acard, similar to a credit card, which isinserted in the machine, while thepresenter of the card says his name intoa microphone.

Thus, such a machine is a form ofcomparator: it compares the voice printof the freshly spoken word into themicrophone, with the recorded printpresented to it on the card; but it has onlytwo results; go and no-go. If the twomatch, the person is identified. If theydon't, he is rejected as an imposter.

The third kind of machine is the stressanalyzer, often called a "lie detector."This analyzes the prints a little differently.It does not seek identity or non-identity,but rather certain qualities about theprint. To do this, it must in some way be"calibrated" to the individual being"tested," usually by having him statesome already verified fact, which theoperator knows to be true, and thengetting him to say something he knowsto be false. It uses differences about theprint that have been found to be indicative of the state of stress under which theperson speaks.

Because it needs calibrating, it obviously has the basic capability of telling

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the difference between individual voices,although it is not set up to do that, likethe security device is. So all threeduplicate part of human hearing capability. All three start by producing a frequency analysis of sound over time, in aform that could be presented as a voiceprint.

THE AMAZING HUMANHEARING FACULTYThis leads us to conclude that the

human hearing faculty has an infinitelybetter memory system than any of them.We can hear what a person says, and ifwe have heard that voice before, we canalso identify the person saying it. Werecognize words we have heard before,perhaps many thousands of them, andcan interpret them into meanings (rightlyor wrongly). A person transcribing adictated message can "translate" thosesounds into visual symbols, such as thoseyou are now reading.

Efforts are being made to produce areliable transcribing machine. One of themain problems is that of accommodatinga wide variety of different voices, stillrecognizing the same set of words, in alarge enough vocabulary.

Human hearing accepts all signalspicked up by the person's ears, andprocesses them. It has the ability to ignorenon-relevant sounds, according to the waythe person's "listening" faculty programsit, even ignoring sounds that occupy thesarrie frequency spectrum as those beinglistened to, by using pattern recognition.To do this, it must have some way oftelling what frequency components "belong together" as parts of the same sound:the voice of the same person speaking.

How does it filter off-or whateverwould be the appropriate term-justthose elements within the commonspectrum that all the sounds being pickedup are using, and identify them as thatparticular person's voice? To the best ofour knowledge, this is a capability thattechnology has not been able to duplicate,as yet. To do any of the things we havebeen discussing, the machine must beprovided with the sound to be analyzed,pretty well isolated from all other sounds.Does anybody have any answers to this?

•

Copies of dbCopies of all issues of db-TheSound Engineering Magazine starting with the November 1967 issueare now available on 35 mm. microfilm. For further information or toplace your order please write directly to:

University Microfilm, Inc.300 North Zeeb RoadAnn Arbor, Michigan 48106



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@)Sound With Images·Film vs. Video

• American standard television relieson 525 scanning lines of electron dotsto fill a screen anywhere from two inchesdiagonally on up to ten feet and more,if you include the huge projectionsystems used in theaters. The horizontal

resolution of the typical %-inch videosystem is approximately 260 lines incolor and 330 lines in black-and-white.This adds up to about as many bits ofinformation as a fast 16 mm film stock;that is, a film that can be used with

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available natural light. (Film's dynamicrange of bright-light-to-darkness is fargreater than video's, in any formatcompared.)

Much professional film production isdone in.35 mm, creating images with aresolution far better than anything videocan reproduce. Confusingly, for film production done exclusively for showing ontelevision, producers still prefer the35 mm format, even though this difference in quality cannot be reproduced.Why?Could it be the audio portion? (Not

yet a crucial part of the television experience.) Most audio on film is stillrendered (perhaps "rended" is a betterword) in the final product into "opticalsound," the recording device inventedback in the early twenties by Lee DeForest. This capacitance system hasseverely limited dynamic range (about500 to 14,000 Hz), and ages quickly.As the film gets dirty or scratched, whichis inevitable with hard celluloid, you hearit. Historically, film-sound has been sobad that one didn't even mind.the horrorsof "mag stock," or the hard, celluloidbacked, sprocketed, magnetic tape thatwas used to maintain sync with thepictures. The hard backing and sprocketpopping degrades the response, evenbefore the sound gets transferred tooptical. In the 16 mm format, slowtransport speed also contributes its shareof damage.In contemporary film production, the

final sound is often recorded on a "magtrack" instead of optical, particularly inany feature film claiming to have betterthan average stereophonic sound, Dolbysound, etc. Still, the width of each soundstripe involved (0.063 inches) is somewhat thinner than a single track on apro-audio multi-track tape recorder(0.070 inches). (For more on varioussound track formats for film, see theMarch 1980 db-Ed.)Of course, as I pointed out in my last

column, sound on video tape is nobetter, and sound on television is evenworse. Yet, both have high capabilities,and should improve rapidly. For the timebeing, however, quality of both pictureand sound remains on the side of film.But the larger reason why film is usedmore often for programs to be televisedprobably lies with force of habit.Time was, video equipment was all

bulky stuff that did not lend itself tolocation work. Of course, time was thatfilm equipment was zip-locked in thatsame bag. But film broke out of thestudio about 1960, while video is justnow beginning its break-out with smaller,more portable equipment. In fact, withfine video cameras about the same sizeas 35 mm cine cameras, and with thesame degree of lighting needs, and VTRsdown to manageable size, video nowrivals film's convenience factor.And, video has a few added con

veniences of its own. Electronic editinghas just spread to the audio world, and



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most of us are familiar with the incredibleadvance this represents over the age ofthe ragged razor blade and greasy fingers.Film is necessarily still in that ragged age:the editor may use a three-screen, programmable Steenbeck editing bench, butin the end, he physically "cuts theplastic," a step unnecessary in video.In fact, here video's usually-overratedhigher equipment cost is evened out:the hardware to edit video (one editingdeck, controller, processing amp, andperhaps a console) is much cheaper thanthe finest film editing equipment. Without the finest possible editing, film'sadvantage in quality is thrown away. Nota problem with video.

The convenience of the %-inch cassetteshould not be underestimated. On a filmset, there's usually a crew member whosesole job it is to make sure the camera'smagazines are loaded; and those magazines, in 35 mm, won't usually roll formore than twenty minutes. Much moreimportantly, the convenience of seeingwhat you've got on tape as soon as you'vegot it is still something the medium offilm can't match, though Polaroid istrying.

Film and videotape are about equallydifficult to duplicate, but if the film hasa magnetic sound stripe, that's an extrastep-and that takes longer. Speaking ofwhich, it is our understanding that

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another reason mag striping never reallycaught on is that films are still shippedby mail or equally-destructive courierin cans, and are easily demagnetized orremagnetized. Video tape would alsohave this problem, and therefore is a bitless convenient to distribute thanoptically-striped film.But on the distribution end, there is a

psychological factor working in video'sfavor. People are getting used to watching television, and coming to prefer it tositting in a darkened, more formal room.At corporate conferences, sales meetings,in-house teaching, in schools, and indeedin all the domains of the industrial film,the public is coming to demand video,not film. Could this not also represent ageneral belief in video as more technologically advanced?It is, of course. And if films at present

record images with more quality thanvideotape, they record that image as wellas they are ever going to. While advancessuch as the Steadicam, better dollies, andsmaller lights benefit both video and film,the film itself, and its basic hardware, isat the top of its technology. There willnever be better contrast or color represented on film than there is now, and asupportable position in debate is that thefirst Technicolor feature films producedbetter-perhaps more-interesting is theword-color than today's processes.Certainly film and film equipment willnever be more cheap and available thanthey are today.Video may not have the quality of the

best of film just now, but it will in thefuture, for video is at the beginning ofits growth curve. We say "video" advisably, and not "videotape," becausemuch of that growth in quality will comefrom the videodisc, and eventually fromdirect computer storage of information.

Make no mistake about it (here comesthe auspicious pronouncement), thevideodisc represents as much of a superior technology to videotape as magnetictape does to film. (The capacitancerecording, stylus-in-groove, mechanicalsystem soon to be marketed by RCA andits licensees, with all its inherent mechchanical imperfection, and with lousymono sound, is not what we are referringto, and hopefully it will fall by the wayside soon-sorry about that, RCA.) Wespeak of those video systems that use thelaser-probably, more than atomicenergy, the greatest discovery of ourtime. Aside from zapping some futureStarship Enterprise, the laser is therecording apparatus of Philips/ Magnavox's new disc, and provides strikingimprovements in the recording of bothpicture and sound, bringing both up tothe level of the highest quality film anddigital audio.

Next time, we'll get back to solid engineering ground, as we unravel the mysteries of the Time Base Corrector. •



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@)Editorial

NEXT MONTH, the National Radio BroadcastersAssociation holds its annual convention (LosAngeles, Bonaventure Hotel, October 5-8).In honor of the event, we devote this month's

db to a look at various aspects of broadcast audio.Usually, we tend to think of pro' audio as something

that happens in the recording studio. After all, recording engineers are into audio, while broadcast engineersconcern themselves with, well, broadcasting.

Broadcasting what? Why, audio of course; for example, your very next chart-buster: the one that hasn'tgot a chance unless it gets plenty of air play.

After recording, mixing and mastering, your potentialhit record will surely encounter some "we'll fix it afterthe mix," when (and if) it arrives at the broadcast studio.Some stations have their own special "sound," whileothers simply try to be the loudest game in town. Ineither case, your priceless master is in for even moreprocessing, which will hopefully keep those listenerstuned in.

But how much processing? Eric Small has come upwith a means of"modulation analysis" in which he quantifies what goes on just before the transmitter. Usingthe New York marketplace as his guinea pig, he makessome interesting comparisons between stations from hislab, somewhere in the wilds of darkest Brooklyn. Barring an offer he "can't afford to refuse" from some program director, Eric will probably show up in your hometown, as he goes about Measuring the Sound of Radio.

Playing a significant role in the sound of radio is thecelebrated(?) NAB cartridge. Recording engineers, longaccustomed to the relative sophistication of open-reel,may wonder about the continuing popularity of thecartridge system in broadcasting. Elsewhere, the carthas all but disappeared, in favor of cassettes. Why not inbroadcasting?

Why not indeed, asks Eumig USA, Inc. Technicalrepresentative Tom Bensen, who describes the company'smicro-processor-based system, which may be used tocontrol up to 16 cassette decks, using a low-cost personalcomputer. With a little creative imagination, suchcomputer-controlled cassette systems will probably startshowing up outside the broadcast studio as well.

Speaking of outside the broadcast studio (nice segue,huh?), what about wireless transmission inside therecording studio? The wireless microphone has beenaround for some years now, but until recently it has beenregarded as somewhat of a compromise, to be used onlywhen microphone cables are absolutely out-of-thequestion. However, wireless transmission and receptionhas at last come of age, and John Nady offers us an

interesting overview of theory and application, both inand out of the recording studio.

While wireless microphones are finding their way intothe recording studio, noise reduction systems areshowing up outside the traditional studio venues. Dolbyfilm sound comes to mind, and of course there's theDolby 'B' system in consumer audio. Now, dbx isbeginning to make its presence felt in broadcasting, andhas in fact installed a custom-designed noise reductionsystem in National Public Radio's satellite communications system. This month, d bx chief engineer Leslie Tyler,shares with us the dbx approach to broadcast signalprocessing, which naturally includes a look at noisereduction, plus some talk about actually expandingdynamic range.

We close with an inquiry into What's New at the FCC.As you may have heard, there's a recession going on outthere, and its having its effects on all of us.Traditionally,the recording/ broadcast industries have been comparatively "recession-proof," as people stay home moreand therefore spend more time listening to radio andrecords.

Well, this time around, our industry is also feeling thepinch, and it could certainly use a little perking up. Inshort, this would be a good time to see AM stereo andFM quad finally come off the drawing boards. Therecording industry would be revitalized, AM radio wouldcome a lot closer to "hi-fi," and FM would be able tosurpass anything heard to date.

However, first we must contend with the FederalCommunications Commission. The Commissionersrarely act in haste. Some say they rarely act, period. OurSpecial Report will bring you up-to-date on theCommission's most recent contributions to the state-ofthe-art.

In a New York Times (July 20) article entitled "In thePublic Interest. Hah!," Jerome Gillman (WUST-FM)describes his own seven-year battle with the Commission.He concludes with the suggestion that the Commissionmust be re-structured from scratch. The NRBA has sentreprints to all members of Congress, and it asks interestedparties to write directly to their legislators to conveypersonal opinions and experiences in coping with theFCC.

Depending on the results of the November election,there may be some changes at the Commission, as well aselsewhere of course. (Some Washingtonians are alreadybeginning to pack.) And so, this might be as good a timeas any to let your elected representatives know how youfeel. Maybe something good will come of it-but notunless you do your bit. •

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TOM BENSEN

Computer-lnterfaceableEumig FL-1000With all the problems confronted in using an NAB cartridgesystem, why not give cassettes a try?

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IN BROADCAST AUDIO, the NAB cartridge system is by nowa well-established fixture. Therefore, before going into thetechnical details of interfacing a cassette system with amicro-computer for broadcast applications, it might be

wise to answer the question; Why use cassettes in the first place?Quite simply; Why not? The broadcaster has been livingwith

the NAB cartridge for more than 25 years, trying to cope withproblems such as excessive wow and flutter, poor stereoseparation, phase shift and imaging. The graphite-lubricatedtape requires constant maintenance and its residue causesjamming, tape breakage, etc. Because of all of the above, theNAB cartridge also suffers from instability of frequencyresponse.Though advances have been made recently in the NAB

cartridge system, it is still unable to compete with thespecifications of today's cassettes. According to Ed Havens,technical services manager at TDK Electronics, "It is widelyrecognized that more emphasis has been placed upon the audiocassette in the last ten years than any other analog tape medium.Improvements in all areas of their development have elevatedcassettes technically, certainly exceeding those of the NABcartridge, while effectively challenging open-reel recorderspecifications at 7l/i ips. The most significant improvements incassettes are generally noticed in two areas: tape formulationsand shell construction.New tape formulations such as Ferric Cobalt-an equivalent

to Cr02-and most recently, pure metal particle tapes, havemeasureably improved the high-frequency headroom, andextended overall response and signal-to-noise ratios to meet orexceed broadcast specifications.

Improvements in quality shell construction have helpedreduce wow and flutter and maintain near-perfect alignmentbetween the A and B sides of the cassette, while smoothing outtape travel within transport mechanisms in general. In short,cassettes have come a long way. They work better, theycertainly sound better, and have proven to be a reliablemedium."With this in mind, it was Eurnig's intention to design and

build a microprocessor-controlled tape transport mechanism

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Tom Bensen is technical representative for Eumig USA,Inc., Great Neck, NY.

which would fully exploit the cassette in terms of its technicalsuperiority, while providing the broadcaster with an entirelynew concept of automated program operation. As the design ofEumig's FL-IOOOcassette progressed, three basic goals wereestablished:a) provide a means to reach any position on tape, quickly

and precisely.b) engineer a versatile and convenient remote control

system.e) create a data bus system which would enable an external

intelligent device (computer) to communicate simultaneously and bi-directionally with several sub-systems.

To summarize, the FL-1000 design allows it to be addressedvia computer, be given a command, execute that command,and, move to the next event.In fact, up to sixteen FL-1000s may be connected at once,

suggesting obvious applications to the broadcaster. In anautomated application, several decks (perhaps four to six), canbe devoted to music playback. Two or three decks mayeffectively air and maintain the spot clusters, and timeannouncements can be accomplished by another deck. Onewould program all announcer breaks, another would be usedfor all P.S.A.s, while two decks would be used in the productionarea. One deck might be used strictly for automated networkjoining, for delayed newscasts, sport feeds, etc. In addition, onedeck might be devoted to the local newsroom. All decks can berandom accessed, playing any selection in any order.At the control center is a relatively inexpensive computer,

with at least 32K of memory. For sequence storage andprogramming, a floppy diskette drive may be used, and finally,a printer will notate automated Jogging of the broadcastmaterial.In the broadcast environment, such a system will provide full

random access to any point on tape. Cue tones are notnecessary, as the FL-1000 uses an optically-sensed counterwhich is universal among all FL-1000 decks. Due to thetransport design, which will be discussed later, this countersystem isaccurate to the digit, regardless of the number of plays.It is therefore possible to play selection 2, advance to selection 7,rewind and play selection 3, etc. This is accomplished via aseveral-step process, which begins by using the FL-1000 as adigital recorder.By means of three command codes (data onto tape, data

from tape and data onto tape and monitor); digital tape maybe recorded onto the tape via the bus lines and re-read.



All transmissions fed through the bus using a ten-pinplug/ cable arrangement, which contains the following:

Line Designation PinCode Line 8 RFT Ready for transmissionHandshake Line 7 BY Busy lineHandshake Line 6 H1Handshake Line 5 H2Data Line I Do negative logicData Line 2 D1 negative logicData Line 3 D2 negative logicData Line 4 D3 negative logicGround 9 *see notePower Supply 10 +5 volts (TTL)

*To avoid transmission disturbances byinactive machines.

For the purpose of a broadcast demonstration made byEumig at the last NAB convention, material was assembled inthe following manner:

During recording of broadcast material, counter locationswere noted and typed onto the computer CRT via the terminalkeyboard, thus creating an Index or Table of Contents for thatparticular cassette. When fully assembled, the FL-!000 is toldto write it (digitally) onto tape, by entering the command code,1001.The FL-!000 recognizes and confirms the command,

switches into recording mode, mutes Audio in and out, andsignals the receipt of data by illuminating the Source, Tape andRecord LEDs. Data line D2 becomes a serial data input (TTLsignal). At this point, the CPU can transmit data onto thecassette via this (D2) line. During data recording, BY, H 1 and H:iremain in force, thereby blocking access by other participantson the bus. The data recording is terminated when the CPUfrees the bus line. The FL- I000, in turn, frees the bus and stops.

The functions "data from tape" and "data onto tape & monitor"are treated identically; the data read from the tape aretransmitted via Do. The functions "data onto tape &monitoring" serves to recognize the end of the leader at thebeginning or end of the cassette. The user can select the coding.A self-clocking code with approximately 2,400 Baud isrecommended. The "data from tape" function may also be usedto search intervals between pieces of music. During theseintervals, the FL-1000 can also be used to load programs intothe computer.

The information brought through the bus-in this case theIndex-is recorded onto tape. When requested, the digital datais transferred back into the memory of the computer. All thatneed be done as a function of the program is to request amachine number and a selection number; for example, machine1, cut 2. The FL-1000 will then advance towards or rewind tothat location and execute the command. This is possiblethrough the rather unique transport mechanism. Fabricatedfrom die-cast magnesium alloy, it is a totally unconventionaldesign which uses no belts, pulleys, flywheels or solenoids. It is asingle-capstan, two-motor drive system, which uses a lightweight (under 7 grams) opto-electronic capstan and diskarrangement to both reference its speed ( 15,000 times persecond) and maintain reduced wow and flutter-quoted at0.035 percent WRMS or less. There is virtually no mass toovercome in attaining proper operating speed of 1Ys ips, whichwill occur from dead stop within 40 milliseconds.

As indicated, the FL-1000 can seek a counter position inresponse to a manual command from the user, or via thecomputer interface. The counter system, which operates fromthe take-up spindle, is also driven by a separate optical referencewithin the transport, when given a selection number by thecomputer from the index in memory. For that cassette, the FL-1000 "knows" to go to the appropriate counter position.

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The most probable concern, and most often asked questionis, what if the counter location changes due to tape stretching oraberration in tape packing density? There would be validconcern if addressed to a conventional dual-capstan or singlecapstan design which utilize flywheels. However, the FL-IOOOtransport does not change packing density through normalplay, fast-forward, or rewinding of the cassette, due to thereduced inertia placed on the cassette mechanism. Therefore,not only do the tape counter positions remain accurate, they areuniversal among all other FL-I OOO's.For example, if a selectionbegins at location 2248 in machine 3, and that tape is removed,placed in another FL-IOOO,rewound to the beginning, and toldto go to 2248, it will still be in virtually the identical location(±0.30 seconds). This tolerance is certainly more acceptablethan the lead time needed to "punch-up" a cartridge or thatwhich is necessary for an open-reel to attain proper speed andhave the tension arms settle in place.

At this time, there are quite a number of stations in the finalstages of incorporating the FL-1000 into on-air operation. Atthe vanguard is Associated Communications Corporation, anI I-station chain, based in both Pittsburgh, Pa and Tampa, FLAccording to director of engineering, Will D'Angelo, "Our goalwas to incorporate the FL-1000 in a series of steps within oursystem. The first step was to incorporate it into the system as adirect replacement for the cartridge machine. Secondly, wewere able to effectively interface it into a Cetec Schafer (System7000 Automation System) as a music playback system. Thethird step was to use a computer for simple sequencing andoperation. Finally, we are nearing completion of a full randomaccess system, using the FL-1000 for all phases of operation,including interfacing it into our station business system."

D'Angelo explains that they have been able to accomplish thebusiness system interface by using a frequency-shift keying(FSK) track on the right channel and commercial material

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recorded on the left channel in monaural for decks devoted tospots. Therefore, commercial Jogging is accomplished throughreading the FSK track and in turn, is interfaced with the stationbusiness system to generate direct billing.In addition to Associated Communications, there are other

broadcast facilities throughout the U.S. in the process ofincorporating the FL-1000. Some will be as elaborate asAssociated's full random access system, while other plannedapplications are for simpler, live-assist environments.

Subsequently, there are other applications for the FL-IOOOoutside the realms of broadcasting, with new ideas beingsuggested daily. Some possible examples are:

-Organization and rapid access to large archives of soundeffects and sound recordings, etc.

-Medical applications for the storage and quick retrievalof data and procedures in the operating theater duringsurgery.

-Automated time-indexed public address systems inindustry, hospitals, and institutions.

-Text storage in libraries with quick access to selectedpassages, recordings, and other stored information.

-Multi-media presentations, multi-vision, etc., withsimultaneous control of light and sound effects.

-Automated audio editing using several slave decks assources and assembling excerpts from each to create amaster (a similar concept to Umatic video editing inENG operations).

-Educational and instructional audio-visual training.

There are undoubtedly a multitude of other applicationswhich are yet to be suggested. It appears too, that the versatility of applications and functions of the FL-IOOO, wheninterfaced with a computer, are solely a factor of the limitationsof the softwave involved. •



JOHN NADY

Wireless MicrophonesOn Stage andin the StudioOn stage and in the studio, the performance of wirelessmicrophone systems may noi-vequal or sometimes surpassconventional methods.

W IRELESS TRANSMISSION OF SOUND was firstachieved around the turn of the century. However,only within the last several years has the evolvingstate-of-the-art finally yielded radio-transmitted

audio with both the fidelity and dynamic range required forapplications subject to the most critical ear. This achievementhad long been an evasive,yet natural, goal for radio transmission.

Interestingly (and fortunately), the impetus for thedevelopment of this high-level audio performance also dictatedthe need for simultaneous development of a highlyminiaturized radio transmission system. As it turns out, thescreaming rock-and-roll lead guitar places more demandingdynamic range requirements on a transmission system than anyother audio application. As a result, one of the most significantbreakthroughs in radio-transmission audio performance wasspawned in the course of developing a miniaturized wirelessmicrophone-type system for playing electric guitars withoutcords.

John Nady is founder and president of Nady Systems,Inc., an Oakland, California, based company whichmanufactures the Nasty Cordless FM tunable and theNady VHF wireless systems.

Although wireless microphones have been commerciallyavailable for over 20 years, hard-bitten longtime users cantestify that-until recently-performance was never evenclosely comparable to that of hardwired cords (especially foruse in demanding applications such as cordless electric guitars).The live entertainment and recording sectors of the general

audio market can most immediately reap the significantbenefits afforded by the imaginative application of this newlyavailable technology. Of the two, the live entertainment fieldhas a sizeable head start in advantageously utilizing wireless.This is because of its past willingness to compromise its audioperformance, as evidenced by the relatively widespread use ofearlier-generation wireless microphones. It is inevitable,however, that the recording industry will become more aware ofthe new possibilities now available in wireless systems whichmake no discernible sacrifice of audio quality. Already thevanguard innovators are beginning to pave the way inexploiting some of the advantages of going cordless in the

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studio. Since these advances and possibilities are still new tomost interested parties, 1will present in this article an overviewof the entire present wireless phenomenon as it applies to boththe entertainment and the recording industries. I hope thisoverall picture will create a better understanding of the excitingpromise that wireless microphone systems offer for stage andstudio.

USING WIRELESS SYSTEMS ON STAGEThe advantages of going cordless in live performances

basically fall into two categories: practical/ aesthetic, andtechnical. Under the former, there are: enhanced on-stagemobility, greatly increased theatrical possibilities, astreamlined, uncluttered stage appearance, and the performer'sability to hear the total sound offstage-du ring both soundchecks and performance. Of course, the most practical benefitof cordless operation of electric instruments and microphones isthe total elimination of potential electric shock hazards. Suchcommon shocks, caused by improperly grounded amplifiersand/ or other equipment malfunctions, have even proved fatalat times (Les Harvey of Stone the Crows and Keith Relf of theYardbirds were both electrocuted in this manner.)

A well-designed wireless system also offers several technicaladvantages over a hardwired cord. Cables are not idealtransmission systems for audio signals. Due to their inherentcapacitance, they act as lowpass filters and can severelyattenuate the highs when used with high-impedance musicalinstrument pickups. Although cables vary somewhat in thischaracteristic, most will start to "muddy" the sound at lengthsover 20 feet. In addition, cables act like antennae and pick upspurious noises from light dimmers, radio signals, power linesand other external sources. Used with certain combinations ofeffects pedals or amps, cords often pick up nearby radio stations

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and Clí'ers. All these things considered, it is no surprise that thelist of the hundreds of now cordless top acts reads like a "who'swho" that encompasses a broad spectrum of popular music,including such diverse styles as that of the Rolling Stones andHerbie Hancock. However, the natural education andemulation process has, especially in the last year or so, filteredthrough to the mass market, and a healthy rapid growth ispresently evident in this sector of the wireless field. The use ofthese new wireless systems is not limited to microphones andelectric guitars. Musicians of all kinds are discovering the joysof going cordless. Increasingly seen and heard on stageseverywhere are cordless electric saxes, trumpets, flutes (withpickups or tiny microphones), electric violins, mandolins,acoustic guitars (with pickups) and even an occasional exoticapplication such as miniature drum synthesizers. It is clear thatpossibly within several years-within a decade for sure, as theunderstanding of this technology continues to spread-cordlessoperation of most on-stage musical instruments will become thenorm.

USING WIRELESS SYSTEMS IN STUDIO RECORDINGWireless systems are increasingly finding their way into the

recording studio, and this is not surprising, considering thediverse ways in which cordless operation can aid today'srecording engineer. In fact, in the last two years, there haveprobably been a dozen popular recordings released (gold orbetter) which have utilized some form of wireless operationduring their production.

Before citing studio uses of wireless, I would like to brieflydiscuss our own experiences in this area. Most of theseapplications are ones I have used over the last five years or so inmy 8-track basement studio. Since we had been devloping a newgeneration of wireless systems during this period, I hadprototype new-generation wireless systems available for severalyears before we introduced them on the market in 1977. In fact,we have done completely cordless 24- to 32-track recordings(via extensive ping-ponging) utilizing all the wireless techniquesoutlined below.

Of course, our recording work was necessarily limited in timeand scope compared to larger commercial studios. Recently, wehave started work on an in-house 24-track recording andvideotaping studio, which will be equipped so that we canexpand our experiments in recording entirely wireless. Inaddition, although we haven't done an extensive survey of thepresent state-of-the-art, we have received quite a bit of feedbackabout studio wireless use in the last two years from customers,interested studio people, and the like, which will aid in theseexperiments. My own personal feeling is that there are stilladvantageous applications of wireless that haven't beendiscovered-and we hope to find and utilize them.

Originally, we were committed to exploring the concept ofthe totally cordless studio because of our interest in wirelesssystems. Not every studio owner will see the need toimmediately commit to cordless studio operation to the extentwe have. However, from what we have already learned, wirelessuse in the studio, as on the stage, should not be thought ofsimply as a "gimmick" to attract customers (although it hasobvious potential in this regard). Rather, studios interested inupgrading their overall operations (a necessity in thisincreasingly competitive field) should seriously study the waysof integrating this potentially valuable tool for what promises tobe its maximum benefit-a powerful aid toward improvingoperational efficiency.

The immediately obvious studio application of a wirelesssystem is to allow the electric musician the freedom of physicalseparation from his amplifier. In the studio, this introduces awhole new dimension of possibilities. For example, physicalseparation from a loud amp allows a musician to hear hisheadset mix at lower, more manageable, less fatiguing SP Ls-adefinite advantage on long sessions. The musician can even playfrom the control room, which can often give him a better "feel"than loud headsets in the studio. Also, the logistics of over-



Rod Stewart in concert using a Nasty Cordlessmicrophone.

dubbing on many takes can often be made easier with theengineer and musician sitting side-by-side in the control room.

In my own experience, I have even done dubs from out-ofdoors in my back yard (on exceptionally nice days)-whilebeaming the signal to my amp and communicating with myengineer via two-way wireless systems. Exploring suchpossibilities can be a refreshing change from the everyday rut ofstudio procedure and the wireless system makes it very easy.This can be important these days, as more and more studiosdiscover that artists are considering ambience and mood of theplaces where they choose to record.

There are several technical advantages of using a welldesigned wireless system in the studio. As discussed earlier,there is the freedom from high frequency cable loss, and fromspurious audio degradation. Another happy advantage of usinga wireless system in a studio, especially for electric guitars, is anup to 20 dB improvement in immunity against 60 Hz humpickup. In other words, a well-designed wireless system isactually quieter than a cord! Furthermore, wireless receivershave two outputs-with separate line and mic-level signalsthus eliminating the need for direct-box interfacing by allowingboth amp and direct feeds simultaneously.

Of course, the ultimate advantage of cordless studiooperation is probably "streamlining." The recording studio iseven more a maze of jumbled cords than the concert stage, and asignificant percentage of valuable studio time is lost in dealingwith this labyrinth during all phases of a typical session. As inour previous 8-track studio, all inputs in our new 24-track studiowill be on separate radio frequency channels. This greatlyfacilitates setup and breakdown. During a typical setup, wesimply choose the mic, attach it to the appropriate transmitterand place it in the desired location. This procedure is an

especially welcome labor shortcut on complicated multichannel takes. And, it's a pleasant change to walk aroundduring a recording session without having to watch out for thetangle of cords underfoot!

It is also advantageous to eliminate still more cords in thestudio by using a wireless headset monitoring system. We useour tunable FM transmitters in conjunction with high-qualityFM headphones. These work well for most applicationswithout any significant sacrifice of audio quality.

Sometimes, special recording needs arise where the use ofwireless monitoring is practically mandated; for example, bypercussionists when there is to be a lot of quick movement byseveral musicians between percussion instruments. Themovement is usually made extremely difficult by the entanglingof headset cords. For a specialized application, such as a moviesound track, separate input circuitry on the transmitterprovides for proper click-track cueing.

There is another advantageous studio use of the professional,well-designed FM tunable transmitter. It can be used inconjunction with several miniature FM portable radiossimultaneously as an aid to gauging the sound on typical lowpriced consumer equipment. This function is presently fulfilledrather inaccurately by the use of small "car speaker" typemonitors, generally driven by atypically overpowered, overlyclean amplifiers.

USING WIRELESS SYSTEMS IN LIVE RECORDINGLive recording can also benefit from the judicious use of

wireless systems. In such situations, the extra cable runs neededcan be a logistics nightmare. Not only are there moremicrophones on stage adding to the tangle, but long, difficultcable runs to the recording track are often needed. Sometimes,special staging needs entirely preclude the use of cords. Weworked on one project that is a perfect example of this-the

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acoustic side of Neil Young's recent sound-track album from hismovie, "Rust Never Sleeps." The simultaneous use of fourwireless channels (two on voice and two on acoustic guitar)allowed Mr. Young to wander about the stage unencumberedby cords. The enthusiasm of the engineers working on thisproject surely means many more such productions will beforthcoming. Such a quality recording would not have beenpossible just a few years ago with the previous generation ofwireless microphones.

Another logistics aid of wireless during live recording is in usewith remote microphones over the audience for applausepickup. Often, hardwiring a single such microphone over highbeams, etc., can take hours. From our experience, a lessexpensive wireless mic with less dynamic range than the topavailable equipment works quite well for this application.

VIDEO OR FILM SOUND RECORDINGVideo or film sound recording is the area of live recording

where the new generation of wireless microphones will maketheir greatest impact. Although wireless mies have been used foryears in this classic application, their generally poor sound,spurious RF noises, and unreliability made them a mixed blessing at best. The old-style wireless systems had limited signal-tonoise ratio, which necessitated the use of compressor/ limiters.Movie sound men suffered with all these audio degradations foryears. In recent years, more and more attention has been placedon high-quality, clean, noise-free sound tracks (witness, for example, the increasing use of Dolby noise reduction). It isespecially fortunate that the best of the new breed of wirelessmicrophones can guarantee studio-quality sound with noisefree, wide-dynamic-range transmission, even in the mostdifficult shooting locations-and with no annoying compression/ limiting.

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GUIDELINES FOR JUDGINGWIRELESS PERFORMANCE

A question remains-Does the wireless microphone imposeany compromises? Certainly, the specs of today's state-of-theart wireless systems meet the objective criteria of presentrecording requirements. However-as with all electronic signalprocessing equipment-subtle colorations are introduced thatsome may swear by, and others, at. Ideally, each interested userwill experiment and answer this important question for himself.

As discussed earlier, not all wireless systems performsimilarly. In fact, there is now a wide diversity in performanceon the wireless market. How then does the potential user choosea system in the confusing and mysterious arena of cordless radiotransmitters? By what guidelines does one judge a wirelesssystem?

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In order to understand the criteria by which tó make anintelligent choice, be aware of the potential problems exhibitedby wireless systems. These include: radio signal dropout (nullspots); interference; transmission range limitations; audiodegradations, including limited signal-to-noise (dynamicrange); and poor reliability. A well-designed wireless system isone that has maximized performance specs with respect to eachof these potential pitfalls. Let's discuss these problems.

DROPOUTS (NULL SPOTS/DEAD ZONES)While passing through the air from transmitter to receiver,

radio waves generally encounter a maze of reflective andabsorptive obstructions. When radio waves bounce off nearbysurfaces and meet in space such that one wave's crest encountersa reflected wave's trough, a 180-degree cancellation occurs. Areceiver antenna located at that point in space will register noreceived signal and a radio dropout will result. Although thesenull spots can occur at any receiver distance from thetransmitter, they are fortunately very infrequent up to Vi to 2¡3of the system's ultimate range at any given location.Nevertheless, in most critical applications, a maximum nullspot-free range is required. There are two methods of solvingthis problem currently offered by wireless manufacturersantenna diversity and receiver diversity. These two methods arein no way comparable in effectiveness.

Antenna diversity is actually a misnomer-it is no more thanantenna combination. In theory and practice, antenna diversityhas proven to be ineffective in significantly eradicating nullspots and improving range.The only reason for the existence of antenna diversity units

on the market is that they are a lot simpler and cheaper toproduce than receiver diversity systems.In receiver diversity, two separate receivers and two separate

antennae are employed to process the single transmitted radiosignal. In a well-designed true-diversity system, a totally silentcomparator circuit continuously monitors the received RFsignal strength of both receivers and instantaneously selects theaudio output of the receiver with the stronger signal. In thisway, there can be no vector cancellation of the received signalsas in antenna diversity, since the two antennae are completelyseparate.The US Navy researched the problems of null-spot dropout

in its critical radio applications for years and concluded thatpost-detection diversity receiver switching was the only possibleway to mathematically eliminate dead zones. Although receiverdiversity systems are more costly than a single receiver withseveral antennae, the dramatic improvement in receptionreliability is well worth it.

INTERFERENCEUnfortunately, there are not yet any radio frequencies set

aside by the Federal Communications Commission in theUnited States (or by similar radio governing boards elsewhere)solely for wireless systems. Consequently, a potential usershould be aware of the frequency allocations in the locales inwhich he plans to use his system(s) to avert any potentialinterference problems.There are two frequency bands most successfully utilized by

today's professional wireless systems: the commercial FM band(88-108 MHz), and the VHF business and TV channels band(150-216 MHz). The wireless systems operating in thecommercial FM band are tunable so that they can be tuned toblank spots between FM stations. The VHF systems are allfixed-frequency, and cannot be tuned to open frequencies. Forapplications such as traveling musicians, live recordings, etc.,where clear channel accessibility and freedom from randominterference is a must in all locales, a well-designed, frequencystable tunable system, is recommended. Even for fixed locationuse, such systems offer a maximum of immunity from anypossibility of interference from CB'ers, cabs and the like sincesuch business bands are so far removed from the commercialFM band.



The Rolling Stones in concert. Note 'ne '.i.asty Cordlesson Richards' back.

Designing a usable VHF system is complicated by the factthat, since it is not tunable to an open channel, it has to be asimmune as possible from weaker signals on the same frequencyand from strong adjacent business or TY channel interference(i.e., a good capture ratio of I dB or less and at least 100 dBimage and spurious rejection). Therefore, to compete with atunable system's usability in all locales, the VHF system must beextremely well designed. With careful selection of frequencies,YHF systems do offer the advantage of enabling the maximumnumber of channels to be operated in one location. For thisreason, in the 24-track studio weare currently building, weplanon using more VHF systems than FM tunables. When finished,this studio will probably have more radio mies operating in onelocation than any previous setup ever attempted! Theimportance of proper design to prevent any radio crosstalkbetween adjacent operating units is especially critical in anysuch multi-channel application.

TRANSMISSION RANGEA well-designed wireless system generally has a usable range

of about 150feet minimum under adverse conditions, and up ro1,500 feet line-of-sight. Receiver diversity (two receivers withseparate antennae) provides greater usable range than singlereceiver or antenna diversity operation, all other conditionsbeing equal. Different applications, of course, require differentoperational ranges. For on-stage use, a wireless system mustprovide a totally solid radio link between performer and ampfor at least I00 feet. Due to sound travel, there is an acousticdelay of about 1-00 milliseconds at that distance. It isdifficult, ifnot impossible, for musicians to keep in time at longer distancesand longer acoustic delays. For studio use, these delays aregenerally not a problem.

For all the applications we've discussed, wireless systemswhich provide at least 150 feet under the most adverseconditions will serve quite well. Not all units presently available

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DYNAMIC RANGEThe greatest single breakthrough in the performance of

wireless systems is the recent dramatic improvement in dynamicrange offered by the best of the new-generation units. Signal-tonoise has improved from a previous high of about 65 dB, to over100dB. Bycomparison, a commercial FM station only registersabout 70 dB signal-to-noise through a high-quality receiver,and NASA's ultra-sophisticated deep-space network onlyabout 90 dB signal-to-noise.

1t was discovered early in the development of wireless systemsfor playing cordless electric guitar that about 100dB signal-tonoise was needed for immunity from annoying background hisswhen played at full volume. Earlier systems (all of which are stillon the market) relied on compressor limiters on the transmitterinput to handle the wider dynamic range excursions regularlyencountered in typical usage. This results in the unnatural"squeezed" sound on the louder signals so typical of limiteroperation and makes such systems barely adequate for mostapplications. The best new extended-dynamic-range systemshave no need for compressor limiters, and are thus comparableto hard-wiring in accurately handling any of the loudest audioinputs .Given the highly competitive atmosphere in today's wireless

arena, much secrecy still necessarily surrounds the exact detailsof the technology which effected this vastly increased signal-tonoise. It is well-known, however, that the key process used iscompanding. Of course, companding has helped to quiet audio

can reliably deliver this level of range performance. Publishedspecs can often be misleading in this respect and it is highlyrecommended that one test a system for the range necessary inany expected application.

AUDIO LIMITATIONSThe greatest variation in performance features between

wireless systems available today is found in transmitted audioquality. As a result, the wireless consumer can choose betweenavailable products (often priced the same) whose audioperformance varies as much as night and day.

A word of caution: since most wireless systems are a relativelyexpensive investment, one should do careful market researchbefore choosing. Listen carefully to the several top choicesavailable. Even among those companies now offering new,improved systems, there is still significant performancevariation evident. Some manufacturers are obviously furtheralong than others in developing and implementing the newtechnologies.

Distortion, frequency response, and dynamic range are thethree key parameters in measuring the audio quality of anyelectronic processing equipment. Let's consider each of thesecriteria with respect to the operation of today's wireless systems.

DISTORTIONMeasuring distortion in any piece of electronic gear can be a

numbers game and wireless systems are no exception.Published specs often quote a figure that represents a best-casesituation that may not reflect realistic in-field usage. Undertypical conditions, most wireless systems will yield anapproximate THO of 0.7-to-3 percent, depending on thetransmitted audio level and the audio frequency. The best newgeneration systems improve that performance to about 0.2-to-0.6 percent THO. Discerning the desirability of the subtlecolorations introduced into the transmitted audio at these lowerdistortion levels becomes a subjective decision and depends onthe application intended.

FREQUENCY RESPONSEFrequency response in today's professional wireless systems

range from 100-7,000 Hz (±3 dB) to 20-20,000 Hz (±3 dB).Again, the intended usage can dictate the frequency responseneeded. Published specs tend generally to be overly optimistic,so for critical applications, a careful listen or on-bench testing isrecommended.



processing systems in the past, but its successful application towireless systems awaited the overcoming of many formidableobstacles, including unacceptable audio degradation and therestraints of miniaturization ..

Schematically, the process is similar to the familiar use ofnoise-reduction companders in recording, where encoding anddecoding enables audio reproduction through a noisy medium(recording tape) without retention of that medium's inherentnoise. In this case, encoding (compression) at the transmitterinput is matched by complimentary decoding (expansion) at thereceiver output. The noise of the radio transmission process,which previously limited the final output signal-to-noise, isentirely circumvented. Since lower level radio "buzzes" and"whooses" typical of weakly-received RF signals are alsoeliminated in this manner, both effective usable range andincreased immunity from null spots is also significantlyimproved.

Of course, anyone familiar with the different compandingschemes in the recording process will be aware that audioproblems can be introduced by the use of improperly designedcompanders. And so it is with the present state-of-the-art inwireless systems. Significant performance variation is evidentamong products offered by the several competing manufacturers that have so far introduced wireless systems featuringextended dynamic range using companding. For example, thesignal-to-noise ratio in these differing units varies from about80 dB to slightly over 100 dB.. Also, each design exhibits varyingsuccess in dealing with the audio degradations most common tothe compander: "breathing" (annoying auditory changes in thebackground hiss level), "pumping" (inaccurate input-outputsignal tracking), and transient response, especially to low-levelsignals. Since some companies have been working at thedevelopment of this technology a Jot longer than others, thissituation is not surprising,

Again, especially for the most critical intended applications,a comparative listen to the different systems available underworst-case conditions will prove invaluable in making anintelligent choice.

RELIABILITYLike any piece of very complicated electronic gear, wireless

systems are subject to breakdown from parts failures, roughhandling, or just poor production and design. Eachmanufacturer has his own approach to solving this potentialproblem. The ultimate test of reliability is proven ruggednessand roadworthiness. Because the market is still so relativelyundeveloped for many of the applications discussed above, thepotential customer presently has only one way to gauge thisvery important factor in deciding which system to buy. Onlypeople who have been using the various wireless systems for areasonable length of time can testify to a brand's typicalreliability. The primary users of the new generation of wirelesssystems so far have been the top touring pros. The potentialconsumer would do well to find out what wireless systems theseartists are consistently using-he can generally be sure that theirprofessional sound crews have researched the market carefully.

* * *As a longtime advocate of the use of wireless systems, it is

especially gratifying for me to witness the ever-broadeninginterest in this technology. With the dramatic improvements inperformance now available, I feel the widespread acceptance ofwireless systems isjust around the corner. The timing is now justa matter of education. A continuing healthy growth in thegeneral awareness of the diverse possibilities of the newwirelesstechnology will hasten the day when wireless systems will taketheir rightful place as a valuable tool in all phases of theentertainment and audio industries. •

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LESLIE B. TYLER

Broadcast SignalProcessing: Thedbx Approach

Presenting a brief overview of methods to keep it louder,quieter, cleaner, compressed-expanded Why, theresnothing to it!

BROADCASTERS TODAY face a persistent problem; tomaintain a consistently high level of audio qualitywhen switching from live announce mikes, to records,to remote coverage. The "sound" of the live mike in

the studio is excellent, but the phonograph records are marredby scratches and surface noise; the cartridge's high end isstrangled in dropouts and high frequency saturation. Remotefeeds are replete with hum, hash, and other garbage picked upover land lines.One simple solution is to reduce the quality of all the pro

gramming to the lowest common denominator; simply run thestudio audio channel across town on a telephone line, then addtape delay using a modified cartridge machine! But thisprocedure is hardly in keeping with the goal of producing highquality audio for the station's audience. Besides, productswhich can better solve the broadcaster's dilemma of how toprovide a consistently high level of programming whenswitching among various sources are now available. Of course,some of the most successful applications incorporate noisereduction.

NOISE REDUCTION THEORY REVIEWEDThe compander (compressor/ expander) has been around for

some years. Many attempts have been made to apply thisconcept to professional audio and broadcasting, but most ofthese have been less than successful for technical reasons.The dbx approach uses a voltage-controlled amplifier as the

control element and a true RMS circuit to sense the signal.These optimize the compander performance for ease ofoperation, maximum noise reduction, and increased headroomfor the storage or transmission medium.The noise reduction system consists of an encoder (with a

constant 2:1 compression ratio) and a complementary decoderto precisely recreate the dynamic range of the original programmaterial. The noisy medium (tape recorder, telephone line,microwave link, etc.) is sandwiched between the compressorand expander, with the dynamic range of the input signal cut inhalf during passage through the noisy channel.Noise reduction is due, in part, to the masking effect of the

program signal on the channel's noise level. For example, highlevel musical signals may be loud enough to mask theperception of most noisy channels even without noise

Leslie B. Tyler is Chief Engineer of dbx, Inc.,Newton, Mass.

reduction .. During quieter passages, however, the floor noisebecomes audible. By placing the compressor before the noisychannel, the signal going through the channel is kept at highlevels, so that more effective masking can take place. Onplayback, the expander restores the signal level to its propervalue, while pushing down the noise at the same time. Duringperiods of silence in the input, channel noise is pushed down sofar as to become inaudible.For a given signal-to-noise ratio, levels within the channels

can be held down. The lower signal levels almost invariablyresult in less distortion of the signal. Because of the noisereduction system's action, the normal degradation of the signalto-noise ratio with less signal will not take place. In addition, anincrease in headroom is also realized.

THE dbx APPROACH TO COMPANDERSFor noise reduction to work in reality, a more sophisticated

approach than has been suggested above is necessary. For acornpander to operate properly, the compressor and expandermust operate as mirror-images. To control the expansion/compression operation, each must have a signal detector.There are three common types of signal detection: peak,

average, and RMS. Since peak and average detectors aresensitive to phase shift, these types of signal detectors areinadequate for broadcast applications. To cope with timedispersive media-channels with non-flat group delay, whererelative phase shifts of different frequencies can cause severealterations of wave shapes-dbx uses RMS level detectors inboth compressor and expander. RMS detection measures thesum of the energies present in the signal and is not sensitive tophase shift introduced by time-dispersive media. RMS level isunaffected by irregular group delay. Peak and average level,however, are significantly altered. The use of RMS detectorsinsures much closer tracking between compressor and expanderlevels than would be possible with other detection schemes.Since the dynamic range of live music sometimes approaches

120 dB, a means of automatically varying level in response tothe detector's output over a 60 dB range must be used to achievethe 2: I compression ratio. In addition, the dynamic range of thegain control element itself must be 120dB or more, in order toavoid degradation of the input signal. To fulfill these criteria,dbx employs a voltage-controlled amplifier (VCA), which useslog-anti-log techniques. At the same time, the VCA controlconstant of -6 mV/dB, with OV control corresponding to O dB(unity) gain, is a fortunate match for the RMS detector's outputconstant of -6 mV/dB, with O V output corresponding to apresettable reference level.



To better cope with high frequency noise content within thechannel, and to combat tape modulation noise, a highfrequency pre-emphasis of approximately 12 dB is used in theencoder, with a complimentary de-emphasis in the encoder. Thede-emphasis serves to reduce high frequency noise by 12 dBwhen the signal is decoded.

Unfortunately, the 12 dB pre-emphasis alone would impose aheadroom requirement on the transmission channel which maynot be met in reality. Tape recorders which run at slower speedsare especially prone to high level, high frequency, saturationeffects. To deal with this problem, dbx includes level detectorpre-emphasis. This causes the RMS detector to weigh highfrequencies more heavily than low frequencies in order tocomplement the signal pre-emphasis used and the anticipatedoverload situation.

TYPE I AND TYPE II NOISE REDUCTIONSince overload characteristics of tape machines vary

drastically with their operating speeds, different amounts oflevel detecting pre-emphasis may be required. For example, thedbx Type I system is optimized for operation with high-speedtape machines (15ips or greater), or transmission channels withwide bandwidths and generous high frequency headroom.Detector pre-emphasis begins at approximately 1.8 kHz, andboosts high frequencies by as much as 19 dB. The Type Idetector bandpass is 20 Hz to 27 kHz.The Type II system is appropriate when the bandwidth of the

medium is narrow (particularly at the high frequency end),when peaky high frequency response is present, or whenheadroom is limited at high frequencies. Type II is thereforeespecially useful for 31.íips and 71/iips tape machines, as well astelephone lines and other restricted media. Detector preemphasis in the Type II system begins at approximately 440 Hz,and reaches a maximum boost of20 dB. The bandpass is 30 Hz

to IO kHz. When used properly, both systems can deliver inexcess of 100 dB dynamic ranges.

BROADCAST NOISE REDUCTIONFor the broadcaster, the primary limitations to signal-to

noise ratio lie in STLs (studio-to-transmitter links), telephoneline feeds, cartridge tape machines, and video tape recorders.Although modern broadcast consoles have excellent signal-tonoise ratios, the best console in the world cannot show off itswide dynamic range when processed through a noisy STL.Telephone lines are notoriously noisy, and when adequate

bandwidth is available for proper encoder/ decoder tracking,can greatly benefit from a noise reduction system. Furthermore,cartridge machines frequently suffer from headroomlimitations and poor signal-to-noise ratios. Audio sections ofvideo tape recorders are often relegated to second place in theiroverall design. For these situations (noise reduction aroundchannels with limited high frequency headroom and response),dbx recommends Type II noise reduction.When noise reduction is added to all station sound sources,

the differences in dynamic range between these sources may beso small as to be inconsequential. A note of caution: when usingany noise reduction, equipment such as equalizers, compressors, etc., must be kept out of the encode/ decode loop.While the linear 2:1 compression/ expansion ratios insure thatlevel variations will not cause decode errors, any alteration offrequency response or dynamic range will introduce trackingerrors.

SATELLITE COMMUNICATIONSYSTEM APPLICATIONS

A compander system can be used to compress the audiosignal sent around the world via satellite link. Unlike the dbxcompanding systems described earlier, the system designed for

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satellite communication system applications is a 3: lcompressor/ expander system. It contains highly specializedpre-emphasis and de-emphasis networks and very tightfrequency response and tracking specifications. The dbx 321compander system was built on an OEM basis for NationalPublic Radio System's ground station installation. It allowsNPR to transmit high quality audio signals over otherwise verymarginal satellite channels.

CUSTOM-TAILORING COMPRESSION RATIOS FORDIFFERENT BROADCAST APPLICATIONSMany areas in broadcasting require varying compression

ratios suited to particular applications. As an obvious example,the classical music station might desire a gentle compressionratio for much of its programming as well as a higher ratio toimprove intelligibility during news broadcasts.

Unlike compressors in the noise reduction systems, thiscompressor is a feed-forward device, so that very highcompression ratios (limiting) can be achieved with absolutestability. The maximum compression ratio available is oo ; 1,wherein no increase in output takes place once the input isabove the compression threshold.The level detector used is an RMS detector. It has been

chosen here because of its unique time constants and thecloseness of its response to that of the human ear. The timeconstants of RMS detectors are such that more weight is givento a large increase in level than to a small increase in level. Thisresults in an attack time which varies with the amount of changein signal level, getting shorter for larger level changes. Theattack time may vary from l5ms for a IO dB change to a 3ms for30 dB change. The release rate (not time) is fixed at 120dB/sec{dbx model 160 specifications).The compressor /limiter provides a gentle, natural sounding

compression effect, keeping levels stable on an RMS basis,

similar to the way in which the ear perceives levels. Since it willnot over-react to peaks, the compressor/ limiter should not beused as a device to prevent instantaneous over-modulation of atransmitter. However, it can act to control levels in a naturalsounding fashion, before the signal is sent to a final, peakactivated, limiter.

EXPANDING DYNAMIC RANGEAlthough some form of compression is a broadcast fact of

life, some broadcasters, seeking to enhance radio station sound,are experimenting with dynamic range expanders. Stations areusing this equipment to reduce surface noise from records,emphasize detail in the nuances of the music, and generallycapture a greater sense of the live performance. They are alsofinding that use of such signal processors can contribute tostation "identity," which helps listeners recognize the station byits special sound character.Splitting the audio frequency range into several bands brings

freedom from undesireable side effects of expansion, since timeconstants are tailored to fit the bandpass of each section, andexpansion of low frequencies will not cause pumping of highfrequencies, and visa versa.

CONCLUSIONIn today's highly compet inve marketplace, increasing

numbers of broadcasters are seeking high quality signalprocessors to custom tailor their station's sound to provide amarketing edge, to provide maximum talk power, or to clean upa noisy land line.As with many companies, dbx engineers are cognizant of

broadcasters' needs, and are interested in establishing an ongoing dialogue on signal processing equipment and signalprocessing problems. •

ocoOl

Model 380 is theupgraded successor to ourwell-known 375, used inhundreds of studios andstations around the world.With your tape transportand our 380, you have theultimate analog recorder.Features of the 380include:

full compatibility withhighest-coercivity tapes.o Two "workhOrse" EOand bias settings, plusan optimized modewith separate setup forbest performance from"super" tapes.o compatibility withvirtually any combinationof transports and heads.o SYNC reproduce andexclusive auto-mute.o Remote control of allfunctions.

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oAdvanced circuitry toreduce the effects of tapecompression and phasedistortions.o Unprecedented signaland bias headroom for

The Model 370 is intended forroutine replacement use.

. It is compatible with most

Pere fect studio transports and awide variety of originaland replacement heads.

Pa• The 370 will make "new"machines out of yourIr. . older studio recorders.delivering superior performance and greatreliability. $580.00

use the 380 to create new,ultimate-performancerecording aqutpment, or togive your Did tape or magñlmrecorder a sound soclean you must hear it tobelieve it. $820.00

For more information,see your distributor orcontact us today.

lnovonics Inc.ol!)

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JOHN M. WORAM

What's Newat the FCC?

EARLY THIS YEAR, optimistic Washington watchersthought they may have detected signs of life on 'M'Street, Northwest. At the headquarters of the FederalCommunications Commission, it appeared as though

the broadcast and recording industries were about to get aninvigorating boost: In April, the Commission was expected tochoose from among five competing AM stereo systems. Atabout the same time, the Commission was also going to resolvethe matter of FM quadraphonic broadcasting.Finally, it appeared that 1980would be the year in which the

FCC broke a long-hallowed tradition, and actually began tohelp the industry it serves.

Guess again! Perhaps in recognition of its position as themost inefficient federal agency within the US Government(according to the General Accounting Office), the Commissionhas once again managed to stifle technological advancement.

Commission-watchers speculate that AM stereo is nowstalled until next year at least. FM quad is in no better shape,despite the fact that the matter has been before the Commissionsince August, 1971!

AM STEREOFive AM stereo systems have been competing for FCC

approval: Motorola, Magnavox, Harris, Belar, and Kahn. InApril of this year, the Commission approved the Magnavox

system, setting off industry-wide protests. (At least some of th.howls were predictable: with five systems in the running, anydecision at all is guaranteed to displease 80 percent of thecontestants.)In the ensuing debate, it was learned that the FCC had

prepared an "evaluation matrix," in which each system wasgraded on mono compatibility, interference characteristics,coverage, transmitter stereo performance and receiver stereoperformance.

At first, the Commission denied a request (by Harris) to makethe matrix public. Meanwhile, FCC staffers, preparing tojustify the pro-Magnavox decision, acknowledged "ambiguitiesand omissions" in the record.

In its August 4 issue, Broadcasting Magazine published a"revised AM stereo evaluation matrix," presumably derivedfrom FCC data. This shows Motorola as the high scorer, with67 points (out of a possible 100). Belar is second, with 53, andMagnavox and Kahn, with 51 each, are tied for third. In fact,only Harris comes in lower than Magnavox, scoring 50 points.The Commission has not yet issued a satisfactory explanationfor designating one of the third-place systems as the winner.However, it should be noted that the matrix does not give scoresfor coverage or receiver stereo performance to any system, dueto insufficient data. Obviously, filling in the missing data couldhave a significant effect on the ratings. Did the FCC base its Q.

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decision on the missing information? We don't know, but at theFCC, chief scientist Stephen Lukasik apologized for the"ambiguities, discrepancies and inconsistencies."

From the thoroughly muddled proceedings to date, one thingappears clear: the FCC is not in command of the situation. Itseems to be incapable of making an intelligent evaluation, evenif this might be (as Commissioner Quello inquires) that all fivesystems are minimally acceptable.

If we may indulge in a bit of over-simplification, it wouldseem that the Commission might make one of the followingstatements:

A. One system is clearly superior.B. One system is not clearly superior.C. We can't tell if A or B is correct.

On July 31, the Commission approved a Further Notice ofInquiry on AM stereo, which seems to indicate that C is theanswer. That being the case, why did they approve Magnavoxin April?

In engineering matters, one need not be embarrassed byrequiring more data in order to reach a conclusion. However,when conclusions are published before the facts, we must cometo some depressing conclusions of our own concerning thecompetency of our federally-appointed decision makers.

We suggest that the industry deserves better treatment fromits regulators. When setting standards that will have a long-termeffect on radio and recording, we don't expect the FCC to play"let's run it up on the flagpole, and see if anyone salutes." By astroke of good (or maybe bad) luck, when the Commission ranMagnavox up on the pole, no one saluted, and the flag wastaken down quickly, with apologies. That's really unfair to the

ocoO>,....

The TENTELOMETER®measures tape tension while yourtransport is in operation. so you can "see" how your transport ishandling your tape; high tension causing premature head and tapewear. low tension causing loss of high frequencies. or oscillationscausing wow and flutter. Send for the Tentel "Tape Tips Guide".The T2-H20-ML sells for $245 - complete.

If something SOUNDS FISHY itmev be vour fish scale approach tomeasuring tension.

The TenteI Tape TensionGage is designed to diagnose problems in yourmagnetic tape equipment.Virtually all recorder manufacturers use and recommend the TENTELOMETER®for use with their equipment.

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winner, to the losers, to all of us. In fact, the"winner" becomes aloser too, and the FCC's already tarnished image gets anotherscratch on it.

FM QUADAt first, it may seem unfair to blame the Commission for the

apparent "death" of quadraphonic sound. Indeed, someCommission insiders cite the poor showing of quad in themarketplace as justification for taking no further action.

However, it is a fact of life that the record marketplace isprofoundly influenced by broadcasting practice. It is also a factthat, over the past ten years, the Commission has allowed somequad systems on the air, while others were kept off. Therefore,the listening public has not been able to hear all the contendersin the quad marketplace. Based on what has been heard, thepublic has not come to the support of any quad broadcastsystem. And manufacturers, anticipating eventual action by theCommission, have become reluctant to invest in any of thecompeting systems, for fear that it may be rendered obsolete,once the Commission does make up its mind.

And so the matter stands. But at last, the Commission hasfinally acknowledged that even the discrete (4-4-4) systems arecapable of operation within the present broadcasting system.So it would seem that a standard might be written that wouldallow such broadcasts to take place. (It should be noted that theCommission has acknowledged that matrix standards areunnecessary, since such programming is already possible underexisting stereophonic standards.)

Well then, we can expect the Commission to finally dosomething! Right?Wrong! The Commission wants yet another period of

comments. After all these years, they now want to know if theyshould; A, specifiy a compatible discrete system, or B, leave thematter entirely up to the marketplace. The FCC calls the latter a"general standards" approach.

Well, "column B" certainly sounds like the good-oldAmerican way of doing business, doesn't it? It's a wonder itdidn't occur to them ten years ago, when there was still amarketplace out there.

But "specific" or "general," what's the realdifference betweenA and B? If a specific discrete system is standardized, thebroadcaster may either use it, or not use it-the choice is up toeach station, and its own unique marketplace. If a generalstandards approach is in effect, the broadcaster has exactly thesame options. The significant difference is that this "nostandard standard" offers no frame of reference to either thebroadcaster or the manufacturer. It needlessly muddies thewaters, since the Commission has already determined that adiscrete system based on the QSI /RCA proposals is preferable,and-unlike the AM stereo situation-there has been nosignificant opposition raised.

Of course, the Commission is no doubt sensitive to thetrouble it brought on itself with AM stereo; a "non-decision" onFM quad will spare the Commissioners more discomfort.However, the industry has suffered through ten years of pain,countless millions of dollars in research, and man-years beyondcounting have been wasted before the Commission. After allthat, surely we deserve the courtesy of an intelligent responsefrom the Commission. Just one, that is-it needn't become ahabit.

Its been said before. that the Federal CommunicationsCommission is a little out of touch with the broadcast industry.In fact, the National Association of Broadcasters (NAB) hasrequested that a committee be set up between government andindustry, to help facilitate a comprehensive approach to AMand FM matters now before the Commission. The FCC hasconsidered the request, but has decided to postpone action forthe time being. Enough said? •



~ClassifiedClosing date is the fifteenth of the second month preceding the date of issue.Send copies to: Classified Ad Dept.db THE SOUND ENGINEERING MAGAZINE1120 Old Country Road. Plainview, New York 11803

Minimum order accepted $10.00.Rates: 50¢ a word.Boxed Ads: $25.00 per column inch.db Box Number: $1.00 per issue.

Frequency Discounts: 3 times,10%; 6 times,20%; 12 times,33%.

ALL CLASSIFIED ADS MUST BE PREPAID.

BX20 AND BX10 AKG reverberation systems. FOR IMMEDIATE DELIVERY. UARProfessional Systems, 8535 Fairhaven,San Antonio, TX 78229. 512-690-8888.

THE LIBRARY ... Sound effects recordedin STEREO using Dolby throughout.Over 350 effects on ten discs. $100.00.Write The Library, P.O. Box 18145,Denver, Colo. 80218.

JFET TUBE REPLACEMENTS for firstplayback stages in most Ampex Professional audio tape recorders/reproducersavailable from VIF International, Box1555, Mountain View, CA 94042. (408)739-9740.

IVIE ELECTRONICS REAL-TIME ANALYZERS, etc. Very slightly used demonstrators at discount. Full factory warranty.Money-back guarantee. JML Company,39,000 Highway 128, Cloverdale, CA94525.

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·RECORDING STUDIO

CALF AUDIO157 Gray Road Ithaca NY 14850 <607>272·8964

FOR SALE

BEST PRICE-IMMEDIATE DELIVERY &FREE consultation on TEAC Tascam,Ampex, Sennheiser, Eventide, StudioMaster, UREI, BGW, EV, Lexicon, ADR,Orban, JBL, Beyer, AKG, Technics,MXR & more. Paul Kadair's Inc., BatonRouge, Louisiana, (504) 924-1001.

REELS AND BOXES 5" and 7" large andsmall hubs, heavy duty white boxes. W-MSales, 1118 Dula Circle, Duncanville,Texas 75116 (214) 296-2773.

USED RECORDING equipment for sale.Soon to be in Hollywood. Dan (415)232~7933.

STUDER 867 2/2 VU mint, little used DBX158 with 2 #410 modules-mint. Royal(404) 253-6419.

PROFESSIONAL AUDIO EQUIPMENTShop for pro audio from N.Y.'s leader,no matter where you live! Use the Harvey Pro Hot-Line. (800) 223-2642(except NY, AK, & HI) Expert advice,broadest selection such as: Otari,EXR, Ampex, Tascam and more. Writeor call for price or product info:Harvey Professional Products Division

2 W. 45th StreetNew York, NY 10036

(212) 921-5920

UREI: FOR IMMEDIATE DELIVERY mostitems. UAR Professional Systems, 8535Fairhaven, San Antonio, TX 78229. 512-690-8888.

AMPEX, OTARI & SCULL Y recorders instock for immediate delivery; new andrebuilt, RCI, 8550 2nd Ave., Silver Spring,MD 20910. Write for complete product list.

AMPEX AG-350-2: consoled, $1300.00;unmounted, $1100.00. Crown 800 transports-quad heads, $500.00; with electronics, $650.00. Magnecord 1028-2$225.00; no electronics $75.00. (215)338-1682.

ELECTRO-VOICE SENTRY Ill, SentryIV-8, and Sentry V studio monitor speakers.E-V raw speakers and pro-music products.Otari professional recorders. Best pricesimmediate shipment. East: (305) 462-1976, West: (213) 467-5725.

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WANTEDRECORDINGEQUIPMENT

OF ALL AGES ANDVARIETIES

microphones, outboard gear,consoles, tape decks, etc.

Dan Alexander6026 Bernhard

Richmond, Ca. 94805 USA(415) 232-7933 or (415) 232-7818

AMPEX AG440-4, PORTABLE CASES,two track heads included, excellentcondition. Asking $3200. SA Audio,6252 E. 20th, Tucson, Ariz. 85711. (602)747-7628.

dbx 155: FOR IMMEDIATE DELIVERY.UAR Professional Systems, 8535 Fairhaven, San Antonio, TX 78229.512-690-8888.

AMPEX 440B PROFESSIONAL eighttrack recorder/reproducer. Excellentcondition, never abused. $7,000. CallFred or Mike at (516) 489-6177.

AMPEX, OTARI, SCULLY-In stock, allmajor professional lines, top dollar tradeins: 15 minutes George WashingtonBridge. Professional Audio Video Corporation, 384 Grand Street, Paterson,New Jersey 07505. (201) 523-3333.

SCULLY, NEW and used: FOR IMMEDIATE DELIVERY. UAR Professional Systems, 8535 Fairhaven, San Antonio, TX78229.512-690-8888.

'/.-INCH TAPE duplicating system. SixCrown 800 transports. New 4-channelheads. Solid state. Mint. $4,200.00.(215)338-1682.

oco(j)

ORBAN. All products in stock. FOR IMMEDIATE DELIVERY.UAR ProfessionalSystems, 8535 Fairhaven, San Antonio,TX 78229.512-690-8888.

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TEST RECORD for equalizing stereosystems: Helps you sell equalizers andinstallation services: Pink noise in 1/3-octave bands, type OR-2011-1@ $38.00.Used with various B & K Sound LevelMeters. Bruel & Kjaer Instruments, Inc.,185 Forest Street, Marlborough, Mass.,01752.

CASHFORYOUR 16TRACKSTUDIO PACKAGE

Must be complete and in perfectworking order. No brokers. Princjpalsonly. Call Mike at (703) 734-!:1300(days) or (703) 451-7481. (eveningsor weekends).

LEXICON224Digital Reverberation.FORIMMEDIATE DELIVERY. UAR Professional Systems,8535 Fairhaven,San Antonio, TX 78229.512-690-8888.

PRO-SOUNDequipment. Mail order discount catalog free.Write or call Soli1ixCo.,Dept. D, P.O. Box 58, Indian Head, MD20640(301) 753-6432.

BGW: FOR IMMEDIATEDELIVERY.UARProfessional Systems, 8535 Fairhaven,San Antonio, TX 78229.512-690-8888.

FOR SALE: NEVE CONSOLE 24 tr.,3M M79 24 tr. tape recorder, includingbrand new16trk headassm.,24tr. Dolbys,3M M79 2 tr. w/Dolby, Crown & CM Labpwr amps., UREI Speakers, UREI 1/3octave eqs., Kepex Rack, AKG BX-20reverb, everything needed for 24 trkstudio $117,000 takes all. Call TimHunnicutt (602) 258-1610or 258-9282.

I - - - - - - - -- I

IIII

REBUILD YOUR MOTOR

CAPSTANMOTOR(AMPEX,SCULLY 7.5/15 IPS)Replaceshaft or stator $140Replaceshaft and stator $210

Replaceupper sleevew/ballbearingIncludes new shaft $160

Includes new shaft & stator $230TAKE-UP & SUPPLYMOTORReplaceshaft or stator $95

Replaceshaft and stator $140

• Electrosound & 3.75/7.5 IPSmotorsprice upon request

• All capstan shafts 440C stainless• Take-up & supply motors, mfrs

original specifications• 3/6 weeks AR0-(201) 429-8996-

Warranty• Shipments UPS COD unless creditestablished.

9WestinghousePl., Bloomfield,NJ 07003DICKINSON

Auth. Ampex Repair StationL _J

CAMUIANS!Interested in semi-promultitrack recording?Headquarters for. {f]fj!if[f}Q

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AKG, E/V, Sennheiser Shure, Neuman;FOR IMMEDIATE DELIVERYmost models. UAR Professional Systems, 8535Fairhaven, San Antonio, TX 78229. 512-690-8888.

FORSALE: USEDCROWNSA-2amp,M-600 mono amps, Dayton Wright Electrostatic speakers XG8-Mark 111. Call Jim(215) 322-6358.

MIDAS 24 into 10 stage monitor consolewith pro-4m modules, patchbay, twopower supplies, case. 1 year old, mintcondition. $22,000.00. (415) 529-2908.

PROFESSIONALAUDIO IN TUCSONCrown, Otari, Altee, Sound Workshop,AKG, MXR-Pro, dbx & more. Sales, design, service and demonstration showroom.Autograph ProAudio, 601E.Blacklidge Dr., Tucson, AZ, (602) 882-9016.

FOR SALE: (2) AKG 451-EB's with CK1Capsules, (2) AKG 414-EB's, (1) AKGBX1O, (1) Mellotron, (1) Farfisa VIP 345Organ. Contact Clay at: (516) 921-9421.

SELLINGSCULLY284B8 TRACK,Quantam QM128 12 x 8 board in-producer'sconsole,and miscellaneous.Makeoffer(s).(612) 253-6510.

Lexicon Prime Time: FOR IMMEDIATEDELIVERY. UAR Professional Systems,8535 Fairhaven, San Antonio, TX 78229.512-690-8888.

NAB ALUMINUM FLANGES. We manufacture 8", 10'/2",121/2",and14".Alsolargeflanges and special reels to order. Stockdelivery of assemblyscrews& nuts & mostaluminum audio, video, & computer reels.For pricing, call or write Records ReserveCorp., 56 Harvester Ave., Batavia, N.Y.14020.(716) 343-2600.



BUSINESS OPPORTUNITIES

AUDIO DESIGN & MANUFACTURINGENGINEERS-Do you want your ownbusiness? PUL TEC (Pulse Techniques,Inc.) will be available soon when ownerretires. (1411 Palisade Ave., Teaneck, NJ07666.

SERVICES

MAGNETIC HEAD relapping-24 hourservice. Replacement heads for professional recorders. IEM, 350 N. Eric Drive,Palatine, IL 60067. (312) 358-4622.

CUTTERHEAD REPAIR SERVICE for allmodels Westrex, HAECO, Grampian.Modifications done on Westrex. Quickturnaround. New and used cutterheadsfor sale. Send for free brochure: International Cutterhead Repair, 194 Kings Ct.,Teaneck, N.J. 07666. (201) 837-1289.

MULTI-TRACK RECORDING specialists-1-2-4-8-16-24 tracks, authorized dealerfor Tascam. Otari, Ampex. Teac, Technics, AKG, AB Systems, Crest. SAE Pro,dbx, Orban, Tapco C12, Audioarts, Loft.Lexicon. Ashly Audio, Altee. PAS. PSL,Shure. and many more. Single items orcomplete studio packages. Studio designand construction. Phone or write for aprompt written quotation. ProfeaalonalSound Laba, Inc., 42 N·orth Franklin St.,Hempstead, NY 11550. (516) 486-5813.

ACOUSTIC CONSULTATION-Specializing in studios, control rooms, discos.Qualified personnel, reasonable rates.Acoustilog, Bruel & Kjaer, HP, Tektronix,Ivie, equipment calibrated on premises.Reverberation timer and RTA rentals.Acou1Ulog, 19 Mercer Street, New York,NY 10013 (212) 925-1365.

CASSETTE DUPLICATION stereo ormono duplication. High quality cassettesat very economical prices. Spirit Recording, Box 656, West Bend, Wis. 53095.(414) 334-5510.

JBL AND GAUSSSPEAKER WARRANTY CENTER

Fast emergency service. Speakerreconing and repair. Compressiondriver diaphragms for immediateshipment. NEWCOME SOUND, 4684Indianola Avenue, Columbus, OH43214. (614) 268-5605.

WANTED

WANTED RECORDING EQUIPMENTmikes. recorders. consoles, outboardgear. Greg Field, Box 243, San Mateo, CA94401. (415) 343-1353.

WANTED: AMPEX MM1100 16-TRACKhead stack, remote control and spares.Also 16-track console MCI, Audiotronics,etc. in the $15,000 range. Dennis Reed,Box 50022, Palo Alto, Ca. 94303. (415)494-9344.

EMPLOYMENT

MATURE, QUALIFIED AUDIO ENGINEER for three to six month temporaryemployment .in Mexico City. Dutiesinclude instructing young recordingstudio engineers and studio techniques,plus consulting on studio related repair,troubleshooting and engineering problems. Other travel opportunities available.Excellent salary with interesting profitincentives. Contact Ron Newdoll, Accurate Sound Corporation, 114 5thAvenue, Redwood City, Ca., 94063, (415)365-2843.

SALESWe are an aggressive manufacturer ofpro audio products with an excellentreputation. We need an ambitiousprofessional to join us. Since we arethe standard by which others arejudged, we expect the most from oursalespeople. The candidate must begood at selling and able to prove itwith at least 2 years of recent experiencein sales of pro sound equipment. Weoffer top compensation and benefits,extensive travel in an 8-10 state areaand excellent prospects for a successful career. Please send resume to:

Dept. 91db Magazine

1120 Old Country RoadPlainview, NY 11803

An Equal Opportunity Employer M/F

Copies of dbCopies of all issues of db-TheSound Engineering Magazine starting with the November 1967 issueare now available on 35 mm. microfilm. For further information or toplace your order please write directly to:

University Microfilm, Inc.300 North Zeeb RoadAnn Arbor, Michigan 48106

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• AVAB America announces its move tonew and larger quarters. The facilities arelocated at 967 Howard Street, SanFrancisco, CA and will be used both forsales and manufacturing. Among theproducts being built there is a newsystem of modular dimmers. The firstcomplete permanent installation of thissystem is in the studios of KOKH-TVin Oklahoma City, OK. The dimmersare designed to complement AVAB'sline of computer-controlled and manuallight boards. AVAB is also manufacturing the FM 800, a production soundmixer for the motion picture and tele-vision industries.

• Audio-Technica U.S., Inc. has namedShane O'Neil to the position of directorof public relations. His primary responsibilities are for the planningand directing of all news media activitiesconcerning Aud io-Technica and itsproduct lines. In addition, he will beinvolved in advertising and sales promotion projects. Prior to joining A-T,O'Neil had been director of publicrelations and merchandising for aMilwaukee advertising and public relations agency and held a similar positionfor five years with Koss Corporation,a high fidelity component manufacturer.

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• Quantum Audio Labs, Inc., a LosAngeles based professional consolemanufacturer, has acquired AudioLogic-a spin-off of Uni-Sync, Inc.Audio Logic's operation will be consolidated into the Quantum Audio Labs'factory facility in Glendale, California.According to John Pritchett, Presidentof Quantum Audio Labs, Inc., sales andservice for both product lines will behandled out of the Glendale facilitywith Audio Logic operating as a whollyowned subsidiary of Quantum AudioLabs, Inc. Andrew C. Thompson, formerpresident of Audio Logic, has beennamed National Sales Manager forQuantum Audio Labs, Inc. and AudioLogic.

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Jlohn E. Volkmann

John E. Volkmann, a pioneer inthe field of room acoustics andelectroacoustics, died July 9, 1980 inPrinceton, New Jersey, after a shortillness. His professional careerspanned more than 50 years.

Mr. Volkmann was born inChicago, Illinois July 26, I905. Hereceived his BS (1927), MS (1928)and Professional Degree (I 940)from the University of Illinois.

He worked continuously withRCA in the field of acoustics,specializing in the development andapplication of large scale auditorium loudspeakers and stereophonic sound systems, as well as aconsultant on architectural, electronic and acoustic problems. Hecontributed to the solution ofinnumerable projects, includingstereophonic sound systems for theRadio City Music Hall, the Hollywood Bowl, the recording acousticsfor Walt Disney's Fantasia, customloudspeakers for the New YorkWorld's Fairs of 1938 and ll964-65and the Jones Beach MarinaStadium. He provided the acousticdesign for the RCA ltaliana's364,000 cu. ft. Studio A-regardedas the largest and first ever built forthe recording of full scale operas andsymphonic orchestras. He wasresponsible for the development and

design of the sound systems for theJohn F. Kennedy Center in Washington, D.C. He applied his pioneering concept of variable acoustics tothe design of the RCA VictorRecording Studios in New YorkCity.

For more than three decades,Mr. Volkmann was in charge of theadvanced acoustic development andtheater engineering activities atRCA Camden, New Jersey. In 1964he transferred to the RCA Laboratories, Princeton, New Jerseyas a member of the technical staff.He retired from RCA in 1970.

He has written numerous technical papers for scientific journalsand holds several U.S. Patents.

In 1962 he received the RCAAchievement Award for "Advancesin the Development of ArchitecturalAcoustics" and in 1967 the John H.Potts Memorial Award from theAudio Engineering Society for"Elegant Application of AcousticPrinciples in the Development ofLarge Scale Loudspeakers andSound Systems." He was a memberof honorary scientific fraternities,a Fellow of the Acoustical Society ofAmerica, the Audio EngineeringSociety and the Society of MotionPicture and Television Engineers.

Submitted by Harry F. Olson



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20,00Q~(:opies in print

8 clearly-defined sections·1a information-packed chapters

l. The BasicsThe DecibelSoundII. Tr:ansducers: Microphonesand LoudspeakersMicrophone DesignMicrophone TechniqueLoudspeakersIll. Signal Processing DevicesEcho and ReverberationEqualizersCompressors. Limiters and

ExpandersFlanging and PhasingIV. Magnetic RecordingTape and Tape Recorder

FundamentalsMagnetic Recording TapeThe Tape Recorder

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Fourth big printing of thedefinitive manual of recording technology!"John Woram has filled a gaping hole in the audio literature. This is a very fine book ... I recommend it highly.-High Fidelity. And the Journal of the Audio EngineeringSociety said, "A very useful guide for anyone seriouslyconcerned with the magnetic recording of sound."Sowidely read ... so much in demand ... that we've hadto go into a fourth printing of this all-encompassing guide toevery important aspect of recording technology. An indis-

pensable guide with something in it for everybodyto learn, it is the audio industry's first completehandbook on the subject. It is a clear, practical,and often witty approach to understanding whatmakes a recording studio work. In covering allaspects, Woram, editor of db Magazine, has provided an excellent basics section, as well as morein-depth explanations of common situations andproblems encountered by the professional engineer

V. Noise and Noise ReductionNoise and Noise Reduction

PrinciplesStudioNoiseReductionSystems

It's a "must" for every working professional ... forevery student ... for every audio enthusiast.

VI. Recording ConsolesThe Modern Recording

Studio ConsoleVII. Recording TechniquesThe Recording SessionThe Mixdown SessionVIII. AppendicesTable of LogarithmsPower. Voltage Ratiosand

DecibelsFrequency Period andWavelength of Sound

Conversion FactorsNAB StandardBibliographyGlossary

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