Parametric Equalizer Compressor/Limiter · DPX-200 Parametric Equalizer Compressor/Limiter Operating Manual ASHLY AUDIO INC. 847 Holt Road Webster, NY 14580-9103 Phone: (585) 872-0010

DPX-200

Parametric EqualizerCompressor/Limiter

Operating Manual

ASHLY AUDIO INC.847 Holt Road Webster, NY 14580-9103 Phone: (585) 872-0010

Toll-Free: (800) 828-6308 Fax: (585) 872-0739 Internet: www.ashly.com

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Operating Manual - DPX-200 Parametric Equalizer - Compressor/Limiter

1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 UNPACKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3 AC POWER REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4 MECHANICAL INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5 PARAMETRIC EQUALIZER CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.1 Equalizer Input Select Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.2 Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.3 Phantom Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.4 Shelving Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.5 Parametric Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.6 EQ Clipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45.7 EQ Master Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

6 COMPRESSOR/LIMITER CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56.1 Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56.2 Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56.3 Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56.4 Attack Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66.5 Release Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66.6 Output Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66.7 In/Out Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66.8 Threshold/Gain Reduction Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66.9 Input/Output Meter Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

7 CONNECTIONS AND CABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77.1 Balanced and Unbalanced Audio Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77.2 Inputs and Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77.3 Chain Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77.4 Compressor/Limiter Detector Loop/Ducking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

8 TYPICAL APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88.1 Parametric Equalizer Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88.2 Compressor/Limiter Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98.3 Special Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

9 DESIGN THEORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1110 BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1411 TROUBLESHOOTING TIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1412 WARRANTY INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1513 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1514 DIMENSIONS AND SCHEMATICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

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1. INTRODUCTION

The Ashly DPX-200 combines a four band para-metric equalizer and full function peak compressor/lim-iter in a single rack space product. Both equalizer andcompressor/limiter can be used as stand-alone processors,or can be automatically chained together with a back panelswitch.

Parametric EQ filters offer custom tailoring ofequalization solutions. Where a graphic EQ boosts orcuts fixed frequencies, a parametric EQ boosts or cutstunable frequencies. The DPX-200 parametric equalizeruses two tunable shelving filters along with two fully ad-justable, 20Hz-20KHz parametric filters, resulting in veryprecise control of frequency response.

The Ashly compressor limiter circuit was de-signed in response to the need for universal peak-sensi-tive automatic gain control (AGC) devices withexceptional audio performance and rugged durability.The result is a wide-bandwidth, ultra-low-distortion, lownoise VCA (voltage controlled amplifier) which is versa-tile and highly listenable.

Premium components are used throughout theDPX-200, and computerized automatic assembly equip-ment verifies that each component's electrical specifica-tions are within tight tolerances before becoming part ofthe circuit assembly. Each finished unit is then testedtwice before leaving the factory, guaranteeing you aworry-free, professional product for many years.

Please read this instruction manual thoroughlybefore operation so that you may realize all the featuresand benefits the Ashly DPX-200 has to offer.

2. UNPACKING

As a part of our system of quality control, everyAshly product is carefully inspected before leaving thefactory to ensure flawless appearance. After unpacking,please inspect for any physical damage. Save the ship-ping carton and all packing materials , as they were care-fully designed to reduce to minimum the possibility oftransportation damage should the unit again require pack-ing and shipping. In the event that damage has occurred,immediately notify your dealer so that a written claim tocover the damages can be initiated.

The right to any claim against a public carriercan be forfeited if the carrier is not notified promptly andif the shipping carton and packing materials are not avail-able for inspection by the carrier. Save all packing mate-rials until the claim has been settled.

3. AC POWER REQUIREMENTS

A standard IEC-320 AC inlet is provided on therear panel to accept the detachable power cord shippedwith the unit. Units distributed within the United Statesare preselected for 120VAC, 60Hz and should be pluggedinto a standard NEMA 5-15 3-wire grounded AC recep-tacle. Most units distributed outside the US arepreselected and labeled for 240VAC, 50-60Hz and areshipped with the appropriate power cord.

The DPX-200 will perform normally from 95 to125 volts AC. An internal line fuse is used. In the eventof fuse failure, refer to a qualified service technician forservicing. Power consumption is less than 20 watts.

WARNING:THIS APPARATUS MUST BE EARTHED

The exclamation point within an eqilateraltriangle is intended to alert the user to thepresence of important operating andmaintenance instructions in the literatureaccompanying the device.

The l ightning f lash with arrowheadsymbol, within an equilateral triangle, isintended to alert the user to the presenceof uninsulated "dangerous voltage"within the product's enclosure that may beof sufficient magnitude to constitute a riskof electric shock to persons. TO REDUCE THE RISK OF ELECTRIC SHOCK, DO NOT RE-

MOVE COVER. NO USER SERVICEABLE PARTS INSIDE.REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.

TO REDUCE THE RISK OF FIRE OR ELECTRICAL SHOCK,DO NOT EXPOSE THIS APPlIANCE TO RAIN OR MOISTURE.

TO REDUCE THE RISK OF FIRE, REPLACE ONLY WITHSAME TYPE FUSE. REFER REPLACEMENT TO QUALIFIEDSERVICE PERSONNEL.

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5. PARAMETRIC EQUALIZER CONTROLS

5.1 Equalizer Input Select SwitchThe DPX-200 equalizer input is selectable be-

tween line level or mic input, each with its own connec-tor. The line level input is used for normal signalprocessing, while the discrete mic input provides moregain for those applications where the DPX-200 is used asa comprehensive mic preamp. Press the input select switchin for line input, and out for mic input

5.2 GainA single knob, dual function gain control is used

for both mic and line inputs. When the mic input is se-lected, the gain range is from +20dB to +55dB. A -20dBpad switch on the back panel allows for nominal 0dB micinput level. When line level input is selected, the gaincontrol range is -∞ to +15dB. Unity gain for line levelsignal is 0.

5.3 Phantom Power+48V phantom power is provided to the mic in-

put XLR for use with condenser microphones. The phan-tom power switch is on the back panel, and a red LEDnear the power switch indicates that phantom power isturned on.

5.4 Shelving FiltersThe nature of a shelving filter is such that the fre-

quency response ramps up (or down) to a plateau and thenlevels off again, hence the term “shelf”. The DPX-200 hasa low and high shelving filter for general tone control orcorrection. Using the outer concentric knob, the calibratedfrequency tick-marks indicate the halfway point betweenunaffected signal and the frequency where the shelf flat-tens out. The inner concentric knob is the level control forthat filter, and indicates the decibel level of the flat portionof the shelf relative to the unaffected signal. The frequencyrange on the low shelf is 40Hz-400Hz, while the hi shelfrange is 1.6KHz-16KHz. Both filters have a ±15dB boostor cut, and can be switched in or out. A green LED turnson when the filter is engaged.

4. MECHANICAL INSTALLATION

The DPX-200 mounts in a standard 19 inch equip-ment rack. The mounting screw threads vary with differ-ent rack manufactures and you should refer to your rackinstructions for proper hardware. An oval head or flat headscrew with a plastic countersink washer is preferred toprotect the finish of the DPX-200 under the screw.

This unit is housed in a rugged steel case andwill tolerate moderate abuse. However, for road systemswhich may be dropped or otherwise subjected to extremeforces, we recommend some rear support for the chassisto prevent bending the front panel when these forces oc-cur.

For installations where it is desirable to protectthe front panel controls from tampering or accidentalmisadjustment, use the Ashly security cover. Installationis simple and does not require removal of the equipmentfrom your rack. See your Ashly dealer for details.

Ashly Security Cover Installation

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5.5 Parametric FiltersTwo 20Hz-20KHz parametric filters allow cus-

tom tailoring of EQ points, most useful for feedback con-trol, resonance compensation, or other types of frequencyspecific voicing. Each parametric filter consists of threemain controls, frequency, bandwidth, and level. Also, anin/out switch for each filter facilitates easier setups byallowing comparisons between filtered and unfiltered sig-nal. A green LED turns on when the filter is engaged.

Frequency: The outer concentric frequency con-trol determines the filter's peak frequency, or the pointthat is boost or cut. A peak filter, as the name implies,has a symmetrical rise and fall around the center fre-quency, as opposed to the plateau nature of a shelvingfilter. For maximum frequency resolution on the para-metric filter, a frequency range switch divides the cali-brated frequency labels by 10, meaning that if thefrequency control is set at 1K, and the range switch isthen pressed in, the frequency is now 100Hz instead of1KHz. Tick marks on the face panel are calibrated toISO 1/3 octave center frequencies.

Bandwidth: The inner concentric bandwidthcontrol determines how broad or narrow the peak filtercoverage is, and is expressed in octaves. For general tonecontrol, use a broader bandwidth. For notching out feed-back frequencies, use a narrower bandwidth. Being ableto optimize bandwidth for the job at hand is the mainreason parametric equalizers are preferred for notchingand feedback control.

Level: As with the shelving filters, the level con-trol boosts or cuts the frequency by up to 15 dB at thefilter peak.

5.6 EQ ClippingThe equalizer section has its own clip LED in

case both the EQ and comp/limiter are wired indepen-dently. All critical signal points within the parametricEQ are monitored for signal level which exceeds +19dBu.

5.7 EQ Master SwitchThe EQ master switch allows easy comparison

between filtered and unfiltered signal. A green LED nextto the switch turns on when the four filters are engaged.Note that the gain control is always active regardless ofthe setting of the EQ master switch.

6. COMPRESSOR - LIMITER CONTROLS

6.1 GainThe Gain control is used to adjust incoming sig-

nal level to the VCA circuit. It is always active, soswitching out the limiter function has no effect on thiscontrol. Used in conjunction with the input/output levelmeter display, this control is useful for setting up optimalsystem levels. This control should normally be left at"0" to achieve accurate threshold calibration.

6.2 ThresholdThe threshold control has a range of -40dB to

+22 dB, allowing applications from low level compres-sion to high level limiting. The threshold control de-termines the audio level above which gain reductionoccurs. When the threshold LED comes on, that meansthat gain reduction is beginning to occur, due to inputsignal peaks exceeding the selected threshold in dB.

6.3 RatioThis control determines the resultant change in

output level to changes in input level for all signals abovethreshold. The numbers printed around the ratio con-trol are calibrated in db and indicate the increase ininput (above threshold) required to produce a 1db in-crease in output. This can be expressed conveniently asa ratio. If the output remains constant no matter how highthe input level, we have an infinite (∞) input/output ra-tio. It should be remembered that the ratio control has noeffect on signals which are below threshold.

There is a common but incorrect notion that lim-iting always implies the use of an infinite ratio. Althoughthere are times when an infinite ratio is desirable, therewill be situations where infinite, or “hard”, limiting ac-tion is neither appropriate nor necessary. In fact, it should

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be noted that an infinite ratio setting is likely to causenoticeable side effects in the sound, and may not be us-able on programs where subtle control is desired.

6.4 Attack TimeThe response of the compressor/limiter to signal

levels above threshold is further defined by the attack timecontrol. Attack time is the amount of time it takes toattenuate the output level after threshold has beenreached. For very fast transients, such as hand claps, snaredrums, or other percussive sounds, a fast attack time isusually desirable so that the limiter can respond in timeto control the peak level. On other types of program ma-terial, a slower attack time may be preferred. An abruptattack may, on some material, “square off” the top of awaveform, producing a distorted sound. The DPX-200 pro-vides continuously variable attack times from 200 micro-seconds to 20 milliseconds.

6.5 Release TimeAnother parameter which affects compressor/lim-

iter performance is release time, or the time required torestore system gain to normal after the input signalhas fallen below threshold level. Again, proper releasetime will depend on the type of program material beingprocessed and the way in which the limiter is being used.

When subtle limiting is desired, slow releasetimes are often chosen to avoid condition referred to as“pumping” or “breathing”. This occurs when overall gainis modulated up and down by repeated peaks which arefollowed by quieter intervals. If the release time is settoo fast, then the overall level will jump up and down,producing an objectionable and unsettling effect. Notethat, in some cases, an individual track or channel whichseems to be pumping may sound acceptable when heardin context of a complete mix.

A unique feature of all Ashly compressor/limit-ers is the incorporation of a double release-time con-stant. When a conventional compressor/limiter is adjustedfor slow release times, transients such as mic “pops” maycause a severe reduction in gain followed by a slow fade-up, making the action of the limiter very obvious. With

the double time constant, release from gain reduction af-ter a brief transient is always fast, with a slower releaseafter a sustained overdrive.

6.6 Output LevelOutput level control is provided to fully cut or

restore up to 18 dB of system gain. For unity gain, setthe control to 0. NOTE: When the compressor/limiter isswitched out, the output control still functions.

6.7 In/Out SwitchThis switch enables you to quickly hear the com-

pressor/limiter in or out of the audio chain. When theswitch is in the out position, all limiting and compres-sion controls and functions are bypassed, with the excep-tion of the gain and output controls, which continue tofunction as straightforward level controls.

6.8 Threshold/Gain Reduction DisplayAs soon as the threshold level is reached, the yel-

low LED illuminates. Depending on how far the inputlevel rises above threshold, successive red LED’s will il-luminate, indicating gain reduction. Gain reduction canbest be described as the difference between input leveland the resulting change to output level. For signalsbelow threshold, there will of course be no gain reduc-tion, that is, a 10dB increase in input will yield a 10dBincrease in output. For signals above threshold however,output level will increase only to the extent that the ratiocontrol allows. With a high ratio, say 20 or so, it will take20dB of increased input level to increase output level by1dB. With a gentler ratio of 3:1, input signals abovethreshold will be “gain-reduced” at the output by 1/3. Inother words, with threshold set at 0dB, a signal peak at+12 dBV that is 3:1 compressed (ratio at 3) will produceonly +4 dB (12÷3) at the output, and 8 dB of gain reduc-tion has occurred (12 dBV input minus 4 dBV output=8dB reduction.)

6.9 Input/Output Meter SelectWhile the gain reduction display accurately rep-

resents the action of the limiter, comparing input to out-put levels in real time is somewhat more intuitive, and ismade simple using the input/output meter select switch.

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The input meter takes its signal just after the gain con-trol, and will indicate input signal level regardless of out-put levels or limiter settings. The output meter displaytakes its signal from the actual output of the unit, so ev-ery control that affects the output will also have an effecton output meters. Used in conjunction with the gain re-duction meters, input/output meters prove to be an ex-tremely useful diagnostic tool when working with systemdynamics and level control.

7. CONNECTIONS AND CABLES

7.1 Balanced and Unbalanced Audio ConnectionsBalanced signal connections are preferred in pro

audio applications because of their improved immunityto induced hum and noise. A properly shielded and wiredbalanced input stage on any audio product will reject mostunwanted noise (RFI, EMI) picked up by the cable, aswell as minimize ground loop problems. Therefore it isalways advantageous to use balanced connections whenrunning signal more than ten or fifteen feet, although par-ticularly noisy environments may require that even shortpatch cables be balanced.

Unbalanced connections are used mostly for shortdistance, high level signals (0dBu nominal). Most exter-nal EMI noise pick-up will bemasked under the noise floor of thesignal, assuming there is little or nogain following the unbalanced signal.If a gain stage does follow a signal,or if externally sourced noise per-sists, use balanced connectors.

7.2 Inputs and OutputsThe DPX-200 uses two dif-

ferent audio connector types. 1/4"TRS (tip-ring-sleeve) phone jacks,and three pin XLR connectors will al-low interfacing to most professionalaudio products. Ashly TRS balancedconnections use the tip as (+) and thering as (-) signal, with sleeve used forground. Ashly XLR connectors usepin 2 (+) and pin 3 (-) with pin 1

ground. Inputs are 20KΩ active balanced using preci-sion 1% metal film resistors, outputs are 200Ω "pseudo-balanced", which means they have balanced impedancewith a single-ended signal source, and can be wired bal-anced or unbalanced. When possible, we recommendbalanced connections between all components in yoursystem.

If inputs are used unbalanced, the signal shouldbe on the (+) connection and the (-) connection must betied to ground, or signal loss will result. While a monophone plug used as an unbalanced connection will auto-matically ground the (-) ring of the jack, XLR's will notautomatically do this, so attention must be given to properwiring.

7.3 Chain SwitchThe chain switch on the back panel allows the

output of the parametric equalizer to be fed directly tothe input of the compressor/limiter, with no external cablerequired. When the chain switch is in, the input connec-tors to the compressor/limiter are removed from the cir-cuit, while the equalizer outputs remain functional.

7.4 Compressor/Limiter Detector Loop - DuckingThe DPX-200 com-

pressor/limiter has a TRS In-sert DETECTOR PATCHpoint which can be used as a"ducking" input, or in con-junction with an equalizer toproduce frequency-sensitivelimiting. Various uses of thedetector patch are discussedunder TYPICAL APPLICA-TIONS.

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8. TYPICAL APPLICATIONS

By itself, a parametric equalizer is useful for gen-eral tone control, feedback control, room resonance cor-rection, individual microphone voicing, and many otherapplications. The compressor/limiter provides many so-lutions where dynamic signal level processing is required.The combination of a parametric EQ and a compressor/limiter allows for additional applications, such as a fullrange speaker processor, 70 volt distributed system pro-cessor, mixing console channel insert, and frequency sen-sitive limiting, just to name a few. In most cases, theDPX-200 should be the last device before the power ampor crossover, or right before a recording device or trans-mitter.

8.1 Parametric Equalizer Applications

General Tone ControlLike a graphic EQ, the parametric equalizer is a

very useful device for general tone shaping because thefilter’s center frequency, bandwidth and level are all con-tinuously variable. To use the power of the equalizer ef-fectively, you need to translate your idea of the tone youwant to produce into a range of numerical frequencies.This is simple after a little practice. Here are a few refer-ences which are useful for starting points:

- Very low bass (the “wind” in a kick drum, almost feltas much as heard -40Hz-80Hz.

- The low register of a male voice - 200Hz

- The low register of a female voice - 350Hz

- Lower midrange (“warmth” frequencies) - 400Hz-1KHz

- Upper midrange (“harshness”, snare drum “bite”, “hot”sound) -2.5KHz-4KHz.

- Sibilance (“sss” sounds, cymbal “sizzle”) - 8KHz-15KHz.

Try using these starting points as a guide whenyou want more or less of these types of sounds. Adjustby ear from there. It is always a good idea to rememberthat a little equalization usually works out much betterthan a lot, and that there are many audio problems whichcannot be solved with equalization alone.

Feedback ControlThe parametric equalizer is a powerful tools when

applied to eliminating feedback problems. On a tradi-tional graphic equalizer, the fixed filter center frequen-

cies are insufficient when the frequency of feedback oc-curs between two slide faders, or is extremely narrow.The continuously variable center frequency and bandwidthof a parametric equalizer allows very sharp notching offeedback frequencies.

The following procedure outlines how to use aparametric equalizer to suppress feedback frequencies:

1. Start with all the EQ switches out except themaster EQ switch in and the gain at 0.

2. With the entire PA hooked up and turned on,slowly increase the sound level at the mixer untilfeedback is heard, then lower the level by about3 dB so that feedback does not continue.

3. Start with one of the two parametric filters bysetting the level at 0, bandwidth set fairly sharp(about .3 oct.), and adjust the frequency controlto where you estimate the predominate feedbackfrequency to occur.

4. Push in the filter’s EQ switch and increase itslevel control by about +6 dB. Now “sweep” thefrequency around where you have estimated thefeedback frequency until feedback occurs. Onceyou have induced the feedback by boosting itsfrequency, quickly turn down the filter’s levelcontrol to about -6 dB to suppress or “notch out”the feedback frequency.

5. Again slowly increase the master level at themixer until feedback is heard. If a new feedbackfrequency is heard, then repeat step 3 with theother parametric filter to find and suppress thenew frequency. If the original feedback frequencyis still heard, then adjust the first filter’s leveleven lower. The bandwidth control may be ad-justed full clockwise to produce a very sharpnotch so that a severe feedback frequency can beattenuated by as much as 15 dB without degrad-ing the frequency response with noticeablenotches. Note: Very sharp bandwidth lowers themaximum equalizer input level because of thehigh filter gain necessary to obtain such a nar-row bandwidth. Only use bandwidth control fullCW (.05 Octave) in severe cases.

Console Channel EqualizationMany mixing consoles provide only simple equal-

ization for individual channels. If your console has chan-nel inserts, you can patch your parametric equalizer into

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a channel that’s being used for something important anduse it to tailor the sound of this channel exactly the wayyou want.

Large Room EqualizationLarge rooms tend to suffer from multiple reflec-

tions with long time delays, long reverberation times, and“ring-modes”, all of which lead to reduced intelligibilityand a generally “muddy” sound. As sound travels longdistances through the air, high frequencies are attenuatedmore than low frequencies. In general, large rooms ben-efit from some low frequency roll-off, high frequencyboost, and attenuation of ring mode frequencies.

8.2 Compressor - Limiter ApplicationsAs the functional name implies, a compressor/

limiter can be divided into two basic categories, limitingand compressing. When used as a protective device toprevent audio levels from overloading systems such astape recorders, power amplifiers, speakers, or transmit-ters, it is generally referred to as a limiter.

It may also be used to create special effects andunusual sounds for recording and musical performanceby deliberately reducing the dynamic range of a signal,creating a much louder or fuller sounding signal withoutincreasing the loudness peaks, in which case it is referredto as a compressor.

The Limiter As A Protective DeviceThe DPX-200 compressor/limiter section pro-

vides fast and accurate gain control for the prevention ofsound system overload due to unexpected transients.Sound system distortion is usually the result of amplifi-ers running out of power, in which case nice round wave-forms turn into harsh sounding squared-off waveforms.Looking at it from the perspective of the speaker dia-phragm, this means that, whereas in normal operation thediaphragm is required to accelerate, slow down, smoothlychange direction, and accelerate again, distorted opera-tion requires an instant acceleration, instant stop, a changeof direction, and instant acceleration again.

Since speaker diaphragms are subject to the lawsof physics, they won’t take this kind of punishment forlong. The diaphragm may shatter, or its voice coil mayoverheat. In addition to the damaged caused by sustainedoverload, the speaker may also be damaged by occasional,one-shot high level overload, for example, the sound of amicrophone falling face-first onto a hardwood floor. Evenif this type of transient doesn’t destroy a speaker outright,it may damage the speaker surround in such a way as tocause mechanical abrasion and future failure.

Alternatives For Sound InstallationsTo install a compressor/limiter in a sound sys-

tem using a passive crossover, insert it between your mix-ing console output and the power amplifier input. Forsystems using electronic crossovers, there are two waysto use a compressor/limiter. It may be inserted betweenthe mixer output and the crossover input, in which case itwill act on the entire audio frequency spectrum. Alter-nately, if the limiter is inserted between an output of theelectric crossover and the input of a power amp, it willonly affect a specific band of frequencies.

RecordingThe Ashly limiter can be used to prevent tape

saturation in analog recording. Also, with modern trendstoward inexpensive digital recording, it remains neces-sary to protect against input overload. With digital re-cording, the information stored on tape, hard disk, opticaldisk, etc., is either a 1 or 0, so actual signal level on thetape is not the concern it is with analog recordings, infact it is not even a user controllable parameter. What isof concern however, is the signal level applied to the A-D(analog to digital) converters. If clipping occurs at theconverter input stage, the resulting distortion is most un-pleasant, and will be recorded digitally as if they werepart of the original audio signal, forever mixed with theaudio. To prevent converter distortion while preservingthe extended dynamic range of digital recording, look upthe max input level of your recorder/converter and set upthe limiter as follows:

1. Set Gain to 0.2. Set Threshold to 2-3 dB below max converter input.3. Set Ratio to 10.4. Set Attack to 2 mS.5. Set Release to .2 Sec.6. Set Output level to 0.

If you are exceeding threshold frequently, yourinput signal is probably too high and should be turneddown. Of course, every situation is different, so experi-mentation before final recording is always a good idea,but this is a good starting point.

To obtain a gentler limiting action at the expenseof some dynamic range, decrease the threshold to -15 andthe ratio to 3-5. This is also a good starting point foranalog recording.

10


BroadcastingCompression has long been used as a tool

to make an audio signal appear louder. Agood example is in broadcasting, wherecompeting stations with identical transmit-ters and power attempt to sound louder thaneach other. Since they are all restricted with

respect to maximum audio level (modulation), their besttactic is to squeeze the dynamic range of their programsto just a few dB. The audio output level of the stationvirtually never changes, and the listener perceives thiscontinuous high-level sound as being louder than the samematerial in an uncompressed form. Although both com-pressed and uncompressed programs reach the same peaklevels, the compressed signal stays near peak level moreof the time, and thus sounds louder. This technique makesthe broadcast more intelligible over ambient noise, andincreases the geographical area over which the broadcastis audible to the listener. Additionally, this compressiontechnique is extremely useful for FM and infrared trans-mission systems for the hearing impaired.

8.3 Special Effects

Compression For Feedback ControlA common ritual in sound system set-up is equal-

izing the room to remove feedback. This is generallyaccomplished by turning up system gain to purposely in-duce feedback, searching for the center frequency of thefeedback, and then equalizing at that frequency to removethe feedback. Once this frequency has been cut, systemgain is again increased to induce another feedback point,and the whole procedure is repeated until the engineer issatisfied that the significant problem frequencies havebeen corrected. The major problem with this approach isthat the feedback can easily get out control, and the engi-neer ends up dashing back and forth between the mixervolume controls and the equalizer controls, while every-one in the room plugs their ears and prays it will endsoon. The Ashly DPX-200 can turn this procedure into afast, painless job, eliminating loud feedback levels andthe possibility of speaker or ear damage.

Procedure:1. Set up the DPX-200 limiter controlsas follows:

a. Output level control to -20dB.b. Input Gain control to 0dB.c. Threshold control to -30dB.d. Ratio control to infinity (∞)e. Attack time to 5mS.f. Release time to 1 Sec.g. Limit switch IN

2. Using a 1/3 octave (31 band) or parametricequalizer, set the EQ controls to a flat setting, and if theequalizer has an overall volume control, boost it by 10 to15 dB.

3. Open up several microphone input channelsto a normal operating level, with typical EQ settings, andturn the console master fader up to a louder than normalsetting. At this point, the system should be well into feed-back, but the room volume will be constant due to theaction of the limiter. You can listen to the feedback atany level you like by simply varying the limiter outputlevel control, although below a certain monitoring level,the feedback will stop.

4. Try to determine the feedback frequency, andthen equalize it by adjusting the center frequency, band-width, and boost/cut controls of your parametric equal-izer. (Note: a graphic equalizer can also be used, althoughwith less accuracy.) After eliminating the problem fre-quency, try to further define it by sharpening up the band-width, reattacking the frequency control, and making thecut shallower, if possible.

5. As soon as the first feedback frequency hasbeen removed, the compressor/limiter will automaticallybring up system gain until another feedback point is in-duced. Repeat the equalization procedure until it becomesimpossible to distinguish individual, predominant feed-back frequencies.

6. Write down EQ marks for safekeeping if nec-essary, and return all mixer, EQ master gain, and com-pressor/limiter gain controls to normal operationalsettings.

Altering the Texture of Musical InstrumentsIt would be impossible to mention here all the

ways that compression is used to create new sounds withfamiliar instruments. Some typical uses are:

1. Creating a “fatter” kick drum or snare sound.2. “Thickening” acoustic guitars.3. Adding punch and sustain to electric bass orguitar.

In general, use a gentle compression ratio, say4:1, with a 10 mS attack time, 0.1 Sec. release time, anda low enough threshold to cause 6 to 10dB of Gain Re-duction. Try using this effect to help bring out a leadvocal or instrumental solo in a cluttered mix. The com-pressor is also a great corrective tool when working with

11


singers whose own dynamic control is less than perfect.A little compression helps to keep their quieter lines frombecoming buried in the mix. Experimentation is highlyrecommended.

Voice-Over Compression (“Ducking”)The compressor/limiter can be used to automati-

cally reduce music to a background level when an an-nouncer is speaking. In this scheme, only the music signalis actually gain-reduced by the limiter. However, the de-tector is connected to respond to an announcer’s voiceinstead of the music’s peaks. Voice-Over compressionassumes you are already using some sort of mixer to com-bine the music and mic signals. Use the direct out (send)of the mic channel to feed the detector input on the DPX-200. Note: Be sure to use a mono plug for the detectorinput. Then use the Threshold and Ratio controls to de-termine when and by how much the announcer’s voiceaffects the music level.

De-EssingA special type of saturation problem often en-

countered in recording is the sibilant (Ssss) sound of thehuman voice. High frequency, sibilant sounds can reachvery high energy levels, so that a voice that is otherwiseundistorted breaks up on the esses, producing a raspy, un-desirable sound. With analog recording to magnetic tape,high frequencies tend to saturate the tape sooner, and com-bined with the internal high frequency boost (record pre-emphasis) on standard tape decks, the need to controlsibilants becomes apparent.

The solution is frequency-dependent limiting,which is easily accomplished with the DPX-200. By in-serting an equalizer into the Detector Patch point andboosting the equalizer at high frequencies in the vicinityof the sibilant, the limiter’s detector circuit becomes moresensitive to this particular range of frequencies, and sowill limit the bothersome sibilants more than other fre-quencies.

Realize that this technique is very different fromsimple equalization. Equalizing a sibilant vocal by cut-ting high frequencies would result in a loss of importanthigh frequency information at all times, whereas de-essinghas no effect whatsoever on the signal except at the in-stant of the sibilant. At that moment, the Ashly limiterwill reduce overall gain. Frequency response is unaf-fected, and the sibilant is controlled.

9. DESIGN THEORY

Parametric EqualizersThe hear t of Ashly parametric equalizers is a

unique bandpass filter circuit. Basically a “state-variable”type, this filter is trimmed and optimized to provide excel-lent transient response and a wide range of frequency andbandwidth adjustment. Each filter can be tuned over a 100:1frequency range (about 6.6 octaves) and a 70:1 bandwidthrange with no more than a 2 dB amplitude error at centerfrequency. At its sharpest setting, the filter has a “Q” ofabout 35 and generates a response curve with 3 dB pointsonly 1/20 octave apart, making feedback control possiblewith no audible side effects. Each filter is placed in the feed-back loop of a summing amplifier to produce the desiredfrequency response. Since a separate summing amplifieris used for each band, no interaction between bands oc-curs.

Compressor/Limiters: The Need For Gain ControlThe human ear excels in its ability to detect an

extremely wide range of loudness levels, from the quiet-est whisper to roar of a jumbo jet. When we attempt toreproduce this dynamic range, by means of amplifiers,tape recorders, CD players, or radio transmitters, we runinto one of the fundamental limitations of these electronicmedia: limited dynamic range. Amplifier dynamic rangeis quite good, and is adequate for most musical programmaterial. However, some types of audio equipment, suchas cassette tape recorders, have a very narrow useful dy-namic range.

What is it that compromises the dynamic rangeof this equipment? The useful operating region of a pieceof audio equipment is squeezed in between noise and dis-tortion. As program level decreases, it approaches whatis known as the “noise floor”, and if the volume of theprogram material goes lower still, it is engulfed by thenoise. The noise floor, or minimum constant noise level,will consist of hiss, hum, transistor noise, tape hiss, buzzand whatever noises are inherent in the medium. Whenthe program level is considerably higher than the noisefloor, our hearing masks the noise, and it is not a prob-lem. However, when listening to very quiet sections of aprogram for example, a pause between movements of astring quartet the noise can become very bothersome.

At the other end of the loudness spectrum, thelimitation on dynamic range is usually distortion, eitherin the form of amplifier overload, tape saturation, or A toD clipping. In most transistorized equipment, the transi-tion from clean, undistorted operation to severe distor-tion is very abrupt. Therefore, it is common practice tooperate a piece of equipment at a level that is somewhatbelow the distortion point, leaving a margin of safety for

12


The quietest portions of the original signal will be effec-tively increased in volume while the loudest portions ofthe original signal will be decreased. In effect, both endsof the dynamic spectrum will be pushed toward the“middle”. This is quite different from simple limiting,where only loud peaks are subjected to gain reduction.More than anything else, it is this double-ended effectwhich distinguishes compression from limiting. Com-pression is further differentiated from limiting by care-ful selection of attack and release times. When limitingis employed to protect an audio system against transientvolume peaks and possible overload, attack time is usu-ally set as fast as possible, consistent with distortion-free performance. Release time would also be relativelyshort, so that the output signal would be restored to nor-mal as quickly as possible after the transient.

Compression is frequently used to keep over-all signal level within a specific dynamic range, andfor this application, slower attack and release timesare usually chosen. This approach is analogous to ourmanual gain riding example, where our operator is fad-ing the music up and down to keep it fairly constant,but is doing it slowly enough so that the listener is un-aware that the gain is being altered.

Voltage Controlled AmplifiersEarly VCA’s were based on vacuum tubes with

a “remote cutoff” characteristic. The tube would sim-ply change its gain in response to a changing bias volt-age. Tubes developed for this purpose did an excellentjob, in fact they could exceed the noise and distortionperformance of today’s best solid state VCA’s. Unfor-tunately, they also had some serious disadvantages pe-culiar to tubes - change of gain and matching as agingtook place, heat, microphonics, high cost, and the needfor both high-voltage and filament power supplies.

Over the years the need for good, low-cost,solid state VCA brought about many innovative ap-proaches. A good example is the electro-optical at-tenuator where a photocell is used as one leg of apotentiometer. Since the photocell behaves as a trueresistor, distortion and noise are very low. Unfortu-nately, the response time of photocells is slow and un-predictable so their use in a fast peak-limiter is reallynot feasible. Also, the matching between units is verypoor so that stereo tracking is not possible without te-dious hand-matching of photocells.

Another approach uses a field-effect transis-tor (FET) as a variable resistor. Here, at least, the re-sponse time is fast (in the nanosecond range), butmatching between units is still poor, requiring handmatching for stereo. An additional problem is that a

unexpected, transient volume peaks in the music. Thissafety margin is known as headroom, and may range from10 to 25 dB. Lowering our standard operating level to leaveourselves some headroom helps prevent distortion, but atthe same time it moves our average program level closerto the noise floor, thereby compromising signal-to-noiseperformance. It becomes apparent that to get most out ofan audio system, you have to keep your standard operat-ing level as high as possible without risking distortion.

Gain RidingOne solution to the noise vs. distortion trade-off

is to keep your hand on the level control and manuallyadjust gain to suit the program. Indeed, there are timeswhen this approach is entirely satisfactory. However, inmost types of music there are instantaneous, short dura-tion volume peaks, or transients, which would be difficultto anticipate and impossible to respond to with manualgain riding, you simply could not bring the level downfast enough. In many situations, this can present real prob-lems. For example, in recording, an extra burst of enthu-siasm from a lead singer might overload the capabilitiesof your recording tape, causing ragged distortion and ne-cessitating another take. In sound reinforcement, a sud-den burst of energy through the system can blow fuses oreven damage loudspeakers.

In addition to the problem of response time withmanual gain riding, it also requires your constant atten-tion, which takes you away from more important jobs. Theneed for a fast-acting, reliable, automatic gain control isanswered by limiters and compressors.

What Compressors and Limiters Do

LimitingIn any musical program are constant changes in

loudness. It is the job of a limiter to detect when the vol-ume has exceeded a predetermined maximum safe level,and to then turn down the volume. When the incomingsignal returns to its original level, the limiter should re-spond by restoring the gain to normal. Thus, when thelevel is within a specified “safe” range, the limiter has noeffect. When an occasional peak occurs, the limiter re-sponds. This situation is completely analogous to manualgain riding, except that it occurs faster and more consis-tently.

CompressionA very significant difference in dynamic range is

achieved simply by changing the relationship between nomi-nal signal level and threshold, as a result of either increas-ing the GAIN and/or decreasing the THRESHOLD control.The most interesting effect to be noted, however, is seen bycomparing the original input signal with the output signal.

13


FET will only act as a pure resistor with very small sig-nals applied so it is necessary to attenuate an input signalbefore the gain control FET and then amplify it again.Of course this results in less than ideal noise performanceand imposes a frustrating trade-off: less noise = more dis-tortion.

A number of VCA’s based on the exponential volt-age-current characteristic of a bipolar junction transistorhave been used. One of the most common is called a“transconductance amplifier”. Using the inherent match-ing obtained by integrated circuit technology, these de-vices have very predictable control characteristics.Tracking within 1dB over a 40dB range is common. Notonly do the control characteristics match well from unitto unit, but they can easily be made exponential (loga-rithmic) so that even increments of control voltage pro-duce even increments of gain change in decibels. Theresponse time is also very fast.

The problem with simple transconductance am-plifiers is that, like FET VCA’s, they can handle only verysmall signals so the noise performance is poor. A num-ber of linearizing circuits have been devised to minimizethis problem, but even the best transconductance amplifi-ers have an equivalent input noise of about -80dBv, whichcompares poorly to straight linear amplifiers.

The best analog compromise to date is the “classAB current ratio multiplier.” Early implementation ofthis circuit used two matched pairs of transistors, one pairof NPN’s and one pair of PNP’s. The problem here isthat excellent matched integrated NPN pairs were avail-able, but integrated PNP’s were not. The PNP’s had to behand-tested and matched. Careful trimming was neces-sary for low distortion and even minor temperaturechanges made re-trimming necessary because of differ-ing characteristics between the two types.

The Ashly VCAThe Ashly VCA is an integrated current ratio mul-

tiplier circuit. It has low noise (-90dBv), low distortion(.05%), excellent response time and tracking and doesnot suffer from thermal drift. The noise and distortionare at state-of-the-art levels and the circuit is consistentin mass production with minimal trimming and no hand-selection of transistors.

DetectorsIt would seem that, of the two components in a

compressor/limiter, the VCA is the more critical since theaudio passes through it and the detector only provides itwith a control voltage. Experience showed us that both arecrucial to the overall sound and that, if anything, thedetector’s performance is the harder to judge by conven-

tional measuring techniques. While the VCA is doing itsjob if it has low noise and distortion, the detector must con-stantly adjust the gain of the audio path in a manner whichkeeps the level under control while sounding acceptable tothe listener. This constantly changing gain is a dynamicaction, while conventional audio measurements like noiseand distortion checks are Static (at a constant level). Webecame painfully aware of this problem with some of ourearlier limiter prototypes which measured fine and soundedterrible. This led us to use a purely subjective approach inthe design of the detector - we did a lot of listening to de-termine what sounded good and what didn’t.

Two important features emerged from this re-search:

1. We designed the detector to let the attack andrelease times speed up as more and more limiting occurs.The compression ratio also increases. This lets us main-tain peaks fairly close to a constant ceiling level, but al-lows the illusion of increasing loudness as input levelincreases, thereby preventing complete loss of dynamicswhen limiting.

2. We incorporate a double release time constant.When release time was set slow with a single time con-stant, transients such as mic “pops” caused a quick re-duction in gain and a slow fade-up, making the action ofthe limiter very obvious. With the double time constant,release from gain reduction after a brief transient is al-ways fast, with a slower release after a sustained over-drive.

When choosing a compressor/limiter, you can seethat it is very important to listen to it in your particularapplication and see that it sounds the way you want. Thereare lots of these devices with seemingly excellent specswhich sound very different with real program materialapplied to them.

Peak Or RMSThere are several ways of looking at a signal to

determine its level. A peak detector looks at the maxi-mum voltage a signal reaches regardless of it’s waveform,while an RMS (root mean square) detector looks at theenergy in a signal regardless of the short term voltagelevels. This makes a peak detector the correct choice forpreventing clipping, overmodulation, or tape saturation,while an RMS detector can be used to restrict material toa given loudness. When an RMS limiter is used to pre-vent clipping, the result is unpredictable. For instance, aflute and a snare drum which are limited to the same RMSlevel might have peak levels as much as 30dB apart! Usepeak limiters to prevent clipping.

14


10. BLOCK DIAGRAM

11. Equalizer Troubleshooting Tips

No Audio Output

Check AC power - is the pilot light on?Check in/out connections - are they reversed?Are you sure you have an input signal?Is the correct input selected?Is the gain control turned all the way off?

EQ Controls Do Nothing

Is the individual filter or master EQ switch in?Is the bandwidth set too narrow to be heard?The lowest and highest frequency filters may be

beyond the range of the program material or speakers andmay produce little or no audible effect.

Peak Light Flashes or Stays On All the TimeIf the peak light flashes, the signal level to the

equalizer is too high, or a particular filter is boosted toomuch. Turn down the gain or switch the EQ filters. If itis on all the time, disconnect the input and output cables.If it is still on, the unit must be returned for service.

Distorted Sound

This will only be caused by too much signalwhich will show on the Clip LED. If the LED is notflashing, there is an overload within another productin the signal path. Adjust the relative gain of eachcomponent in your chain to keep everything at a com-fortable level.

Excessive Hum or Noise

Hum will usually be caused by a ground loopbetween components. Try using the suggested bal-anced input and output hook-ups if the other piecesof equipment used in conjunction with your equal-izer have balanced inputs and outputs.

Noise (excessive hiss) can be caused by in-sufficient drive signal. Make sure you are sending anominal 0 dBu line level signal to the equalizer. Mostnoise problems occur because gain is applied to au-dio signals too late in the chain. For best performance,apply gain to individual source signals as early aspossible, like at the mixer input preamp section. Asgain increases, it also boosts the noise content of thatsignal. Any cumulative noise built up in a mixed sig-nal will only be increased by using an equalizer as again device, so make every attempt to operate theequalizer with as little gain as possible.

Note: Unshielded cables, improperly wired con-nectors, and cables with broken strands of wire are verycommon problems. Use quality cables with quality, cor-rectly wired connectors.

11.1 Compressor/Limiter Troubleshooting Tips

No Output

Check AC power. Is the power switch on? Checkinput and output connections - are they reversed? Areyou sure you have an input signal?

Controls Have No Effect

Is the limiter in/out switch in? Perhaps the ratiocontrol is set too low to produce an audible effect or theinput level is below threshold. Is the threshold LED light-ing up? If not, lower the threshold setting or increase thegain. Do not expect to hear any effect when the inputlevel is below threshold, since the unit is simply a linearamplifier at those levels.

-

++

-

-

++

-

-

++

-Individual EQ Band In/Out

EQ Master In/Out

OUTPUT

DPX-200 Block Diagram

Mic

Line

(4)(3)(2)(1)

PARAMETRIC EQ4 BAND

LINE

MIC

CHAIN

LIMITER

LIMITER

EQ OUTPUT

GAIN

3

3

2

2

1

1

CHANNEL

INSERTDETECTOR

CLIP

CLIP

TH

3

3

3

2

2

2

1

1

1

IN/OUT

GAIN REDUCTION DISPLAY

THRESHOLD

RELEASE

ATTACK

RATIO

CIRCUITDETECTOR

INPUT

INPUT

INPUT

GAIN

LEVELOUTPUT

INPUT/OUTPUT METERS

VCA

15


When Using Heavy Compression, Background Noise Is Noticeable During Quiet Sections Of The Program

As defined in the section on compression, quiet program material is effectively made louder while loud peaksare made quieter. When the program source is thus raised in volume, its noise floor is also raised in volume by aproportionate amount. This is not a defect in the compressor/limiter, but an unavoidable side effect of the gain alteringprocess. If the noise becomes a problem, the solutions are to either decrease noise at the program source, or use lesscompression.

Excessive Hum Or Noise

Hum is often caused by a “ground loop” between components. Try using the suggested balanced input andoutput hookups if the other pieces of equipment used in conjunction with the DPX-200 have balanced inputs andoutputs. Noise can also be caused by insufficient drive levels. Make sure you are sending a nominal 0 dBV line levelsignal to the unit.

12. WARRANTY INFORMATION

Thank you for your expression of confidence in Ashly products. The unit you have just purchased is protectedby a five-year warranty. To establish the warranty, be sure to fill out and mail the warranty card attached to yourproduct. Fill out the information below for your records.

Model Number ___________________________ Serial Number ___________________________________

Dealer ________________________________ Date of Purchase ___________________________________

13. SPECIFICATIONS - Parametric EQ:

Input Connection, Line in . . . 1/4" Phone Jack, XLR 20KΩ Active Balanced

10KΩ UnbalancedGain, Line input . . . . . . . . . . . - ∞ to +15dB

Input Connection, Mic in . . . . Low Z Balanced XLRMic Input Pad Attenuator . . . 0dB out / -20dB InGain, Mic input . . . . . . . . . . . . +20dB to +55dB

Shelving Filter Frequency Range (midpoint of slope)Low . . . . . . . . . . . . . . . . . . . . . . 40Hz-400HzHigh . . . . . . . . . . . . . . . . . . . . . 1.6KHz-16KHzShelving Filter Amplitude . . . ±15dB

Peak Filter Freq. Range . . . . . 20Hz-20KHzPeak Filter Bandwidth . . . . . . 3 1/3 to 1/20 OctavePeak Filter Amplitude . . . . . . ±15dB

Max. Level - All Filters In,All Level Controls at Unity . . +23dBu

Max Level - One Peak Filter at Max Boost"Q" 0.3 octave or greater . . . +7dBu

Output Connections . . . . . . . . 1/4" Phone Jack, XLR 200Ω Pseudo-Balanced* 100Ω Unbalanced

Max Output Level . . . . . . . . . . +23dBu

Frequency Response . . . . . . . . ±.2dB 20Hz-20kHz

THD (20Hz-20KHz) . . . . . . . . <.03%@+4dBu

Output Noise20Hz-20KHz unweightedAll controls at unity gainEQ Out . . . . . . . . . . . . . . . . . . <-109dBuEQ Peak Filters In . . . . . . . . . <-93dBuEQ Peak and ShelvingFilters In . . . . . . . . . . . . . . . . . <-90dBu

(0dBu = 0.775 volts rms, balanced input)

*Pseudo-balanced output is single ended signal with bal-anced impedance.

16


14. DIMENSIONS

B

B

B

B

B

B

B

SPECIFICATIONS (continued): Compressor/Limiter

Gain: . . . . . . . . . . . . . . . . . . ±15dBRatio: . . . . . . . . . . . . . . . . . . 2:1 → ∞Attack Time: . . . . . . . . . . . . 200µS-20mSRelease Time: . . . . . . . . . . . 100mS-3SecOutput: . . . . . . . . . . . . . . . . . . -∞ to +18dBMaximum Input Level: . . . . +23dBuMaximum Output Level: . . +23dBuInput Impedance: . . . . . . . . 20KΩ balancedOutput Impedance: . . . . . . . 200Ω Pseudo-Balanced

Frequency Response: . . . . . ±0.2dB 20Hz-20KHzDistortion: . . . . . . . . . . . . . . <.01% THD, 0dBu, 1KHz

<0.15% THD, +15dBu,20Hz-20KHz

Output Hum and Noise: . . . <-95dBu

DPX-100 Power Requirements:93VAC-120VAC, 50-60Hz, 10W

Size and Shipping Weight:19"L x 1.75"H x 6"D (8 lbs.)

17

Operating M

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X-200 Param

etric Equalizer - C

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15. SCHEMATICS

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C3847u

56 4

SW10BSW-DPDT

D91N4148

C39

47uR7310K

R7410K

F2 IN F3 INF1 IN F4 IN

PEAK BUS 2

F4 OUTF2 OUT F3 OUTF1 OUT

OUTOUTOUTOUT

1.6KHz - 16KHz20Hz - 20KHz 20Hz - 20KHz40Hz - 400Hz

+/- 15 dB to each filter

LEVEL

C44

68p

D60

1N4148PEAK BUS 2

23

1 SW13A

45P2600

56

4SW13B

45P2600

R48160

R49

620

R50

620C32.001u

C45.001u C46

100p

C61100p

R513.3K

C87

47u 63v

C88

47u 63v

R52

10

R117

10

+18

-18

R1188.66K

R1198.66K

2

31

Q42N4125

2

31 Q5

2N4125

C62220p

C70.0022u

R1205.90K

VR8B10C2K

C89

3300u 6.3v

R121

10

R1225.90K

R1232.55K

R1242.55K

C72

220p

3

21

U7A

4560

R1258.66K

R126

8.66K

C73

100p

C74

100p

C90

47u

C91

47u

R127

15K

R128

2K

R129

18K

C75

27p

C92

47u

23

1 SW14A

SW-DPDT

J5

47P3151

13

2J7

47P1030

R44100

R45100

C7147U

R4610K

OUTPUT

5

67

U6B

4560

R176 10K

R177

10K

J1

47P3151

J2

47P3151

13

2J6

47P1030

13

2J8

47P1295

3

21

U1A

4560 5

67

U2B

4560

R1100

R2

100

R3

10.0K

R4 10.0K

R510.0K

C127P

C2

27P

C64

47UR6 10.0K

VR1B10K

R7

22K

R84.7K

R9

22K

C3 27P

R10

15K

D11N4148

R1168

R124.7K

R1368

R14

300K

VR750K

Ec+

2

1 8

V-

5V

+7

Ec+

4

GN

D6

Ec-

3

U18

52P2150

-18

+18

+18

-18

3

21

U2A

4560

R15 15K

C4 27P

C65

47U

J3

47P3151

R161K

5

67

U1B

4560

5

67

U3B4560

VR2B100K

C66

47U

R179.76K

R181M

R19100K

R20100K

C5

5pF

C67 47U

R21

10KR22 4.99K

R23

3.3K

R24

47K

R25

150K

R2610K

R27

10K

3

21

U3A4560

D21N4148

D31N4148

D41N4148

5

67

U4B

4560

D15

1N754

D5

1N4148

23

1SW1A

45P2600-18

2

31

Q12N4125

R28100

VR3A10K

3

21

U4A

4560

-18

VR4A1MEG

R29

100K

C79

1.5U

C80

1.5U

R3068K

R313.3K

Q62N4123

+18

R321K

R331K

VR5C10K

C6847U

R3410K

5

67

U5B

4560

VR6B10K

R35

10K

R36

820 R37 12K

C6

27P

C69

47UR3810K

D6

1N4148

OUTPUT METER

PEAK BUS 1

INPUT METER

PEAK BUS 1

GAIN METER

THRES

OUTPUT

BALANCEDINPUT

GAIN +/- 15dB

DETECTORTIP = INPUTRING = SEND

SYMMETRY ADJUST

THRESHOLD(-20db MIN +41.4dB MAX)

OUTPUT(+17.0dB MAX)

LIMIT

OUT

RATIO

ATTACK

RELEASE

23

1SW5A

45P2000

CHAIN

IN

56

4SW5B

45P2000IN

D531N4148

PEAK BUS 1

HS IN

F2 INF1 IN

LS IN

HS OUT

LS OUT

F1 OUTF2 OUT

FILTERS10s5751c-2.SCH

PEAK BUS 1PEAK BUS 2THRES

GAIN METER

INPUT METEROUTPUT METER

PWR SUPPLY + METERS10s5751c-3.SCH

REVISION HISTORY10s5751RV.SCH

13

2J20

47P1295

D71N4148

D611N4148

D621N4148

D631N4148

R1306.8K

R1316.8K

+48

R13410K

R13510K

GAIN +20 to +55dB

GAIN +15db MAX

-20dB PAD

OUT

OUT

18 Operating M

anual - DP

X-200 Param

etric Equalizer - C

ompressor/L

imiter

1 2 3 4 5 6 7 8

A

B

C

D

E

87654321

E

D

C

B

A

B

APPROVED: Dwg #

Size Drawn By Rev.

CS:\Engineering\CLIENT98\5751\10s5751c-2.SCH

10S5751


James B FranksSheet # of2 4


Phone: Fax:(716) 872-0010 (716) 872-0739

Print Date

10-Sep-2002

14:27:46A->B @ 157%

C $VKO\ $XGLR ,QF

5

67

U10B

45605

67

U7B

4560 3

21

U15A

45605

67

U15B

4560

3

21

U11A

45605

67

U12B

4560

5

67

U11B

4560

R75

4.7K

R7610K

R77

3.3K

R782.7K

R7910K

R806.8K R81

10K

R8210K

R83

680

R841.5K

R85

1.15K

R8610K

R8722K

R88

10K

R89

8.2K

R9047K

R91

3.3K

R921K

R93

33K

R94

1M

R95

10K

R96

10M

C40

47u

C41

47u

C42

47u

C12

.068u

C13.22u

C14

.0015u

C15

27P

C16

.0015uC17

.0068u

C18

.0015u

VR11BC100K

VR11AC100K

VR12BC100K

VR12AC100K

56

4 SW11B

45P2600

3

21

U12A

4560R97

1.15K

R98

10M

C19

.068u

C20

.0015uC21

.0068u

C22

.0015u

23

1 SW11A

45P2600

VR13AC100K

VR13BC100K

VR13CB10K

Frequency

Range

OUT OUT

3

21

U13A

45605

67

U14B

4560

5

67

U13B

4560

R996.8K R100

10K

R10110K

R102

680

R1031.5K

R104

1.15K

R10510K

R10622K

R107

10K

R108

8.2K

R1091K

R110

33K

R111

1M

R112

10K

R113

10M

C43

47u

C23

.068u

C24

27P

C25

.0015uC26

.0068u

C27

.0015u

56

4 SW12B

45P2600

3

21

U14A

4560R114

1.15K

R115

10M

C28

.068u

C29

.0015uC30

.0068u

C31

.0015u

23

1 SW12A

45P2600

VR14AC100K

VR14BC100K

VR14CB10K

Frequency

Range

OUT OUT

F1 INF1 OUT F4 IN

F4 OUT

F3 IN

F3 OUTF2 OUT

F2 IN

Low Shelf High Shelf

Filter ThreeFilter Two

D581N4148

Peak Bus 2

D591N4148

Peak Bus 2

BandwidthBandwidth

Filter One Filter Four

19

Operating M

anual - DP

X-200 Param

etric Equalizer - C

ompressor/L

imiter

1 2 3 4 5 6 7 8

A

B

C

D

E

87654321

E

D

C

B

A

B

APPROVED: Dwg #

Size Drawn By Rev.

CS:\Engineering\CLIENT98\5751\10s5751c-3.SCH

10S5751


James B FranksSheet # of3 4


Phone: Fax:(716) 872-0010 (716) 872-0739

Print Date

10-Sep-2002

14:27:05A->B @ 157%

C $VKO\ $XGLR ,QFPEAK BUS 1

PEAK BUS 2

THRES

SIG

GAIN METER

INPUT METER

OUTPUT METER

14

5

63 2

out

SW6

45P1501

14 5 6

3

2

out

SW7

45P1501

LGN

J10

47P1413

D19

1N4003

D20

1N4003

D21

1N4003

D22

1N4003

C851000u

C861000u

In1

2

Out 3

U197818

In2

1

Out 3

U207918

D231N4003

C811.5u

C821.5u D24

1N4003

D251N4003

-18C47.1U 100V

C48.1U

C49.1U

R1441.5K

+18

J11KEYSTONE

F1

1/2 AGC

110VAC 220VAC

2 11

3 104

58

T1

51P7308

R14510K

R1463.3K

D161N754

D101N270

C50

220P

2

31

Q22N4125

C51

.1U

+18

+18-2

VCC + FOR IC 5

R1471.5K

56 4

SW1B45P2600

D26LIMITER(G)

D27POWER(Y)

+18

OUT

Q72N4123

Q82N4123

R148

390K

R149

2.4K

R15062K

C52.1U

D28+20(R)

R1511.5K

PEAK BUS 1

SIG

IN5

MO

DE

9

RL

O4

RH

I6

RE

F A

DJ

8

V+

3V

-2

RE

F O

UT

7

LE

D10

10L

ED

911

LE

D8

12L

ED

713

LE

D6

14L

ED

515

LE

D4

16L

ED

317

LE

D2

18L

ED

11

LM

3915

U21LM3915

D29

+6(Y)

D30

+3(Y)

D31

0(Y)

D32

-3(G)

D33

-6(G)

D34

-9(G)

D35

-12(G)

D36

-15(G)

D37

-18(G)

D38

-21(G)

+18

J13/2A

J13/2B

J13/2C

J13/2D

J13/2F

J13/2G

J13/2E

J13/2H

J13A

J13B

J13C

J13D

J13F

J13G

J13E

J13H

23

1

SW4A

45P2600

INPUT METER

OUTPUT METER

-18

+18 +18

-18

R1524.7K

D171N964

-18

+18

R153

2.4K

R154

2.4K

3

21

84

U5A

4560

D11

1N4148

D121N4148

R155

1K

R156

100K

R157

100K

C831.5U

OUT

METER SELECT

OUTPUT LEVEL (db)

2

31

Q32N4125

Q92N4123

R158

560

R15915K

R160100K

R1611.5K

D131N4148

D141N4148C841.5U

C7647U

D39

(Y)

+18

THRES

SIG

IN5

MO

DE

9

RL

O4

RH

I6

RE

F A

DJ

8

V+

3V

-2

RE

F O

UT

7

LE

D10

10L

ED

911

LE

D8

12L

ED

713

LE

D6

14L

ED

515

LE

D4

16L

ED

317

LE

D2

18L

ED

11

LM

3914

U22LM3914

D40

-20(R)

D41

-18(R)

D42

-16(R)

D43

-14(R)

D44

-12(R)

D45

-10(R)

D46

-8(R)

D47

-6(R)

D48

-4(R)

D49

-2(R)

+18

J14A

J14B

J14C

J14D

J14F

J14G

J14E

J14H

J14/2A

J14/2B

J14/2C

J14/2D

J14/2F

J14/2G

J14/2E

J14/2H

GAIN METER

-18-18

-18 -18

+18+18

+18

R1624.7K

D181N964

-18

R163

4.7K

R164

2K13V

GAIN REDUCTION (db)

C53.1U

C54.1U

C55.1U

C56.1U

C57.1U

C58.1U

C59.1U

C60.1U

Q102N4123

Q112N4123

D50CLIP(R)

R1651.5K

R16662K

R167

390K

R168

2.4K

+18

C63.1U

PEAK BUS 2

J12KEYSTONE

J15KEYSTONE

COMPRESSOR/LIMITER METERS

EQ METER & LIGHTS

+19 dBu

D52

1N4003

J16KEYSTONE

J17KEYSTONE

J18KEYSTONE

J19KEYSTONE

-18

+18-2

J21KEYSTONE

23

1 SW9A

45P26002

3

1 SW8A

45P26002

3

1 SW3A

45P26002

3

1 SW2A

45P2600

D51

F3(G)

D54

F4(G)

D55

F2(G)

D56

F1(G)

OUT

R116

1.5K

+18

23

1 SW10A

45P2600

D57

EQ(G)

D64

1N4003

D65

1N4003

D66

1N4003

C77

100u 100v

C78100u 100v

C93100u 100v

+48

56 4

SW16B45P2600

R1381.5K

23 1

SW16A45P2600

D68Phantom (R)

-18

OUT

ADJ1 IN3 OUT 2U16

LM317T

D67

1N4003

R132243 1%

R1339.09K C94

NONE

C951.5u

R43

470

Printed in USA 0902 DPX200 -0


ASHLY AUDIO INC. 847 Holt Road Webster, NY 14580-9103Phone: (585) 872-0010 Fax: (585) 872-0739

Toll Free (800) 828-6308 Internet: www.ashly.com 2002 by Ashly Audio Corporation. All rights reserved worldwide.

Documents

Parametric Equalizer Compressor/Limiter · DPX-200 Parametric Equalizer Compressor/Limiter Operating Manual ASHLY AUDIO INC. 847 Holt Road Webster, NY 14580-9103 Phone: (585) 872-0010