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MetropolitanCommunityCollegeAudio Video Production
EngineeringPart 1 Audio
Rev. 6.4fThis PowerPoint and other resources may be found at:http://faculty.mccneb.edu/ccarlson/vaca1010.htm
Nature of Sound Waves
Sounds in air are commonly produced Vocal cords, Speakers, Instruments, etc.
2
Air particles
As the sound source pushes against air particles they are compressed.
As the sound source moves away they are rarefied.
3
4
Loudness VS Distance
Loudness follows an Inverse-Square Law
Intensity of sound is inversely proportional to the square of the distance from the source.
5
Sound and Hearing
The Human EarOuter EarMiddle EarInner Ear
6
Courtesy of Dr. John S. OghalaiUsed by permission
PinnaLabyrinth
7
Courtesy of Dr. John S. OghalaiUsed by permission
8
Frequency and Sound
20 Hz
60 Hz
120 Hz
240 Hz
480 Hz
960 Hz
1920 Hz
3840 Hz
7680 Hz
15360 Hz9
0
1
2
3
4
5
67
8
1
2
3
0
5
6
8
0 45 90 135 180 225 270 315 360
Time
Time
Rotation in Degrees
The number of rotations per second is equivalent to the frequency
1/T = F 1/F = T 1/1000 = .001 1/.001 = 1000
Distance = Velocity X Time
Velocity of sound in air = 331.3 + 0.6Tc (m/s)@ 75 degrees = 245.97 M/S or 1135.08 F/S or 774.98 M/Hr
1135.8 X .001 sec. = 1.1358 Ft. (1 KHz)1135.8 X .05 sec = 56.79 Ft. (20 Hz)1135.8 X .00005 sec = .05679 Ft. (.68148 In.) (20 KHz)
The Sine Wave
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4
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Wavelength & Frequency
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Amplitude & Phase
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1
2
3
0
5
6
8
7
4
1
2
3
0
5
6
8
7
4
90 degrees out of phase
180 degrees out of phase
1
2
3
0
5
6
8
7
4
In phase
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Decibel
Unit of measure BelBased on ratioUsed for both Acoustic and
electrical applications
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dB formulas
PowerdB = 10 log (P1/P0)Voltage and AcousticdB = 20 log (E1/E0)
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dB as Unit of Measure
Requires a reference3 and 10 rule (power)6 and 20 rule
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3 & 10 and 6 & 20 Rule
Power 3 dBW 10 dBW
Other 6 dB 20 dB
Multiplier + X 2 X 10
Multiplier - ÷ 2 ÷ 10
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Add and Subtract dB
dB change Total Result
+6 dB 6 dB X 2
+6 dB 12 dB X 4
+20 dB 32 dB x40
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dB Standards
0 dBW = 1W100W amplifier is 20dBW1000W amplifier is 30dBW
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dB Standards
0 dBm = 1mw>600 Ohm load (.775 V)
0 dBu = .775 V0 dBv = .775 V0 dBV = 1 V
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Click chart for sound21
SPL Meter
Microphone Amplifier MeterA Weighting filter inverse of
equal loudness contoursB & C Weighting high end of
equal loudness contours
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Weighting Networks
A weighting 10 – 55 dBB weighting 55 – 85 dBC weighting 85 – 140 dB
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Weighting Chart
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Loudness of sound (dB)
Threshold of hearing 0Normal conversation 60City traffic inside car 85Sustained exposure results in
hearing loss 85-90Power Mower 107
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Loudness of sound (dB)
Rock concert front row 115Pain begins 120Jet engine @ 100’ 140Death of hearing tissue 180Loudest sound possible 194
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dB Meter
Specialized AC Meter with scale calibrated in dB
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VU Meter
Much the same as dB meterCalibrated 0VU = __dBResponse peak to averageAnalog, LED, Electronic
display
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Noise InducedHearing Loss
Base level 85 dB for 8 hrsEach 3 db increase 1/2 time“A” weighting measurementMost sensitive at 4 KHz40 yrs @ 85dB = NIHL 8%
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End Week 1
Review Week 2
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Magnetic Polarity
Like Poles RepelUnlike Poles Attract
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0- +
MagneticField
Directionof Travel
0- +
MagneticField
Directionof Travel
0- +Magnetic
Field
Directionof Travel
.
+
N S
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Electromagnetic InterferenceA Moving magnetic field
across a stationary conductor has same effect as a moving conductor in a stationary magnetic field
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Magnetic field is generated around wires carrying current
Magnetic polarity changes as direction of current flow changes
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Capacitors
Two metallic platesInsulated from each other(insulation called dielectric)
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Capacitors store electronsCapacitors behave much
like a water towerFilling the water tower is
like charging a capacitorUsing the water is like
discharging a capacitor39
Unit of Measure
The Farad is the unit of measure. Typical values are Micro Farad or Pico Farad. Larger values store more electrons.
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Capacitor Behavior
Capacitors block DC current and pass AC current
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Capacitor Behavior
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Dynamic CapacitorMicrophone Microphone
N
S
Output Diaphragm
Moving coilattached toDiaphragm
Diaphragm(front plate)
Spacer
Back plate(fixed)
Output
Ribbon Microphone
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A microphone sensitivity specification tells how much electrical output (in thousandths of a volt or "millivolts") a microphone produces for a certain sound pressure input in dB SPL (usually 94dB SPL)
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If two microphones are subjected to the same sound pressure level and one puts out a stronger signal (higher voltage), that microphone is said to have higher sensitivity.
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Microphone Pickup PatternsOmni-directional: picks up
sound from all directionsDirectional: picks up sound
from one directionBi-directional: picks up
sound from two directions46
Pick-up Patterns
47
Polar Pattern
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Directional Microphones
Directional Microphones called Cardioid, Supercardioid, Hypercardioid
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Directional Microphones
Proximity effectDo not “reach” furtherGenerally do not have as
smooth of a response curve as Omni-directional
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Phantom Power
2
31
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Muting Capacitor Mics
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Muting Capacitor Mics
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The 3 to 1 rule
The distance between microphones should be at least 3 times the distance from each microphone to its intended sound source.
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Comb Filtering
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Connecting to Cameras
Front input and Back inputSelect Mic. or LineIf Mic., Phantom on or offSelect Auto or Manual levelsAssign which is Ch.1 or Ch.2
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How Speakers Work
http://electronics.howstuffworks.com/speaker5.htm
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Block Diagrams
Used to make complex circuits or systems easy for the user to comprehend and use
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Block Diagrams
Most common symbol is a square or rectangle
Triangles often usedInterconnected by lines
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Block Diagrams
Direction of lines importantINPUTS – top and leftOUTPUTS - bottom and
rightUse arrows when not
standard60
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Blue lines SDIBlack lines Composite
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Amplifiers
Electronic devices used to increase an electronic signal level
Many types and kinds
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Amplifier CharacteristicsGainImpedance input/outputBalanced input/outputUnbalanced input/output
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Audio Amplifier Types
Pre amplifierBuffer amplifierLine amplifier/DAPower amplifier
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Pre Amplifier
Frequently used in low level applications
Phonograph cartridgeMicrophoneIntercom
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Buffer
Often used to isolate one circuit from another and to match impedances
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Line Amplifier/DA
Often used to increase drive capability
Split signals to feed several different pieces of equipt.
Usually no change in level
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Power Amplifiers
Usually used to increase current capability to drive speakers and headphones
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Combining Speakers
Speakers connected in Series, Z adds directly
Speakers connected in Parallel, If Z is all the same value, Total Z = Z/Number of spkrs.
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Combining Speakers
If Z has different values calculate using:
1 Z total = 1 + 1 + 1 Z1 Z2 Z3
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Distributed Sound
Add All tap values in system. Amp power used should be 80% of amp rating
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End Week 2
Review Week 3
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Ohm’s Law
E=IRE is voltage in voltsI is current in ampsR is resistance in Ohms
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Rearranging Formula
E=IRI=E/RR=E/I
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Power Law (Watt’s Law)
P=IEP is power in wattsI is current in ampsE is voltage in volts
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Rearranging Formula
P=IE P=I2R P=E2/RI=P/EE=P/I
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Electrical Circuit Rating
Most modern circuits for outlets are 120 V 20 A
2400 watts are available per circuit
Codes vary for how many outlets can be on a circuit
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Impedance
The total opposition to an alternating current and is measured in Ohms
Symbol for impedance is Z
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Complex calculations
Impedance = square root of reactance squared + resistance squared.
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Reactance & Frequency
Capacitive ReactanceXc=1/2∏fC
Inductive ReactanceXl=2∏fL
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Wiring Characteristics
Impedance and ResistanceImpedance for AC circuitsResistance for DC circuitsBoth measured in Ohms
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Measurement
Resistance measured directly with meter
Impedance calculated or measured with bridge
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Bridge Measurement
Meter
0- +
UnknownReference
Reference Adjustment
AC signal
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Cable Characteristics
Conductor size (AWG)Number of ConductorsTwist or no twistShieldingInsulation type
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AWG
24-26 Guage used for Phone & Computer wiring
22 Guage often used for Audio Mic. & Line level
16-18 Guage 70V Speaker distribution
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AWG
18-10 Guage used for 2 Ω -16 Ω speakers
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Number of Conductors
Unbalanced audio 1 conductor plus shield or ground connection.
2 conductors needed to complete circuit
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Number of Conductors
Balanced audio 2 conductors, may also have a shield but not required
Speaker 2 conductors with no shield
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Twist or No Twist
Twisted pairs used with low level audio and many other services (data, phone, etc.)
No twist mainly for power
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Shielding
Shield must be connected on both ends for Phantom powering of microphones
Connecting shields on one end may be good for hum, but increases RFI chances
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Phantom Power
2
31
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Insulation Type
Plenum and non-plenumPortable and Installed wireRoHS compliant
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RoHS Compliant
The RoHS directive aims to restrict certain dangerous substances commonly used in electronic and electronic equipment
(Restriction of Use of Hazardous Substances)
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RoHS Compliant
. Any RoHS compliant component is tested for the presence of Lead (Pb), Cadmium (Cd), Mercury (Hg), Hexavalent chromium (Hex-Cr),
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RoHS Compliant
Polybrominated biphenyls (PBB), and Polybrominated diphenyl ethers (PBDE). Some military and medical equipment are exempt from RoHS compliance.
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Common Connectors
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Speaker Wiring
Maximum loss of 5% of nominal speaker impedance.
Example 8 Ω speaker, 5% = .4 Ω.
22 gauge wire has resistance of 0.0164 Ω per foot
1 wire each way (2 wires) = 0.0328 Ω / Ft.
.4/.0328=12.195 or 12' for 5 % loss.
Speaker Wire Chart
Copper Wire Size
2 Ohm
4 Ohm
6 Ohm
8 Ohm
22 3 6 9 12
20 5 10 15 20
18 8 15 23 30
16 12 25 37 50
14 20 40 58 77
12 31 61 92 123
10 50 98 147 196
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Wire Calculator
http://circuitcalculator.com/wordpress/2007/09/20/wire-parameter-calculator/http://en.wikipedia.org/wiki/American_wire_gauge
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Balanced Wiring
+
- Input
OutputX
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Common Mode Rejection
+
-Common Mode OutputX
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Unbalanced Wiring
+ Input
Output
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Audio Class of Service
Microphone level (-50 dB)Line level (0 dB)Speaker levelVideo (1V Noisy)RF (Saturates Amplifiers)Data (HF Noisy)
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End Week 3
Review Week 4
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Equipment InterconnectPower GroundingEarth/ChassisSignal Grounding
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Ground Loops
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Transformers
Turns RatioStep-up/Step-downImpedanceOther PropertiesSee also
http://www.energyquest.ca.gov/how_it_works/transformer.html
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Transformers
Isolation Step-down Step-up
Polarity
+
+
Polarity
+ +
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Transformer Isolation
Courtesy Rane Corporation (RaneNote 110)Used by permission
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Power For Equipment
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Two Bus for 220V
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Patch Panels
1 24
25 48
From Equipment (Outputs)
To Equipment (Inputs)
Normalling Jack Pair
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The right way to do it.
Courtesy Rane Corporation (RaneNote 110)Used by permission
115
Courtesy Rane Corporation (RaneNote 110)Used by permission
116
See AlsoEPM Mixerguide pg 30
(A) Off the Shelf cable(B) 6dB sig.loss
Courtesy Rane Corporation (RaneNote 110)Used by permission
117
Courtesy Rane Corporation (RaneNote 110)Used by permission
118
Courtesy Rane Corporation (RaneNote 110)Used by permission
119
Shortcuts+ Tip
+ Pin Shield Shield (Sleeve)
+ Tip
- Ring
- Pin 3
+ Pin 2
Shield Pin 1
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Balanced to Unbalanced
- Pin 3 N/C
+ Pin 2
Shield Pin 1
Shield
+ Pin 2
- Pin 3
Shield Pin 1 Jumper
BalancedOutput
BalancedInput
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Soldering Connectors
See “A guide to soldering” and “EPE basic soldering guide” on my Website
122
Soldering Video
RCA connectors¼” connectorsXLR connectors
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Equalization
Very complex topic1. Sound reinforcement2. Vocal3. Instruments
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Sound Reinforcement
There is no one correct way to equalize a sound system. Type of system and size of the space has a giant impact EQ technique.
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Distributed Sound
Using Parametric EQ, try to adjust the system EQ using pink noise and spectrum analyzer for near flat response (slight HF roll off OK)
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System EQ
Once System EQ is adjusted, individual vocal channels or instrument channels may be adjusted for “BEST MIX”
127
Basic Terms
OctaveAn octave is the interval
between two points where the frequency at the second point is twice the frequency of the first.
128
Frequency & Octaves
63 Hz 1 125 Hz 2250 Hz 3 500 Hz 41 KHz 5 2 KHz 64 KHz 7 8 KHz 816 KHz 9
129
“Q” rating
The "Q" control sets the width of the band of frequencies that will be boosted or reduced
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“Q” Chart
Q Setting Bandwidth 0.7 2 Octaves 1.0 1 1/3 Octaves 1.4 1 Octave 2.8 1/2 Octave
131
Equalizer Types
Graphic equalizer, Several varieties
Shelving (highpass-lowpass) High or low cut or boost
Parametric, Boost, cut, center freq & Q
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Speech Characteristics
Cover three main frequency bands
FundamentalsVowelsConsonants
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Fundamentals
125 – 250 HzEssential for voice quality(who is speaking)315 – 500 Hz also important
to voice quality
134
Vowels
Contain the maximum energy & Power of the voice 350 Hz – 2,000 Hz
630 – 1 KHz Important for natural sound
135
Consonants
1,500 – 4,000 Hz contain little energy but are essential to intelligibility
1.25 – 8 KHz governs the clarity of vocals
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Energy
63 – 500 Hz contain 60% power and 5% intelligibility
500 – 1 KHz contain 35% power and 35% intelligibility
1K – 8 KHz 5% power and 60% intelligibility
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EQ Problem…Vocals
Boost 100 – 250 BoomyCut 150 – 500 Boxy, HollowCut 500 – 1 KHz hardnessBoost 1 – 3 KHz metallicCut 2 – 5 KHz lifelessBoost 4 – 10 KHz gritty, sibilance
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General Tips
Be sure level is correct before EQ (don’t use EQ to make up for low level)
Boost less Cut moreDo not boost fundamentalsAvoid boosting the same
frequency for 2 instruments
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General Tips
Do not use EQ to make-up for poor microphone placement
Keep track of what works best for your mixes. Use notes as starting point to save time during sound check
140
Equalization Primer
Follow link for more information about equalization.
http://www.menet.umn.edu/~kgeisler/EQ/primer.htmhttp://tweakheadz.com/EQ_and_the_Limits_of_Audio.html
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End Week 4
Review Week 5
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Magnetic Tape
Back coatPlastic baseBinderMagnetic coating
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Magnetic Tape
Several different coatingsIron oxideChromium dioxideCobalt DopedMetal
145
Magnetic Tape PropertiesNot detailed in this classCoercivity, Retentivity,
Sensitivity, Print through, Dropout, and many more
146
Recording Process
Recording is non-linear at audio frequencies
Bias current is needed to make recording linear
Bias adjustment depends on type of tape
147
Bias
Frequency Around 100 KHzApplied to Erase HeadModulated by Audio
148
Head Gap
Direction ofTape Travel
Head CoreHead Coil
Track Width
149
Mix Bus
Common point where multiple signals are combined
Summing point
150
Attenuators
Used to reduce signal levelMany typesGain controls do not do the
same thing
151
Refer to EPM Mixer Guide
Functional descriptionBlock DiagramHow to use some functions
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155
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158
159
160
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162
163
164
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Audio Studio Photos
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Audio Studio Photos
167
Audio Studio Photos
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End Week 5
Review Week 6
169
Digital Audio
A to D ProcessStorageD to A Process
170
A to D Process
Sampling RateHow many times per
second is the analog signal looked at
CD is 44,100/Sec
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Sampling vs Frequency
Sampling rate needs to be twice the frequency of the highest audio frequency needed
172
Sample Rate
Analog Signal Sample Points
173
Anti-aliasing
A low pass filter us used to limit high frequencies prior to sampling
174
Number Systems
DecimalBinaryOthers; octal, Hexadecimal,
etc.
175
WeightingNumber System Symbols
Binary 1 0
Decimal 9 8 7 6 5 4 3 2 1 0
Hexadecimal F E D C B A 9 8 7 6 5 4 3 2 1 0
Decimal104 103 102 101 100
10,000 1,000 100 10 1
Binary27 26 25 24 23 22 21 20
128 64 32 16 8 4 2 1
176
16 bit Binary
1-1, 2-2, 3-4, 4-8, 5-16,6-32, 7-64, 8-128, 9-25610-512, 11-1024, 12-2048,13-4096, 14-8192,15-16384, 16-32768,17-65536
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Quantization
The Value of each sampleTwo 8 Bit words (16 bits)
yields 65,536 graduations (used for each CD channel)
179
0
255
255 128 01 2 4 8 16 32 64 1280 0 0 0 0 0 0 1
180
1 2 4 8 16 32 64 128
#132
Clock
Modulated
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The D to A Process
DemodulationError CorrectionD to A ConversionSample and HoldLow Pass Filter
182
Demodulation
Restores the recorded signal to original ones and zeros
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Error Correction
Compensates for errors introduced during the recording process
184
D to A Conversion
Electronic process that converts digital numbers (samples) into analog voltage (current)
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http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/dac.html#c3
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Sample and Hold
Circuits that remove “Switching Glitches” that appear after D to A processing
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Low Pass Filtering
A circuit that does the final smoothing of the analog signal and removes any high frequency noise
188
Sample Rate Demos
Sample rate demoAnne Murray“You Needed Me”
189
File Conversion
http://www.nch.com.au/index.htmlFree tools for both Mac & PCAdvanced tools for purchase
190
File formats http://www.nch.com.au/switch/kb/1405.htmlwww.nch.com.au/acm/formats.html
191
File format conv. from.aac .3gp .aif/aiff/aifc.amr .ape .au .asf.avi .caf* .cda* .dct.ds2 .dss* .dvf* .flac.flv .gsm .m3u* .m4a*not supported on Mac
192
File format conv. from.m4r* .mid* .mod .moh.mov .mp2* .mp3 .mpc.mpga*.mpg .msv* .ogg.pls* .ra* .raw .shn.spx* .sri* .voc .vox.wav .wma .wmv .wv
193
File format conv. to.aac .aif/aiff/aifc .amr.ape* .au .caf* .flac.gsm.m3u .m4a .m4r*.mov# .mpe .mpc .ogg.pls .raw .spx* .vox.wav .wma* *not Mac #not Windows
194
Menu item options
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Menu item options
196
Wiring Considerations
Most digital connections use standard XLR connectors wired the same as balanced audio
Do not bundle/run with audio cabling
197
Wiring Considerations
Most MIDI hardware uses DIN-5 pin connections
Pins 4 & 5 carry digital signal Pin 2 is shield
50 ft maximum length
198
