fundamentals of audio production

Fundamentals of Audio Production Chapter 9

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Fundamentals of Audio Fundamentals of Audio ProductionProduction

Chapter Nine:Chapter Nine:

Audio Processors and ProcessingAudio Processors and Processing


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Types of processing

• Loudness processing

• Dynamic processing

• Frequency processing

• Temporal processing

• Digital processing

• Noise reduction processing


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Loudness processing

• Devices or circuits that add gain are “active” devices

• Most audio devices include a gain stage

• “Unity gain” means that the output level is equal to the input gain of the device or circuit


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Loudness processing

• Microphones have extremely low level outputs and require 40 decibels or more of amplification to be raised to “line level”

• Microphone pre-amplifiers raise the level to line level

• Power amplifiers then raise the level several more times to a level high enough to drive loudspeaker voice coils


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Loudness processing


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Loudness processing

• Decreasing gain is easily accomplished using attenuators – such as potentiometers

• Potentiometers are actually variable resistors

• Adding more resistance lowers the level or volume of the signal


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Potentiometers

As the wiper is moved further from the current input, the resistance is

increased and the volume level is decreased.


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Potentiometers

As the wiper is moved further from the current input, the resistance is

increased and the volume level is decreased.


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Potentiometers

Fade down – more resistance – less volume


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Pads• Pads are passive devices – requiring no power

and adding no gain• Pads provide gain reduction by adding

resistance• The amount of gain reduction is fixed• Rated in number of decibels of reduction


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Pads

Switchable -10 db pad on condenser

microphone


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Dynamic processors

• Limiters

• Compressors

• Noise gates

• All allow users to “automate” controlling levels


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Limiters

• Sometimes called “peak limiters”

• Allows user to set threshold and output level

• When signal exceeds the threshold level, the limiter decreases the signal – prohibiting it from exceeding the preset output level

• Often used in broadcasting


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Compressors

• In addition to adjustments for threshold and output-

• Also adjustments for ratio of reduction– Ratio of 2:1 provides 2 db of reduction for

every db over threshold– Ratio of 10:1 provides 10 db of reduction for

every db over threshold– Smaller ratios for more natural sound


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Compressors

• Also have user adjustable attack times– How quickly the gain reduction engages

• May also have adjustable release times– How long the signal reduction persists


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Noise gates

• Provide “all or nothing” signal passage

• Gate opens when the signal reaches the threshold level and allows signal to pass

• Gate closes when the signal falls below threshold and all signal flow stops

• In use: gated drum mikes will keep unwanted sounds from leaking in to recording


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Frequency processors

• Filters– Passive devices for cutting frequencies

• Equalizers– Active devices for boosting or cutting

frequencies


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Filters• Shelving filters cut a large band of frequencies• High pass, low pass and band pass


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Filters• Notch filters remove a narrow band of frequencies• Comb filters remove several narrow bands


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Equalizers

• Shelving equalizers boost or cut a wide band of frequencies


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Equalizers• Sweep equalizers boost a range frequencies by a

set amount of gain• The range of frequencies may be user-adjusted

or “swept”


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Equalizers

• Graphic equalizers provide a visual or “graphic” representation of the equalization curve

• Graphic equalizers are described by the interval between center frequencies of the user controls– e.g. full octave, one-half octave, one-third

octave


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Graphic equalizers


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Graphic equalizer


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Parametric equalizers

• Parametric equalizers allow the user to define – The frequencies that are being affected– The bandwidth of frequencies being affected,

called the “Q”– The amount of boost or cut being applied


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Parametric equalizers

• The controls on a parametric equalizer


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Parametric equalizer

Five band parametric equalizer


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Temporal processors

• Alter the “time” relationships of audio signals

• Simulate the effects resulting from the lapse of time when sound pressure waves travel through space

• Most common temporal effects are “delay,” “echo,” and “reverberation”

• Temporal effects help the listener aurally define the acoustic space


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Delay

• The time offset between a sound and the repeat of that sound

• In nature, a result of the reflection of the sound wave

• Early delay devices were electro-mechanical

• Signal was routed through an extensive electrical path which introduced time delay


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Delay

(effects send)

(effects return)


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Delay

Click on the speaker icon to hear a dry signal

Click on the speaker icon to hear an example of delay


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Echo

• An echo is generally defined as a single discrete reflection of a sound wave

• A result of the time that passes as the sound wave travels to a distant reflective surface and then back to the listener

• Echoes can be repeated – but will still be separate and distinct sounds if separated by enough timeClick the speaker icon to hear an example of echo


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Echo• Early echo devices used tape technology• The “Echoplex” employed a loop of tape and a

movable playback head to alter the period of delay between the live sound and the echo


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Reverberation

• A complex effect resulting from a series of reflections arriving at the listener’s ears separated by very short intervals

• The reflections appear to be a single sound that can be sustained over a long period of time

• Reverberation is added to recordings to simulate various acoustic environments


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Acoustic reverberation

• Reverb chambers used speakers and microphones to create and add reverberation

• Sound played from a speaker in a hard-surfaced room was captured by a microphone and returned to console for blending with the “dry” sound


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Acoustic reverberation

Dry signal

Loudspeaker Microphone

Effected signal

Reflected sound

Reflected sound

Console


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Electro - mechanical reverberation

• Spring reverberation – A spring suspended under tension is vibrated

by a transducer– Other transducers along the length of the

spring convert the vibrations back into sound that are delayed by varying times


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Spring reverberation


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Plate and foil reverberation

• Both plates and foil reverb devices are similar to springs

• Use transducers to convert sound into vibrations in metal plate or foil stretched under tension

• Other transducers convert the vibrations back into sound


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Electronic analog reverberation

• Analog delays used Bucket Brigade Delay (BBD) chips

• BBD chips named for their similarity to firemen bucket brigades – passing buckets of water from hand to hand

• BBD chips store electrical charges in a series of capacitors – charge is passed from “bucket to bucket”


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Electronic digital reverberation

• Digital signal processing (DSP)

• Audio is first converted in binary data

• Data is held in temporary memory locations in a delay circuit

• Data is then released and sent onward to a subsequent memory location

• The circuits through which the data is shifted are called “shift registers”


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Electronic digital reverberation

Click on the speaker icon to hear an example of reverberation


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Flanging and chorusing

• Effects created by very short time delays• “Flanging” named for practice of dragging

a finger on the flange of a tape reel• Flanging and chorusing are “phase shift”

effects• The signal is split and sent through a

circuit that introduces slight variable delay• Then signals are re-combined with slight

phase shifting


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Flanging and chorusing

Click on the speaker icon to hear an example of phasing

Click on the speaker icon to hear an example of flanging

Click on the speaker icon to hear an example of chorusing


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Harmonizers and pitch shifters

• Pitch shifters sample the frequency of the incoming signal, and then raise or lower the output frequency

• Harmonizers combine the shifted signal with the input signal to create multiple harmonies


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Noise reduction

• Noise reduction circuits were once merely shelving filters or band pass filters– Low pass filters would reduce tape hiss– High pass filters would reduce rumble

• Advanced digital noise reduction algorithms allow users to sample a sound, designate it as noise, and then eliminate it from the signal


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Forensic audio

• Forensic audio makes use of the various signal processors and algorithms to enhance audio recordings for investigative purposes

fundamentals of audio production

Documents

audio processors

recordingfundamentals

threshold level

volume level

db of reduction

gain stageunity gain

input gain

level high