Transcript Fundamentals of Audio Production Chapter Nine: Audio Processors and Processing Fundamentals of Audio Production Chapter 9

Fundamentals of Audio
Production
Chapter Nine:
Audio Processors and Processing
Fundamentals of Audio Production
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Types of processing
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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
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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
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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 electromechanical
• 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 time
Click 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 hardsurfaced room was captured by a
microphone and returned to console for
blending with the “dry” sound
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Acoustic reverberation
Reflected
sound
Loudspeaker
Microphone
Reflected
sound
Dry
signal
Console
Effected
signal
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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
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