Effects
Effects
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Dynamic Range Processors
Fixed Time Delay Effects
Variable Time Delay Effects
Reverberation Effects
Time and Pitch Changing Effects
Distortion Effects
Dynamic Range Processors
• Affect the amplitude of signals
• Altering the amplitude affects the dynamic
range
• Dynamic range is the ratio of the loudest
possible (undistorted) signal to the quietest
(limited by noise)
Compressors
• An amplifier whose gain is controlled by
the amplitude of its input signal
• Best explained by using transfer functions
Transfer Functions
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Output
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Input
Inputs come in from base and are reflected by the solid
diagonal line to emerge on the right.
T. Func. For Compression
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Output
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Input
Extreme values at input map to less extreme values at
output.
The Effect of Compression
Effect of Compression Cont...
• Reduces peaks in a signal allowing the
overall amplitude to be raised without
distortion
• So increases perceived loudness
• Focuses sound: making foreground parts
louder and leaving background parts alone
Use of Compression
• Often used on vocals and drums
• Overuse can make treble sounds grate the
ear
• Extreme compression can be used to create
distortion
Compression Parameters
• Threshold – the level in dB above which the
signal is attenuated
• Ratio – governs the amount by which the
signal is reduced
Compression Ratio
• A ratio of 4:1 would reduce the amplitude
of a signal 4dB above the threshold so that
it was only 1dB over the threshold.
Other Compression Parameters
• Attack - controls how quickly the compressor
starts to act (can preserve timbre)
• Release - controls how quickly the
compressor stops acting
• Knee - compresses as signal approaches
threshold to avoid sudden changes
Expanders
• Are similar to compressors but they raise
rather than lower amplitude of signal when
it exceeds threshold
• They enliven an audio signal
• Rarely used
Expansion
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Output
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Input
The Effect of Expansion
Limiters
• Used to prevent clipping
• Whilst preserving maximum overall level of
the signal
• Prevent the destruction of speakers in live
situations
Limitation
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Output
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Input
The Effect of Limitation
Other Dynamic Range Processors
• Envelope Shapers
• Noise Gates
• De-Essers
Fixed Time Delay
• Most delays enable the user to feed a
percentage of the delayed signal back into
the input
• This creates an echo
The Use of Delay
• Longer delays (over 50ms) create echoes
• Shorter Delays (under 10ms) alter the tonal
quality of a sound (thicken/thin)
• Medium Delays (10 - 50ms) can enhance a
thin signal
• Delays can also be used to enhance the
stereo position of tracks in the mix
Delay Line Implementation
• Delay effects often use a circular queue
• Queue of 8 samples contains the last 8
samples played
A Two Tap Delay Line
sample
played
“O” marks position of
oldest sample.
sample
played
“N” newest sample.
The taps are where
samples are read and
played.
incoming (new)
sample
Delay Parameters
• Dry - percentage of original signal played
• Wet - percentage of delay signal played
• Feedback - how much of wet signal gets fed
back into the queue
Reverb
Sound bouncing off walls, ceilings etc.
Reverb Reflections
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Are of lower amplitude
Slightly delayed
Effectively low pass filtered
Concert hall has an echo density of 1000
reflections per second
Artificial Reverb
• Produced in various ways:
• Spring Reverb - sound after it has been passed
through a spring
• Plate Reverb - sound recorded through sheet
metal
• Chamber/Hall reverb - put a speaker in a
bathroom and record
Implementation of Reverb
• Most reverbs used today are digital
algorithms
• Use comb and all pass filters, with a multi
tap delay line for early reflections
• Reverb can also be simulated by convolving
the input signal with the impulse response
signal of a room
Reverb
initial
impulse
early
reflections
amp.
fused
reverberations
pre-delay
reverb
decay time
time
Reverb Parameters
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Type - changes reverb algorithm
Colour - alters the character of the effect
Size - changes the size of the room
Pre-delay - time before reverb starts
Reverb Parameters Cont...
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Decay - time before reverb fades away
Mix - dry(original) / wet (effected) sound
Diffusion - echo density
Input Delay - causes wet to precede dry
sound
Reverb in Logic
• EnVerb - manipulation of amplitude
envelope of reverb tail
• PlatinumVerb - early reflection editing
• Space Designer - convolution reverb
Convolution Reverb
• Impulse containing all frequencies is played
in a space (e.g. a church)
• Impulse response (IR) is the sound that
comes back
• Convolution reverb convolves a sound
signal with an IR
• Result: the sound signal in the space the IR
relates to
Variable-Time Delay
• Chorus
• Flanging
• Phasing
Chorus Effects
• Produce the subtle pitch and timing
differences that occur when several people
perform together
• For example, by using a multi-tap delay line
and varying the delay times over a narrow
range using LFOs
Flangers
• Produce spacey/underwater effects
• For example, by delaying the original signal
and slowly varying delay time between a
few milliseconds and zero
Phasing
• Produces a ‘soaring’ sound
• Originally two tapes of the same thing
slightly out of time
• Implemented using all pass filters (to alter
the phase of the signal) and LFOs (to alter
phase shift)
Time & Pitch Effects
• Allow the time or pitch of a signal to be
altered independently
• E.g. by using a granular synthesis, here
• time stretching means repeating grains
• increasing pitch means playing back grains
at increased speed and repeating grains
• decreasing pitch means reducing the speed
of playback and skipping grains
Distortion Effects
• Simulate the distortion produced by:
• digital circuits
• analogue devices (e.g. vacuum tubes)
Logic’s Analogue Distortion
• FX include:
 Overdrive - simulates the distortion
produced by a field effect transistor
 Clip Distortion - simulates warm, overdriven
tube amp sounds