Effects

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 Input Output Inputs come in from base and are reflected by the solid diagonal line to emerge on the right.

T. Func. For Compression Input Output 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 Input Output

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 Input Output

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 ( ms) 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 “O” marks position of oldest sample. “N” newest sample. The taps are where samples are read and played. sample played incoming (new) sample sample played

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 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 early reflections initial impulse amp. reverb decay time pre-delay fused reverberations time

Reverb Parameters 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... 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