#lang scribble/manual
@(require (for-label racket))

@title{(compander input control thresh slopeBelow slopeAbove clampTime relaxTime)}

Compressor, expander, limiter, gate, ducker.  General purpose
dynamics processor.

input: The signal to be compressed / expanded / gated.

control: The signal whose amplitude determines the gain applied to
         the input signal. Often the same as in (for standard
         gating or compression) but should be different for
         ducking.

thresh: Control signal amplitude threshold, which determines the
        break point between slopeBelow and slopeAbove. Usually
        0..1. The control signal amplitude is calculated using RMS.

slopeBelow: slope of the amplitude curve below the threshold. If
            this slope > 1.0, the amplitude will drop off more
            quickly the softer the control signal gets when the
            control signal is close to 0 amplitude, the output
            should be exactly zero -- hence, noise gating. Values <
            1.0 are possible, but it means that a very low-level
            control signal will cause the input signal to be
            amplified, which would raise the noise floor.

slopeAbove: Same thing, but above the threshold. Values < 1.0
            achieve compression (louder signals are attenuated) >
            1.0, you get expansion (louder signals are made even
            louder). For 3:1 compression, you would use a value of
            1/3 here.

clampTime: The amount of time it takes for the amplitude adjustment
           to kick in fully. This is usually pretty small, not much
           more than 10 milliseconds (the default value).

relaxTime: The amount of time for the amplitude adjustment to be
           released. Usually a bit longer than clampTime if both
           times are too short, you can get some (possibly
           unwanted) artifacts.

Example signal to process.

(define z
  (mul (decay2 (mul (impulse ar 8 0) (mul (lf-saw kr 0.3 0) 0.3)) 0.001 0.3)
       (mix (pulse ar (mce2 80 81) 0.3))))

(audition (out 0 z))

Noise gate

(let ((x (mouse-x kr 0.01 1 0 0.1)))
  (audition (out 0 (mce2 z (compander z z x 10 1 0.01 0.01)))))

Compressor

(let ((x (mouse-x kr 0.01 1 0 0.1)))
  (audition (out 0 (mce2 z (compander z z x 1 0.5 0.01 0.01)))))

limiter

(let ((x (mouse-x kr 0.01 1 0 0.1)))
  (audition (out 0 (mce2 z (compander z z x 1 0.1 0.01 0.01)))))

Sustainer

(let ((x (mouse-x kr 0.01 1 0 0.1)))
  (audition (out 0 (mce2 z (compander z z x 0.1 1.0 0.01 0.01)))))