AmpComp | SuperCollider 3.13.0 Help

Source: Line.sc

Subclasses: AmpCompA

Description

Implements the (optimized) formula:compensationFactor = (root / freq) ** exp

Higher frequencies are normally perceived as louder, which AmpComp compensates.

Class Methods

AmpComp.ar(freq, root, exp: 0.3333)

AmpComp.kr(freq, root, exp: 0.3333)

AmpComp.ir(freq, root, exp: 0.3333)

Arguments:

freq	Input frequency value. For freq == root, the output is 1.0.
root	Root freq relative to which the curve is calculated (usually lowest freq).
exp	Exponent: how steep the curve decreases for increasing freq.

Discussion:

Note that for frequencies very much smaller than root the amplitudes can become very high. In this case limit the freq with freq.max(minval), or use AmpCompA.

Examples

// compare a sine without compensation

{ SinOsc.ar(MouseX.kr(300, 15000, 1)) * 0.1 }.play;

// with one that uses amplitude compensation
(
{
    var freq;
    freq = MouseX.kr(300, 15000, 1);
    SinOsc.ar(freq) * 0.1 * AmpComp.kr(freq, 300)
}.play;
)

// different sounds cause quite different loudness perception,
// and the desired musical behavior can vary, so the exponent can be tuned:
(
{
    var freq;
    freq = MouseX.kr(300, 15000, 1);
    Pulse.ar(freq) * 0.1 * AmpComp.kr(freq, 300, 1.3)
}.play;
)

// the curves:

// exp = 0.3333
(200,210..10000).collect {|freq| (200/freq) ** 0.3333 }.plot;

// nearly linear for semitone steps:

(48..72).midicps.collect {|freq| (48.midicps/freq) ** 0.3333 }.plot;
{ AmpComp.ar(Line.ar(48, 72, 1).midicps, 48.midicps) }.plot(1.0);

// exp = 1.2
(200,210..10000).collect {|freq| (200/freq) ** 1.2 }.plot;
(48..72).midicps.collect {|freq| (200/freq) ** 1.2 }.plot;
{ AmpComp.ar(Line.ar(48, 72, 1).midicps, 48.midicps, 1.2) }.plot(1.0);

// amplitude compensation in frequency modulation
(
{
    var freq;
    freq = MouseX.kr(300, 15000, 1);
    freq = freq * SinOsc.ar(MouseY.kr(3, 200, 1), 0, 0.5, 1);
    SinOsc.ar(freq) * 0.1 * AmpComp.ar(freq, 300)
}.play;
)

// without amplitude compensation
(
{
    var freq;
    freq = MouseX.kr(300, 15000, 1);
    freq = freq * SinOsc.ar(MouseY.kr(3, 200, 1), 0, 0.5, 1);
    SinOsc.ar(freq) * 0.1
}.play;
)

// in granular synthesis:
(
SynthDef("pgrain",
    { arg out = 0, sustain=0.01, amp=0.5, pan = 0;
        var freq = MouseX.kr(300, 7000, 1);
        var window = Env.sine(sustain, amp * AmpComp.ir(freq));
        Out.ar(out,
            Pan2.ar(
                SinOsc.ar(freq),
                pan
            ) * EnvGen.ar(window, doneAction: Done.freeSelf)
        )
    }
).add;
)

// send grains
(
fork {
    loop {
        s.sendBundle(0.1, [\s_new, \pgrain, -1,1,1]);
        0.02.wait;
    };
}
)

// try different synth defs:

// without AmpComp:

(
SynthDef("pgrain",
    { arg out = 0, sustain=0.01, amp=0.5, pan = 0;
        var freq = MouseX.kr(300, 7000, 1);
        var window = Env.sine(sustain, amp);
        Out.ar(out,
            Pan2.ar(
                SinOsc.ar(freq),
                pan
            ) * EnvGen.ar(window, doneAction: Done.freeSelf)
        )
    }
).add;
)

// with AmpCompA
(
SynthDef("pgrain",
    { arg out = 0, sustain=0.01, amp=0.5, pan = 0;
        var freq = MouseX.kr(300, 7000, 1);
        var window = Env.sine(sustain, amp * AmpCompA.ir(freq));
        Out.ar(out,
            Pan2.ar(
                SinOsc.ar(freq),
                pan
            ) * EnvGen.ar(window, doneAction: Done.freeSelf)
        )
    }
).add;
)

helpfile source: https://github.com/supercollider/supercollider/tree/3.13/HelpSource/Classes/AmpComp.schelp
link::Classes/AmpComp::

AmpComp : PureUGen : UGen : AbstractFunction : Object