99 lines
1.8 KiB
Racket
99 lines
1.8 KiB
Racket
#lang scribble/manual
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@(require (for-label racket))
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@title{Median}
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Median filter.@section{categories}
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UGens>Filters>Nonlinear
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@section{description}
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Returns the median of the last length input points. This non-linear
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filter is good at reducing impulse noise from a signal.
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@section{classmethods}
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@section{method}
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ar, kr
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@section{argument}
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length
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Number of input points in which to find the median. Must be an
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odd number from 1 to 31. If
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@racketblock[length:: is 1
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then Median has no effect.
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]
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@section{argument}
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in
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The input signal.
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@section{argument}
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mul
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Output will be multiplied by this value.
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@section{argument}
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add
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This value will be added to the output.
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@section{Examples}
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@racketblock[
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// a signal with impulse noise.
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{ Saw.ar(500, 0.1) + Dust2.ar(100, 0.9) }.play;
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// after applying median filter
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{ Median.ar(3, Saw.ar(500, 0.1) + Dust2.ar(100, 0.9)) }.play;
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// The median length can be increased for longer duration noise.
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// a signal with longer impulse noise.
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{ Saw.ar(500, 0.1) + LPZ1.ar(Dust2.ar(100, 0.9)) }.play;
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// length 3 doesn't help here because the impulses are 2 samples long.
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{ Median.ar(3, Saw.ar(500, 0.1) + LPZ1.ar(Dust2.ar(100, 0.9))) }.play;
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// length 5 does better
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{ Median.ar(5, Saw.ar(500, 0.1) + LPZ1.ar(Dust2.ar(100, 0.9))) }.play;
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// long Median filters begin chopping off the peaks of the waveform
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(
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{
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x = SinOsc.ar(1000, 0, 0.2);
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[x, Median.ar(31, x)]
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}.play;
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)
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// another noise reduction application:
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Synth.play({ WhiteNoise.ar(0.1) + SinOsc.ar(800,0,0.1) });
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// use Median filter for high frequency noise
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Synth.play({ Median.ar(31, WhiteNoise.ar(0.1) + SinOsc.ar(800,0,0.1)) });
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(
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// use LeakDC for low frequency noise
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Synth.play({
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LeakDC.ar(Median.ar(31, WhiteNoise.ar(0.1) + SinOsc.ar(800,0,0.1)), 0.9)
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});
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)
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::
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]
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