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