ddf.minim.effects
Class IIRFilter

java.lang.Object
  ddf.minim.ugens.UGen
      ddf.minim.effects.IIRFilter

All Implemented Interfaces:

AudioEffect

Direct Known Subclasses:

BandPass, ChebFilter, HighPassSP, LowPassFS, LowPassSP, NotchFilter

public abstract class IIRFilter
extends UGen
implements AudioEffect

An Infinite Impulse Response, or IIR, filter is a filter that uses a set of coefficients and previous filtered values to filter a stream of audio. It is an efficient way to do digital filtering. IIRFilter is a general IIRFilter that simply applies the filter designated by the filter coefficients so that sub-classes only have to dictate what the values of those coefficients are by defining the calcCoeff() function. When filling the coefficient arrays, be aware that b[0] corresponds to b1.

Author:

Damien Di Fede

Nested Class Summary

Nested classes/interfaces inherited from class ddf.minim.ugens.UGen

UGen.InputType, UGen.UGenInput

Field Summary

protected float[]	a The a coefficients.
UGen.UGenInput	audio
protected float[]	b The b coefficients.
UGen.UGenInput	cutoff

Constructor Summary

IIRFilter(float freq, float sampleRate)
Constructs an IIRFilter with the given cutoff frequency that will be used to filter audio recorded at sampleRate.

Method Summary

protected abstract void	calcCoeff() Calculates the coefficients of the filter using the current cutoff frequency.
float	frequency() Returns the cutoff frequency (in Hz).
protected void	initArrays(int numChannels) Initializes the in and out arrays based on the number of coefficients being used.
void	printCoeff() Prints the current values of the coefficients to the console.
void	process(float[] signal) Processes signal in some way.
void	process(float[] sigLeft, float[] sigRight) Processes sigLeft and sigRight in some way.
void	setFreq(float f) Sets the cutoff/center frequency of the filter.
void	uGenerate(float[] channels) Implement this method when you extend UGen.
boolean	validFreq(float f) Returns true if the frequency is valid for this filter.

Methods inherited from class ddf.minim.ugens.UGen

addInput, getLastValues, patch, patch, patch, printInputs, removeInput, sampleRate, sampleRateChanged, setSampleRate, tick, unpatch, unpatch

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

audio

public final UGen.UGenInput audio

cutoff

public final UGen.UGenInput cutoff

a

protected float[] a

The a coefficients.

b

protected float[] b

The b coefficients.

Constructor Detail

IIRFilter

public IIRFilter(float freq,
                 float sampleRate)

Constructs an IIRFilter with the given cutoff frequency that will be used to filter audio recorded at sampleRate.

Parameters:

freq - the cutoff frequency

sampleRate - the sample rate of audio to be filtered

Method Detail

initArrays

protected final void initArrays(int numChannels)

Initializes the in and out arrays based on the number of coefficients being used.

uGenerate

public final void uGenerate(float[] channels)

Description copied from class: UGen

Implement this method when you extend UGen. It will be called when your UGen needs to generate one sample frame of audio. It is expected that you will assign values to the array and not simply modify the existing values. In the case where you write a UGen that takes audio input and modifies it, the pattern to follow is to have the first UGenInput you create be your audio input and then in uGenerate you will use the getLastValues method of your audio UGenInput to retrieve the audio you want to modify, which you will then modify however you need to, assigning the result to the values in channels.

Specified by:

uGenerate in class UGen

Parameters:

channels - an array representing one sample frame.

process

public final void process(float[] signal)

Description copied from interface: AudioEffect

Processes signal in some way.

Specified by:

process in interface AudioEffect

Parameters:

signal - an array of audio samples, representing a mono sound stream.

process

public final void process(float[] sigLeft,
                          float[] sigRight)

Description copied from interface: AudioEffect

Processes sigLeft and sigRight in some way.

Specified by:

process in interface AudioEffect

Parameters:

sigLeft - an array of audio samples, representing the left channel of a stereo sound stream

sigRight - an array of audio samples, representing the right channel of a stereo sound stream

setFreq

public final void setFreq(float f)

Sets the cutoff/center frequency of the filter. Doing this causes the coefficients to be recalculated.

Parameters:

f - the new cutoff/center frequency (in Hz).

validFreq

public boolean validFreq(float f)

Returns true if the frequency is valid for this filter. Subclasses can override this method if they want to limit center frequencies to certain ranges to avoid becoming unstable. The default implementation simply makes sure that f is positive.

Parameters:

f - the frequency (in Hz) to validate

Returns:

true if f is a valid frequency for this filter

frequency

public final float frequency()

Returns the cutoff frequency (in Hz).

Returns:

the current cutoff frequency (in Hz).

calcCoeff

protected abstract void calcCoeff()

Calculates the coefficients of the filter using the current cutoff frequency. To make your own IIRFilters, you must extend IIRFilter and implement this function. The frequency is expressed as a fraction of the sample rate. When filling the coefficient arrays, be aware that b[0] corresponds to the coefficient b1.

printCoeff

public final void printCoeff()

Prints the current values of the coefficients to the console.