/*
* Copyright (c) 2007 by Damien Di Fede <ddf@compartmental.net>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Library General Public License as published
* by the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
package ddf.minim.effects;
/**
* A notch filter removes a narrow band of frequencies from an audio signal. It
* is the opposite of a band pass filter, which allows only a narrow band of
* frequencies to pass through the filter.
*
* @author Damien Di Fede
*
*/
public class NotchFilter extends IIRFilter
{
private float bw;
/**
* Constructs a notch filter with the requested center frequency, bandwidth and
* sample rate.
*
* @param freq the center frequency of the band to remove (in Hz)
* @param bandWidth the width of the band to remove (in Hz)
* @param sampleRate the sample rate of audio that will be filtered by this filter
*/
public NotchFilter(float freq, float bandWidth, float sampleRate)
{
super(freq, sampleRate);
setBandWidth(bandWidth);
}
/**
* Sets the band width of the filter.
*
* @param b the band width (in Hz)
*/
public void setBandWidth(float b)
{
bw = b / sampleRate();
}
/**
* Returns the band width of this filter.
*
* @return the band width (in Hz)
*/
public float getBandWidth()
{
return bw * sampleRate();
}
protected void calcCoeff()
{
float fracFreq = frequency()/sampleRate();
float R = 1 - 3 * bw;
float T = 2 * (float) Math.cos(2 * Math.PI * fracFreq);
float K = (1 - R * T + R * R) / (2 - T);
a = new float[] { K, -K * T, K };
b = new float[] { R * T, -R * R };
}
}