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/* Libvisual-plugins - Standard plugins for libvisual
*
* Copyright (C) 2004, 2005, 2006 Antti Silvast <asilvast@iki.fi>
*
* Authors: Antti Silvast <asilvast@iki.fi>
* Dennis Smit <ds@nerds-incorporated.org>
*
* $Id: notch.c,v 1.3 2006/01/22 13:25:26 synap Exp $
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include <stdio.h>
#include <math.h>
#include <string.h>
#include "notch.h"
NOTCH_FILTER * init_notch(float cutoff) {
NOTCH_FILTER * l=malloc(sizeof(NOTCH_FILTER));
float steep = 0.99;;
float r = steep * 0.99609375;
float f = cos(M_PI * cutoff / SAMPLING_RATE);
l->cutoff = cutoff;
l->a0 = (1 - r) * sqrt( r * (r - 4 * (f * f) + 2) + 1);
l->b1 = 2 * f * r;
l->b2 = -(r * r);
l->x1 = 0.0;
l->x2 = 0.0;
return l;
}
float process_notch(NOTCH_FILTER * l, float x0) {
float outp = l->a0 * x0 + l->b1 * l->x1 + l->b2 * l->x2;
l->x2 = l->x1;
l->x1 = outp;
return outp;
}
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