134 lines
4.1 KiB
C
134 lines
4.1 KiB
C
/*
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* Copyright (C) 2002-2006 Felipe Rivera <liebremx at users.sourceforge.net>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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*
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* Coefficient stuff
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*
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* $Id: iir_cfs.c,v 1.2 2006/01/15 00:17:46 liebremx Exp $
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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static const double band_f031[] =
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{ 20,25,31.5,40,50,63,80,100,125,160,200,250,315,400,500,630,800,
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1000,1250,1600,2000,2500,3150,4000,5000,6300,8000,10000,12500,16000,20000
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};
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#define GAIN_F0 1.0
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#define GAIN_F1 GAIN_F0 / M_SQRT2
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#define SAMPLING_FREQ 44100.0
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#define TETA(f) (2*M_PI*(double)f/sample_frequency)
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#define TWOPOWER(value) (value * value)
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#define BETA2(tf0, tf) \
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(TWOPOWER(GAIN_F1)*TWOPOWER(cos(tf0)) \
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- 2.0 * TWOPOWER(GAIN_F1) * cos(tf) * cos(tf0) \
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+ TWOPOWER(GAIN_F1) \
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- TWOPOWER(GAIN_F0) * TWOPOWER(sin(tf)))
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#define BETA1(tf0, tf) \
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(2.0 * TWOPOWER(GAIN_F1) * TWOPOWER(cos(tf)) \
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+ TWOPOWER(GAIN_F1) * TWOPOWER(cos(tf0)) \
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- 2.0 * TWOPOWER(GAIN_F1) * cos(tf) * cos(tf0) \
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- TWOPOWER(GAIN_F1) + TWOPOWER(GAIN_F0) * TWOPOWER(sin(tf)))
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#define BETA0(tf0, tf) \
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(0.25 * TWOPOWER(GAIN_F1) * TWOPOWER(cos(tf0)) \
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- 0.5 * TWOPOWER(GAIN_F1) * cos(tf) * cos(tf0) \
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+ 0.25 * TWOPOWER(GAIN_F1) \
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- 0.25 * TWOPOWER(GAIN_F0) * TWOPOWER(sin(tf)))
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#define GAMMA(beta, tf0) ((0.5 + beta) * cos(tf0))
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#define ALPHA(beta) ((0.5 - beta)/2.0)
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/*************
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* Functions *
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*************/
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/* Get the band_f031 at both sides of F0. These will be cut at -3dB */
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static void find_f1_and_f2(double f0, double octave_percent, double *f1, double *f2)
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{
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double octave_factor = pow(2.0, octave_percent/2.0);
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*f1 = f0/octave_factor;
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*f2 = f0*octave_factor;
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}
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/* Find the quadratic root
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* Always return the smallest root */
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static int find_root(double a, double b, double c, double *x0) {
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double k = c-((b*b)/(4.*a));
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double h = -(b/(2.*a));
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double x1 = 0.;
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if (-(k/a) < 0.)
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return -1;
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*x0 = h - sqrt(-(k/a));
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x1 = h + sqrt(-(k/a));
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if (x1 < *x0)
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*x0 = x1;
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return 0;
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}
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void calc_coeffs(double sample_frequency)
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{
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int i, n;
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double f1, f2;
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double x0;
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printf(" public final static IIRCoefficients iir_cf31_%d[] = {\n", (int)sample_frequency);
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for (i = 0; i < 31; i++) {
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/* Find -3dB frequencies for the center freq */
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find_f1_and_f2(band_f031[i], 1.0/3.0, &f1, &f2);
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/* Find Beta */
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if ( find_root(
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BETA2(TETA(band_f031[i]), TETA(f1)),
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BETA1(TETA(band_f031[i]), TETA(f1)),
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BETA0(TETA(band_f031[i]), TETA(f1)),
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&x0) == 0)
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{
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/* Got a solution, now calculate the rest of the factors */
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/* Take the smallest root always (find_root returns the smallest one)
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*
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* NOTE: The IIR equation is
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* y[n] = 2 * (alpha*(x[n]-x[n-2]) + gamma*y[n-1] - beta*y[n-2])
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* Now the 2 factor has been distributed in the coefficients
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*/
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/* Now store the coefficients */
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printf(" /* %.1f Hz */\n", band_f031[i]);
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printf(" new IIRCoefficients(%.10e, %010e, %.10e),\n",
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(double)(2.0 * x0),
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(double)(2.0 * ALPHA(x0)),
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(double)(2.0 * GAMMA(x0, TETA(band_f031[i])))
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);
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} else {
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printf(" **** Where are the roots?\n");
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}
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}// for i
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printf(" };\n");
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}
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int main(int argc, char **argv) {
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if (argc != 2) {
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printf("Usage: iircoeff <sample frequency>\n");
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return -1;
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}
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double f = strtod(argv[1], NULL);
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calc_coeffs(f);
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}
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