ref: 5e0e521494ba5c31589875497a1daa868ae19c92
dir: /src/bandpass.c/
/* Band-pass effect file for SoX Copyright (C) 1999 Jan Paul Schmidt <jps@fundament.org> This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This library 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 Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Code based on the band-pass implementation in Sound Processing Kit - A C++ Class Library for Audio Signal Processing Copyright (C) 1995-1998 Kai Lassfolk as described in Computer music: synthesis, composition, and performance Charles Dodge, Thomas A. Jerse [2nd ed.] Page 216 */ #include <math.h> #include "st_i.h" #include "btrworth.h" int st_bandpass_getopts (eff_t effp, int n, char **argv) { butterworth_t butterworth = (butterworth_t)effp->priv; if (n != 2) { st_fail("Usage: bandpass FREQUENCY BANDWIDTH"); return (ST_EOF); } st_butterworth_start (effp); if (!(sscanf (argv [0], "%lf", &butterworth->frequency))) { st_fail("bandpass: illegal frequency"); return (ST_EOF); } if (!(sscanf (argv [1], "%lf", &butterworth->bandwidth))) { st_fail("bandpass: illegal bandwidth"); return (ST_EOF); } return (ST_SUCCESS); } int st_bandpass_start (eff_t effp) { butterworth_t butterworth = (butterworth_t) effp->priv; double c; double d; c = 1.0 / tan (M_PI * butterworth->bandwidth / effp->ininfo.rate); d = 2 * cos (2 * M_PI * butterworth->frequency / effp->ininfo.rate); butterworth->a [0] = 1.0 / (1.0 + c); butterworth->a [1] = 0.0; butterworth->a [2] = -butterworth->a [0]; butterworth->b [0] = -c * d * butterworth->a [0]; butterworth->b [1] = (c - 1.0) * butterworth->a[0]; return (ST_SUCCESS); }