ref: 628b719fe32e26dd16c0b5694acf046da160305e
dir: /src/btrworth.c/
/* Butterworth effect file for SoX Copyright (C) 1999 Jan Paul Schmidt <jps@fundament.org> This source code 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 source code 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 Library General Public License along with this library; if not, write to the Free Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Code based on the butterworth 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 214 */ #include <math.h> #include "st_i.h" #include "btrworth.h" int st_butterworth_start (eff_t effp) { butterworth_t butterworth = (butterworth_t) effp->priv; butterworth->x [0] = 0.0; butterworth->x [1] = 0.0; butterworth->y [0] = 0.0; butterworth->y [1] = 0.0; return (ST_SUCCESS); } int st_butterworth_flow (eff_t effp, st_sample_t *ibuf, st_sample_t *obuf, st_size_t *isamp, st_size_t *osamp) { butterworth_t butterworth = (butterworth_t) effp->priv; double in; double out; int len; int done; len = ((*isamp > *osamp) ? *osamp : *isamp); for (done = 0; done < len; done++) { in = *ibuf++; /* * Substituting butterworth->a [x] and butterworth->b [x] with * variables, which are set outside of the loop, did not increased * speed on my AMD Box. GCC seems to do a good job :o) */ out = butterworth->a [0] * in + butterworth->a [1] * butterworth->x [0] + butterworth->a [2] * butterworth->x [1] - butterworth->b [0] * butterworth->y [0] - butterworth->b [1] * butterworth->y [1]; butterworth->x [1] = butterworth->x [0]; butterworth->x [0] = in; butterworth->y [1] = butterworth->y [0]; butterworth->y [0] = out; if (out < ST_SAMPLE_MIN) { out = ST_SAMPLE_MIN; } else if (out > ST_SAMPLE_MAX) { out = ST_SAMPLE_MAX; } *obuf++ = out; } *isamp = len; *osamp = len; return (ST_SUCCESS); }