/* libSoX effect: Hilbert transform filter * * First version of this effect written 11/2011 by Ulrich Klauer, using maths * from "Understanding digital signal processing" by Richard G. Lyons. * * Copyright 2011 Chris Bagwell and SoX Contributors * * 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 2.1 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA */ #include "sox_i.h"#include "dft_filter.h" typedef struct {  dft_filter_priv_t base;  double *h;  int taps;} priv_t; static int getopts(sox_effect_t *effp, int argc, char **argv){  lsx_getopt_t optstate;  int c;  priv_t *p = (priv_t*)effp->priv;  dft_filter_priv_t *b = &p->base;   b->filter_ptr = &b->filter;   lsx_getopt_init(argc, argv, "+n:", NULL, lsx_getopt_flag_none, 1, &optstate);   while ((c = lsx_getopt(&optstate)) != -1) switch (c) {    GETOPT_NUMERIC(optstate, 'n', taps, 3, 32767)    default: lsx_fail("invalid option `-%c'", optstate.opt); return lsx_usage(effp);  }  if (p->taps && p->taps%2 == 0) {    lsx_fail("only filters with an odd number of taps are supported");    return SOX_EOF;  }  return optstate.ind != argc ? lsx_usage(effp) : SOX_SUCCESS;} static int start(sox_effect_t *effp){  priv_t *p = (priv_t*)effp->priv;  dft_filter_t *f = p->base.filter_ptr;   if (!f->num_taps) {    int i;    if (!p->taps) {      p->taps = effp->in_signal.rate/76.5 + 2;      p->taps += 1 - (p->taps%2);      /* results in a cutoff frequency of about 75 Hz with a Blackman window */      lsx_debug("choosing number of taps = %d (override with -n)", p->taps);    }    lsx_valloc(p->h, p->taps);    for (i = 0; i < p->taps; i++) {      int k = -(p->taps/2) + i;      if (k%2 == 0) {        p->h[i] = 0.0;      } else {        double pk = M_PI * k;        p->h[i] = (1 - cos(pk))/pk;      }    }    lsx_apply_blackman(p->h, p->taps, .16);     if (effp->global_info->plot != sox_plot_off) {      char title[100];      sprintf(title, "SoX effect: hilbert (%d taps)", p->taps);      lsx_plot_fir(p->h, p->taps, effp->in_signal.rate,          effp->global_info->plot, title, -20., 5.);      free(p->h);      return SOX_EOF;    }    lsx_set_dft_filter(f, p->h, p->taps, p->taps/2);  }  return lsx_dft_filter_effect_fn()->start(effp);} sox_effect_handler_t const *lsx_hilbert_effect_fn(void){  static sox_effect_handler_t handler;  handler = *lsx_dft_filter_effect_fn();  handler.name = "hilbert";  handler.usage = "[-n taps]";  handler.getopts = getopts;  handler.start = start;  handler.priv_size = sizeof(priv_t);  return &handler;}