gain.c

Intercom 是一个 Unix系统上灵活的语音传输软件。支持标准音频压缩比如GSM, G.711, and G.72x和其他音频编码。Intercom专为高速网络设计来传输高品质的语音

/*  gain.c -- Gain control routines
    Copyright (C) 2001-2003  Shane Wegner
    This file is part of Intercom.

    Intercom is free software; you can redistribute it and/or modify it
    under the terms of version 2 of the GNU General Public License as
    published by the Free Software Foundation.

    Intercom 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 version 2 of the GNU General Public
    License along with Intercom; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

    To contact the author, please send email to [e-mail].
    */
/* $Id: gain.c,v 1.2 2003/02/13 20:22:49 shane Exp $ */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdlib.h>
#include <math.h>

#include <gain.h>

#ifndef ROUND
# define ROUND(x) floor((x) + 0.5)
#endif
#define DBTOFRAC(x) pow(10,(x)/20.0)
static double lmtr_lvl = 0.5;

/*
 * Limiter function:
 *
 *        / tanh((x + lev) / (1-lev)) * (1-lev) - lev        (for x < -lev)
 *        |
 *   x' = | x                                                (for |x| <= lev)
 *        |
 *        \ tanh((x - lev) / (1-lev)) * (1-lev) + lev        (for x > lev)
 *
 * With limiter level = 0, this is equivalent to a tanh() function;
 * with limiter level = 1, this is equivalent to clipping.
 */
static double limiter(double x)
{
double xp;
  if (x < -lmtr_lvl)
    xp = tanh((x + lmtr_lvl) / (1-lmtr_lvl)) * (1-lmtr_lvl) - lmtr_lvl;
  else if (x <= lmtr_lvl)
    xp = x;
  else
    xp = tanh((x - lmtr_lvl) / (1-lmtr_lvl)) * (1-lmtr_lvl) + lmtr_lvl;
  return xp;
}

static void gain_buildtable(struct gain *handle)
{
#define SAMPLEMIN -32768
#define SAMPLEMAX 32767
int i;
if (handle->gain > 1.0) { /* gain with limiter */
for (i = SAMPLEMIN; i < 0; i++)
handle->tblp[i] = ROUND(-SAMPLEMIN * limiter(i * handle->gain / (double)-SAMPLEMIN));
for (; i <= SAMPLEMAX; i++)
handle->tblp[i] = ROUND(SAMPLEMAX * limiter(i * handle->gain / (double)SAMPLEMAX));
} else { /* no limiter if gain is negative */
for (i = SAMPLEMIN; i <= SAMPLEMAX; i++)
handle->tblp[i] = i * handle->gain;
}
}

struct gain *gain_init(double gain)
{
struct gain *g = malloc(sizeof(struct gain));
g->gain = DBTOFRAC(gain);
g->gain_db = gain;
g->tbl = malloc(sizeof(short) * 65536);
g->tblp = g->tbl + 32768;
gain_buildtable(g);
return g;
}

void gain_update(struct gain *handle, double gain)
{
handle->gain = DBTOFRAC(gain);
handle->gain_db = gain;
gain_buildtable(handle);
}

void gain_apply(struct gain *handle, short *buff, size_t samples)
{
size_t i;
for (i = 0; i < samples; i++)
buff[i] = handle->tblp[buff[i]];
}

void gain_free(struct gain *handle)
{
free(handle->tbl);
free(handle);
}