shithub: aacdec

ref: d6839757dffdf592ae300726a64e0f3199a9cd56
dir: /libfaad/drc.c/

/*
** FAAD - Freeware Advanced Audio Decoder
** Copyright (C) 2002 M. Bakker
**  
** This program 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 program 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 General Public License
** along with this program; if not, write to the Free Software 
** Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
**
** $Id: drc.c,v 1.4 2002/03/16 13:38:37 menno Exp $
**/

#include "common.h"

#include <memory.h>
#include "syntax.h"
#include "drc.h"

void init_drc(drc_info *drc, real_t cut, real_t boost)
{
    memset(drc, 0, sizeof(drc_info));

    drc->ctrl1 = cut;
    drc->ctrl2 = boost;

    drc->num_bands = 1;
    drc->band_top[0] = 1024/4 - 1;
    drc->dyn_rng_sgn[0] = 1;
    drc->dyn_rng_ctl[0] = 0;
}

void drc_decode(drc_info *drc, real_t *spec)
{
    uint16_t i, bd, top;
    real_t factor;
    uint16_t bottom = 0;

    if (drc->num_bands == 1)
        drc->band_top[0] = 1024/4 - 1;

    for (bd = 0; bd < drc->num_bands; bd++)
    {
        top = 4 * (drc->band_top[bd] + 1);

        /* Decode DRC gain factor */
        if (drc->dyn_rng_sgn[bd])  /* compress */
            factor = (real_t)exp(LN2 * (-drc->ctrl1 * drc->dyn_rng_ctl[bd]/24.0));
        else /* boost */
            factor = (real_t)exp(LN2 * (drc->ctrl2 * drc->dyn_rng_ctl[bd]/24.0));

        /* Level alignment between different programs (if desired) */
        /* If program reference normalization is done in the digital domain,
           modify factor to perform normalization.
           prog_ref_level can alternatively be passed to the system for
           modification of the level in the analog domain. Analog level
           modification avoids problems with reduced DAC SNR (if signal is
           attenuated) or clipping (if signal is boosted)
         */
        factor *= (real_t)exp(LN05 * ((DRC_REF_LEVEL - drc->prog_ref_level)/24.0));

        /* Apply gain factor */
        for (i = bottom; i < top; i++)
            spec[i] *= factor;

        bottom = top;
    }
}