gain.c

linux下的一款播放器

/* ***** BEGIN LICENSE BLOCK *****
 * Source last modified: $Id: gain.c,v 1.2.4.1 2004/07/09 02:02:24 hubbe Exp $
 * 
 * Portions Copyright (c) 1995-2004 RealNetworks, Inc. All Rights Reserved.
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 * the file under the current version of the RealNetworks Community
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 * ***** END LICENSE BLOCK ***** */

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

#include "gain.h"
#include "math64.h"

struct GAIN_STATE
{
    int sampleRate ;
    int nChannels ;
    int headRoom ;
    INT32 instGain ; /* gain applied right now */
    INT32 tgtGain ;  /* in a smooth gain change, the gain we are aiming for */
    int shift ;
} ;

enum
{
    zeroDBGain = (1L<<30)
} ;

GAIN_STATE* gainInit(int sampleRate, int nChannels, int headRoom)
{
    GAIN_STATE* g = (GAIN_STATE*) calloc(1,sizeof(GAIN_STATE)) ;
    if (g)
    {
        g->sampleRate = sampleRate ;
        g->nChannels = nChannels ;
        g->headRoom = headRoom ;
        gainSetTimeConstant(0.1f, g) ;
    }

    return g ;
}

void gainFree(GAIN_STATE* g)
{
    if (g) free(g) ;
}

float gainSetSmooth(float dB, GAIN_STATE* g)
{
    unsigned int gain = (unsigned int)(0.5 + (double)(1UL<<(30-g->headRoom)) * pow(10.0, 0.05*dB)) ;

    if (dB > 20.0 * log10(1<<g->headRoom))
    {
        gain = zeroDBGain; dB = 20.0f * (float)log10(1<<g->headRoom) ; // avoid overflow
    }

    g->tgtGain = (INT32)gain ;

    return dB ;
}

float gainSetImmediate(float dB, GAIN_STATE* g)
{
    dB = gainSetSmooth(dB, g) ;

    g->instGain = g->tgtGain ; // make it instantaneous

    return dB ;
}

int gainSetTimeConstant(float millis, GAIN_STATE* g)
{
    // we define the time constant millis so that the signal has decayed to 1/2 (-6dB) after
    // millis milliseconds have elapsed.
    // Let T[sec] = millis/1000 = time constant in units of seconds
    //
    // => (1-2^-s)^(T[sec]*sr) = 1/2
    // => 1-2^-s = (1/2)^(1/(T[sec]*sr))
    // => 2^-s = 1 - (1/2)^(1/(T[sec]*sr))
    // => s = -log2(1 - (1/2)^(1 / (T[sec]*sr)))

    // first 0.5 is rounding constant
    g->shift = (int)(0.5 - 1.0/log(2.0)*log(1.0 - pow(0.5, 1000.0/(millis * g->sampleRate)))) ;
    if (g->shift < 1)
        g->shift = 1 ;
    if (g->shift > 31)
        g->shift = 31 ;

    return 1 ; // OK
}

static void gainFeedMono(INT32* signal, int nSamples, GAIN_STATE *g)
{
    INT32 tgtGain = g->tgtGain ;
    INT32 gain = g->instGain ;
    INT32 *bufferEnd = signal + nSamples ;

    if (gain == tgtGain)
    { // steady state
	while (signal != bufferEnd)
	{
	    *signal = MulShift30(*signal, gain) ; signal++ ;
	}
    }
    else
    { // while we are still ramping the gain
        int shift = g->shift ;
	while (signal != bufferEnd)
	{
	    int rc = (tgtGain > gain) - (tgtGain < gain) ; // -1,0,1 for x<y, x=y, x>y
	    *signal = MulShift30(*signal, gain) ; signal++ ;
	    gain += ((tgtGain-gain) >> shift) + rc ;
	}
        g->instGain = gain ;
    }
}

static void gainFeedStereo(INT32* signal, int nSamples, GAIN_STATE *g)
{
    INT32 tgtGain = g->tgtGain ;
    INT32 gain = g->instGain ;
    INT32 *bufferEnd = signal + nSamples ;

    HX_ASSERT(nSamples % 2 == 0);

    if (gain == tgtGain)
    { // steady state
	while (signal != bufferEnd)
	{
	    *signal = MulShift30(*signal, gain) ; signal++ ;
	    *signal = MulShift30(*signal, gain) ; signal++ ;
	}
    }
    else
    { // while we are still ramping the gain
        int shift = g->shift ;
	while (signal != bufferEnd)
	{
	    int rc = (tgtGain > gain) - (tgtGain < gain) ; // -1,0,1 for x<y, x=y, x>y
	    *signal = MulShift30(*signal, gain) ; signal++ ;
	    *signal = MulShift30(*signal, gain) ; signal++ ;
	    gain += ((tgtGain-gain) >> shift) + rc ;
	}
        g->instGain = gain ;
    }
}

static void gainFeedMulti(INT32* signal, int nSamples, GAIN_STATE *g)
{
    INT32 tgtGain = g->tgtGain ;
    INT32 gain = g->instGain ;
    INT32 *bufferEnd = signal + nSamples ;

    HX_ASSERT(nSamples % g->nChannels == 0);

    if (gain == tgtGain)
    { // steady state
	while (signal != bufferEnd)
	{
	    int i ;
	    for (i = 0 ; i < g->nChannels ; i++)
	    {
		*signal = MulShift30(*signal, gain) ; signal++ ;
	    }
	}
    }
    else
    { // while we are still ramping the gain
        int shift = g->shift ;
	while (signal != bufferEnd)
	{
	    int rc = (tgtGain > gain) - (tgtGain < gain) ; // -1,0,1 for x<y, x=y, x>y
	    int i ;
	    for (i = 0 ; i < g->nChannels ; i++)
	    {
		*signal = MulShift30(*signal, gain) ; signal++ ;
	    }
	    gain += ((tgtGain-gain) >> shift) + rc ;
	}
        g->instGain = gain ;
    }
}

void gainFeed(INT32* signal, int nSamples, GAIN_STATE* g)
{
    /* if the gain is 0dB, and we are not currently ramping, shortcut. */
    if (g->instGain == zeroDBGain && g->instGain == g->tgtGain)
    {
        return ;
    }
    switch (g->nChannels)
    {
    case 1:
        gainFeedMono(signal, nSamples, g) ;
        break ;
    case 2:
        gainFeedStereo(signal, nSamples, g) ;
        break ;
    default:
        gainFeedMulti(signal, nSamples, g) ;
        break ;
    }
}