limiter.cpp - Android社区 - https://www.androidos.net.cn/

/* -----------------------------------------------------------------------------------------------------------
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Fraunhofer Institute for Integrated Circuits IIS
Attention: Audio and Multimedia Departments - FDK AAC LL
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www.iis.fraunhofer.de/amm
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----------------------------------------------------------------------------------------------------------- */

/************************  FDK PCM postprocessor module  *********************

Author(s):   Matthias Neusinger
   Description: Hard limiter for clipping prevention

*******************************************************************************/

#include "limiter.h"

struct TDLimiter {
  unsigned int  attack;
  FIXP_DBL      attackConst, releaseConst;
  unsigned int  attackMs, releaseMs, maxAttackMs;
  FIXP_PCM      threshold;
  unsigned int  channels, maxChannels;
  unsigned int  sampleRate, maxSampleRate;
  FIXP_DBL      cor, max;
  FIXP_DBL*     maxBuf;
  FIXP_DBL*     delayBuf;
  unsigned int  maxBufIdx, delayBufIdx;
  FIXP_DBL      smoothState0;
  FIXP_DBL      minGain;

FIXP_DBL      additionalGainPrev;
  FIXP_DBL      additionalGainFilterState;
  FIXP_DBL      additionalGainFilterState1;
};

/* create limiter */
TDLimiterPtr createLimiter(
                           unsigned int  maxAttackMs,
                           unsigned int  releaseMs,
                           INT_PCM       threshold,
                           unsigned int  maxChannels,
                           unsigned int  maxSampleRate
                           )
{
  TDLimiterPtr limiter = NULL;
  unsigned int attack, release;
  FIXP_DBL attackConst, releaseConst, exponent;
  INT e_ans;

/* calc attack and release time in samples */
  attack = (unsigned int)(maxAttackMs * maxSampleRate / 1000);
  release = (unsigned int)(releaseMs * maxSampleRate / 1000);

/* alloc limiter struct */
  limiter = (TDLimiterPtr)FDKcalloc(1, sizeof(struct TDLimiter));
  if (!limiter) return NULL;

/* alloc max and delay buffers */
  limiter->maxBuf   = (FIXP_DBL*)FDKcalloc(attack + 1, sizeof(FIXP_DBL));
  limiter->delayBuf = (FIXP_DBL*)FDKcalloc(attack * maxChannels, sizeof(FIXP_DBL));

if (!limiter->maxBuf || !limiter->delayBuf) {
    destroyLimiter(limiter);
    return NULL;
  }

/* attackConst = pow(0.1, 1.0 / (attack + 1)) */
  exponent = invFixp(attack+1);
  attackConst = fPow(FL2FXCONST_DBL(0.1f), 0, exponent, 0, &e_ans);
  attackConst = scaleValue(attackConst, e_ans);

/* releaseConst  = (float)pow(0.1, 1.0 / (release + 1)) */
  exponent = invFixp(release + 1);
  releaseConst = fPow(FL2FXCONST_DBL(0.1f), 0, exponent, 0, &e_ans);
  releaseConst = scaleValue(releaseConst, e_ans);

/* init parameters */
  limiter->attackMs      = maxAttackMs;
  limiter->maxAttackMs   = maxAttackMs;
  limiter->releaseMs     = releaseMs;
  limiter->attack        = attack;
  limiter->attackConst   = attackConst;
  limiter->releaseConst  = releaseConst;
  limiter->threshold     = (FIXP_PCM)threshold;
  limiter->channels      = maxChannels;
  limiter->maxChannels   = maxChannels;
  limiter->sampleRate    = maxSampleRate;
  limiter->maxSampleRate = maxSampleRate;

resetLimiter(limiter);

return limiter;
}

/* reset limiter */
TDLIMITER_ERROR resetLimiter(TDLimiterPtr limiter)
{
  if (limiter != NULL) {

limiter->maxBufIdx = 0;
    limiter->delayBufIdx = 0;
    limiter->max = (FIXP_DBL)0;
    limiter->cor = FL2FXCONST_DBL(1.0f/(1<<1));
    limiter->smoothState0 = FL2FXCONST_DBL(1.0f/(1<<1));
    limiter->minGain = FL2FXCONST_DBL(1.0f/(1<<1));

limiter->additionalGainPrev = FL2FXCONST_DBL(1.0f/(1<<TDL_GAIN_SCALING));
    limiter->additionalGainFilterState = FL2FXCONST_DBL(1.0f/(1<<TDL_GAIN_SCALING));
    limiter->additionalGainFilterState1 = FL2FXCONST_DBL(1.0f/(1<<TDL_GAIN_SCALING));

FDKmemset(limiter->maxBuf,   0, (limiter->attack + 1) * sizeof(FIXP_DBL) );
    FDKmemset(limiter->delayBuf, 0, limiter->attack * limiter->channels * sizeof(FIXP_DBL) );
  }
  else {
    return TDLIMIT_INVALID_HANDLE;
  }

return TDLIMIT_OK;
}

/* destroy limiter */
TDLIMITER_ERROR destroyLimiter(TDLimiterPtr limiter)
{
  if (limiter != NULL) {
    FDKfree(limiter->maxBuf);
    FDKfree(limiter->delayBuf);

FDKfree(limiter);
  }
  else {
    return TDLIMIT_INVALID_HANDLE;
  }
  return TDLIMIT_OK;
}

/* apply limiter */
TDLIMITER_ERROR applyLimiter(TDLimiterPtr limiter,
                 INT_PCM*    samples,
                 FIXP_DBL*    pGain,
                 const INT*   gain_scale,
                 const UINT   gain_size,
                 const UINT   gain_delay,
                 const UINT   nSamples)
{
  unsigned int i, j;
  FIXP_PCM tmp1, tmp2;
  FIXP_DBL tmp, old, gain, additionalGain, additionalGainUnfiltered;
  FIXP_DBL minGain = FL2FXCONST_DBL(1.0f/(1<<1));

FDK_ASSERT(gain_size == 1);
  FDK_ASSERT(gain_delay <= nSamples);

if ( limiter == NULL ) return TDLIMIT_INVALID_HANDLE;

{
    unsigned int channels       = limiter->channels;
    unsigned int attack         = limiter->attack;
    FIXP_DBL     attackConst    = limiter->attackConst;
    FIXP_DBL     releaseConst   = limiter->releaseConst;
    FIXP_DBL     threshold      = FX_PCM2FX_DBL(limiter->threshold)>>TDL_GAIN_SCALING;

FIXP_DBL     max            = limiter->max;
    FIXP_DBL*    maxBuf         = limiter->maxBuf;
    unsigned int maxBufIdx      = limiter->maxBufIdx;
    FIXP_DBL     cor            = limiter->cor;
    FIXP_DBL*    delayBuf       = limiter->delayBuf;
    unsigned int delayBufIdx    = limiter->delayBufIdx;

FIXP_DBL     smoothState0   = limiter->smoothState0;
    FIXP_DBL     additionalGainSmoothState = limiter->additionalGainFilterState;
    FIXP_DBL     additionalGainSmoothState1 = limiter->additionalGainFilterState1;

for (i = 0; i < nSamples; i++) {

if (i < gain_delay) {
        additionalGainUnfiltered = limiter->additionalGainPrev;
      } else {
        additionalGainUnfiltered = pGain[0];
      }

/* Smooth additionalGain */
      /* [b,a] = butter(1, 0.01) */
      static const FIXP_SGL b[] = { FL2FXCONST_SGL(0.015466*2.0), FL2FXCONST_SGL( 0.015466*2.0) };
      static const FIXP_SGL a[] = { FL2FXCONST_SGL(1.000000), FL2FXCONST_SGL(-0.96907) };
      /* [b,a] = butter(1, 0.001) */
      //static const FIXP_SGL b[] = { FL2FXCONST_SGL(0.0015683*2.0), FL2FXCONST_SGL( 0.0015683*2.0) };
      //static const FIXP_SGL a[] = { FL2FXCONST_SGL(1.0000000), FL2FXCONST_SGL(-0.99686) };
      additionalGain = - fMult(additionalGainSmoothState, a[1]) + fMultDiv2( additionalGainUnfiltered, b[0]) + fMultDiv2(additionalGainSmoothState1, b[1]);
      additionalGainSmoothState1 = additionalGainUnfiltered;
      additionalGainSmoothState = additionalGain;

/* Apply the additional scaling that has no delay and no smoothing */
      if (gain_scale[0] > 0) {
        additionalGain <<= gain_scale[0];
      } else {
        additionalGain >>= gain_scale[0];
      }

/* get maximum absolute sample value of all channels, including the additional gain. */
      tmp1 = (FIXP_PCM)0;
      for (j = 0; j < channels; j++) {
          tmp2 = (FIXP_PCM)samples[i * channels + j];
          if (tmp2 == (FIXP_PCM)SAMPLE_MIN) /* protect fAbs from -1.0 value */
              tmp2 = (FIXP_PCM)(SAMPLE_MIN+1);
        tmp1 = fMax(tmp1, fAbs(tmp2));
      }
      tmp = SATURATE_LEFT_SHIFT(fMultDiv2(tmp1, additionalGain), 1, DFRACT_BITS);

/* set threshold as lower border to save calculations in running maximum algorithm */
      tmp = fMax(tmp, threshold);

/* running maximum */
      old = maxBuf[maxBufIdx];
      maxBuf[maxBufIdx] = tmp;

if (tmp >= max) {
        /* new sample is greater than old maximum, so it is the new maximum */
        max = tmp;
      }
      else if (old < max) {
        /* maximum does not change, as the sample, which has left the window was
           not the maximum */
      }
      else {
        /* the old maximum has left the window, we have to search the complete
           buffer for the new max */
        max = maxBuf[0];
        for (j = 1; j <= attack; j++) {
          if (maxBuf[j] > max) max = maxBuf[j];
        }
      }
      maxBufIdx++;
      if (maxBufIdx >= attack+1) maxBufIdx = 0;

/* calc gain */
      /* gain is downscaled by one, so that gain = 1.0 can be represented */
      if (max > threshold) {
        gain = fDivNorm(threshold, max)>>1;
      }
      else {
        gain = FL2FXCONST_DBL(1.0f/(1<<1));
      }

/* gain smoothing, method: TDL_EXPONENTIAL */
      /* first order IIR filter with attack correction to avoid overshoots */

/* correct the 'aiming' value of the exponential attack to avoid the remaining overshoot */
      if (gain < smoothState0) {
        cor = fMin(cor, fMultDiv2((gain - fMultDiv2(FL2FXCONST_SGL(0.1f*(1<<1)),smoothState0)), FL2FXCONST_SGL(1.11111111f/(1<<1)))<<2);
      }
      else {
        cor = gain;
      }

/* smoothing filter */
      if (cor < smoothState0) {
        smoothState0 = fMult(attackConst,(smoothState0 - cor)) + cor;  /* attack */
        smoothState0 = fMax(smoothState0, gain); /* avoid overshooting target */
      }
      else {
        /* sign inversion twice to round towards +infinity,
           so that gain can converge to 1.0 again,
           for bit-identical output when limiter is not active */
        smoothState0 = -fMult(releaseConst,-(smoothState0 - cor)) + cor; /* release */
      }

gain = smoothState0;

/* lookahead delay, apply gain */
      for (j = 0; j < channels; j++) {

tmp = delayBuf[delayBufIdx * channels + j];
        delayBuf[delayBufIdx * channels + j] = fMult((FIXP_PCM)samples[i * channels + j], additionalGain);

/* Apply gain to delayed signal */
        if (gain < FL2FXCONST_DBL(1.0f/(1<<1)))
          tmp = fMult(tmp,gain<<1);

samples[i * channels + j] = FX_DBL2FX_PCM((FIXP_DBL)SATURATE_LEFT_SHIFT(tmp,TDL_GAIN_SCALING,DFRACT_BITS));
      }
      delayBufIdx++;
      if (delayBufIdx >= attack) delayBufIdx = 0;

/* save minimum gain factor */
      if (gain < minGain) minGain = gain;
    }

limiter->max = max;
    limiter->maxBufIdx = maxBufIdx;
    limiter->cor = cor;
    limiter->delayBufIdx = delayBufIdx;

limiter->smoothState0 = smoothState0;
    limiter->additionalGainFilterState = additionalGainSmoothState;
    limiter->additionalGainFilterState1 = additionalGainSmoothState1;

limiter->minGain = minGain;

limiter->additionalGainPrev = pGain[0];

return TDLIMIT_OK;
  }
}

/* get delay in samples */
unsigned int getLimiterDelay(TDLimiterPtr limiter)
{
  FDK_ASSERT(limiter != NULL);
  return limiter->attack;
}

/* set number of channels */
TDLIMITER_ERROR setLimiterNChannels(TDLimiterPtr limiter, unsigned int nChannels)
{
  if ( limiter == NULL ) return TDLIMIT_INVALID_HANDLE;

if (nChannels > limiter->maxChannels) return TDLIMIT_INVALID_PARAMETER;

limiter->channels = nChannels;
  //resetLimiter(limiter);

return TDLIMIT_OK;
}

/* set sampling rate */
TDLIMITER_ERROR setLimiterSampleRate(TDLimiterPtr limiter, unsigned int sampleRate)
{
  unsigned int attack, release;
  FIXP_DBL attackConst, releaseConst, exponent;
  INT e_ans;

if ( limiter == NULL ) return TDLIMIT_INVALID_HANDLE;

if (sampleRate > limiter->maxSampleRate) return TDLIMIT_INVALID_PARAMETER;

/* update attack and release time in samples */
  attack = (unsigned int)(limiter->attackMs * sampleRate / 1000);
  release = (unsigned int)(limiter->releaseMs * sampleRate / 1000);

/* attackConst = pow(0.1, 1.0 / (attack + 1)) */
  exponent = invFixp(attack+1);
  attackConst = fPow(FL2FXCONST_DBL(0.1f), 0, exponent, 0, &e_ans);
  attackConst = scaleValue(attackConst, e_ans);

limiter->attack        = attack;
  limiter->attackConst   = attackConst;
  limiter->releaseConst  = releaseConst;
  limiter->sampleRate    = sampleRate;

/* reset */
  //resetLimiter(limiter);

return TDLIMIT_OK;
}

/* set attack time */
TDLIMITER_ERROR setLimiterAttack(TDLimiterPtr limiter, unsigned int attackMs)
{
  unsigned int attack;
  FIXP_DBL attackConst, exponent;
  INT e_ans;

if ( limiter == NULL ) return TDLIMIT_INVALID_HANDLE;

if (attackMs > limiter->maxAttackMs) return TDLIMIT_INVALID_PARAMETER;

/* calculate attack time in samples */
  attack = (unsigned int)(attackMs * limiter->sampleRate / 1000);

/* attackConst = pow(0.1, 1.0 / (attack + 1)) */
  exponent = invFixp(attack+1);
  attackConst = fPow(FL2FXCONST_DBL(0.1f), 0, exponent, 0, &e_ans);
  attackConst = scaleValue(attackConst, e_ans);

limiter->attack        = attack;
  limiter->attackConst   = attackConst;
  limiter->attackMs      = attackMs;

return TDLIMIT_OK;
}

/* set release time */
TDLIMITER_ERROR setLimiterRelease(TDLimiterPtr limiter, unsigned int releaseMs)
{
  unsigned int release;
  FIXP_DBL releaseConst, exponent;
  INT e_ans;

if ( limiter == NULL ) return TDLIMIT_INVALID_HANDLE;

/* calculate  release time in samples */
  release = (unsigned int)(releaseMs * limiter->sampleRate / 1000);

limiter->releaseConst  = releaseConst;
  limiter->releaseMs     = releaseMs;

return TDLIMIT_OK;
}

/* set limiter threshold */
TDLIMITER_ERROR setLimiterThreshold(TDLimiterPtr limiter, INT_PCM threshold)
{
  if ( limiter == NULL ) return TDLIMIT_INVALID_HANDLE;

limiter->threshold = (FIXP_PCM)threshold;

return TDLIMIT_OK;
}

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