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Using a noise-based PLC for the CELT layer in hybrid mode

--- a/celt/celt.c

+++ b/celt/celt.c

@@ -2007,8 +2007,7 @@

    celt_sig *overlap_mem[2];

    opus_val16 *lpc;

    opus_val32 *out_syn[2];

-   opus_val16 *oldBandE, *oldLogE2, *backgroundLogE;

-   int plc=1;

+   opus_val16 *oldBandE, *oldLogE, *oldLogE2, *backgroundLogE;

    SAVE_STACK;

    c=0; do {

@@ -2018,8 +2017,9 @@

    } while (++c<C);

    lpc = (opus_val16*)(st->_decode_mem+(DECODE_BUFFER_SIZE+st->overlap)*C);

    oldBandE = lpc+C*LPC_ORDER;

-   oldLogE2 = oldBandE + C*st->mode->nbEBands;

-   backgroundLogE = oldLogE2  + C*st->mode->nbEBands;

+   oldLogE = oldBandE + 2*st->mode->nbEBands;

+   oldLogE2 = oldLogE + 2*st->mode->nbEBands;

+   backgroundLogE = oldLogE2  + 2*st->mode->nbEBands;

    out_syn[0] = out_mem[0]+MAX_PERIOD-N;

    if (C==2)

@@ -2027,8 +2027,9 @@

    len = N+st->mode->overlap;

-   if (st->loss_count >= 5)

+   if (st->loss_count >= 5 || st->start!=0)

    {

+      /* Noise-based PLC/CNG */

       VARDECL(celt_sig, freq);

       VARDECL(celt_norm, X);

       VARDECL(celt_ener, bandE);

@@ -2043,14 +2044,24 @@

       ALLOC(X, C*N, celt_norm);   /**< Interleaved normalised MDCTs */

       ALLOC(bandE, st->mode->nbEBands*C, celt_ener);

-      log2Amp(st->mode, st->start, st->end, bandE, backgroundLogE, C);

-

+      if (st->loss_count >= 5)

+         log2Amp(st->mode, st->start, st->end, bandE, backgroundLogE, C);

+      else {

+         /* Energy decay */

+         opus_val16 decay = st->loss_count==0 ? QCONST16(1.5f, DB_SHIFT) : QCONST16(.5f, DB_SHIFT);

+         c=0; do

+         {

+            for (i=st->start;i<st->end;i++)

+               oldBandE[c*st->mode->nbEBands+i] -= decay;

+         } while (++c<C);

+         log2Amp(st->mode, st->start, st->end, bandE, oldBandE, C);

+      }

       seed = st->rng;

       for (c=0;c<C;c++)

       {

          for (i=0;i<(st->mode->eBands[st->start]<<LM);i++)

             X[c*N+i] = 0;

-         for (i=0;i<st->mode->effEBands;i++)

+         for (i=st->start;i<st->mode->effEBands;i++)

          {

             int j;

             int boffs;

@@ -2083,26 +2094,25 @@

             freq[c*N+i] = 0;

       } while (++c<C);

       compute_inv_mdcts(st->mode, 0, freq, out_syn, overlap_mem, C, LM);

-      plc = 0;

-   } else if (st->loss_count == 0)

-   {

-      opus_val16 pitch_buf[DECODE_BUFFER_SIZE>>1];

-      /* Corresponds to a min pitch of 67 Hz. It's possible to save CPU in this

-         search by using only part of the decode buffer */

-      int poffset = 720;

-      pitch_downsample(decode_mem, pitch_buf, DECODE_BUFFER_SIZE, C);

-      /* Max pitch is 100 samples (480 Hz) */

-      pitch_search(pitch_buf+((poffset)>>1), pitch_buf, DECODE_BUFFER_SIZE-poffset,

-            poffset-100, &pitch_index);

-      pitch_index = poffset-pitch_index;

-      st->last_pitch_index = pitch_index;

    } else {

-      pitch_index = st->last_pitch_index;

-      fade = QCONST16(.8f,15);

-   }

+      /* Pitch-based PLC */

+      if (st->loss_count == 0)

+      {

+         opus_val16 pitch_buf[DECODE_BUFFER_SIZE>>1];

+         /* Corresponds to a min pitch of 67 Hz. It's possible to save CPU in this

+         search by using only part of the decode buffer */

+         int poffset = 720;

+         pitch_downsample(decode_mem, pitch_buf, DECODE_BUFFER_SIZE, C);

+         /* Max pitch is 100 samples (480 Hz) */

+         pitch_search(pitch_buf+((poffset)>>1), pitch_buf, DECODE_BUFFER_SIZE-poffset,

+               poffset-100, &pitch_index);

+         pitch_index = poffset-pitch_index;

+         st->last_pitch_index = pitch_index;

+      } else {

+         pitch_index = st->last_pitch_index;

+         fade = QCONST16(.8f,15);

+      }

-   if (plc)

-   {

       c=0; do {

          VARDECL(opus_val32, e);

          opus_val16 exc[MAX_PERIOD];

@@ -2298,7 +2308,7 @@

       overlap_mem[c] = decode_mem[c]+DECODE_BUFFER_SIZE;

    } while (++c<CC);

    lpc = (opus_val16*)(st->_decode_mem+(DECODE_BUFFER_SIZE+st->overlap)*CC);

-   oldBandE = lpc+LPC_ORDER;

+   oldBandE = lpc+CC*LPC_ORDER;

    oldLogE = oldBandE + 2*st->mode->nbEBands;

    oldLogE2 = oldLogE + 2*st->mode->nbEBands;

    backgroundLogE = oldLogE2  + 2*st->mode->nbEBands;

--- a/celt/quant_bands.c

+++ b/celt/quant_bands.c

@@ -540,7 +540,7 @@

 }

 void log2Amp(const CELTMode *m, int start, int end,

-      celt_ener *eBands, opus_val16 *oldEBands, int _C)

+      celt_ener *eBands, const opus_val16 *oldEBands, int _C)

 {

    int c, i;

    const int C = CHANNELS(_C);

--- a/celt/quant_bands.h

+++ b/celt/quant_bands.h

@@ -39,7 +39,7 @@

       celt_ener *bandE, opus_val16 *bandLogE, int _C);

 void log2Amp(const CELTMode *m, int start, int end,

-      celt_ener *eBands, opus_val16 *oldEBands, int _C);

+      celt_ener *eBands, const opus_val16 *oldEBands, int _C);

 void quant_coarse_energy(const CELTMode *m, int start, int end, int effEnd,

       const opus_val16 *eBands, opus_val16 *oldEBands, opus_uint32 budget,