commit 770520886bcb0213f65aabd13cc48671826dab14
author Jean-Marc Valin <jmvalin@jmvalin.ca> Mon Jul 04 01:06:11 2016 -0400
committer Jean-Marc Valin <jmvalin@jmvalin.ca> Mon Jul 04 01:07:37 2016 -0400
tree e66d734da2a9112109b9fbf571f9415c961140ef
parent fdf0df42e4878d99c5a8f49a7826472e2e921e79

Adds some smoothing to the energy quantization

When the energy is stable, we slightly bias energy quantization towards
the previous error to make the gain more stable (a constant offset is
better than fluctuations).

We reduce the bitrate by about 0.2% to 1% at low bitrate for the same quality.

celt/celt_encoder.c

diff --git a/celt/celt_encoder.c b/celt/celt_encoder.c
index 1520a6c..1f6d0ce 100644
--- a/celt/celt_encoder.c
+++ b/celt/celt_encoder.c
@@ -124,6 +124,7 @@
    /* opus_val16 oldBandE[],     Size = channels*mode->nbEBands */
    /* opus_val16 oldLogE[],      Size = channels*mode->nbEBands */
    /* opus_val16 oldLogE2[],     Size = channels*mode->nbEBands */
+   /* opus_val16 energyError[],  Size = channels*mode->nbEBands */
 };
 
 int celt_encoder_get_size(int channels)
@@ -137,9 +138,10 @@
    int size = sizeof(struct CELTEncoder)
          + (channels*mode->overlap-1)*sizeof(celt_sig)    /* celt_sig in_mem[channels*mode->overlap]; */
          + channels*COMBFILTER_MAXPERIOD*sizeof(celt_sig) /* celt_sig prefilter_mem[channels*COMBFILTER_MAXPERIOD]; */
-         + 3*channels*mode->nbEBands*sizeof(opus_val16);  /* opus_val16 oldBandE[channels*mode->nbEBands]; */
+         + 4*channels*mode->nbEBands*sizeof(opus_val16);  /* opus_val16 oldBandE[channels*mode->nbEBands]; */
                                                           /* opus_val16 oldLogE[channels*mode->nbEBands]; */
                                                           /* opus_val16 oldLogE2[channels*mode->nbEBands]; */
+                                                          /* opus_val16 energyError[channels*mode->nbEBands]; */
    return size;
 }
 
@@ -1320,7 +1322,7 @@
    VARDECL(int, tf_res);
    VARDECL(unsigned char, collapse_masks);
    celt_sig *prefilter_mem;
-   opus_val16 *oldBandE, *oldLogE, *oldLogE2;
+   opus_val16 *oldBandE, *oldLogE, *oldLogE2, *energyError;
    int shortBlocks=0;
    int isTransient=0;
    const int CC = st->channels;
@@ -1400,6 +1402,7 @@
    oldBandE = (opus_val16*)(st->in_mem+CC*(overlap+COMBFILTER_MAXPERIOD));
    oldLogE = oldBandE + CC*nbEBands;
    oldLogE2 = oldLogE + CC*nbEBands;
+   energyError = oldLogE2 + CC*nbEBands;
 
    if (enc==NULL)
    {
@@ -1775,6 +1778,19 @@
    }
 
    ALLOC(error, C*nbEBands, opus_val16);
+   c=0;
+   do {
+      for (i=start;i<end;i++)
+      {
+         /* When the energy is stable, slightly bias energy quantization towards
+            the previous error to make the gain more stable (a constant offset is
+            better than fluctuations). */
+         if (ABS32(SUB32(bandLogE[i+c*nbEBands], oldBandE[i+c*nbEBands])) < QCONST16(2.f, DB_SHIFT))
+         {
+            bandLogE[i+c*nbEBands] -= MULT16_16_Q15(energyError[i+c*nbEBands], QCONST16(0.25f, 15));
+         }
+      }
+   } while (++c < C);
    quant_coarse_energy(mode, start, end, effEnd, bandLogE,
          oldBandE, total_bits, error, enc,
          C, LM, nbAvailableBytes, st->force_intra,
@@ -2074,6 +2090,14 @@
       ec_enc_bits(enc, anti_collapse_on, 1);
    }
    quant_energy_finalise(mode, start, end, oldBandE, error, fine_quant, fine_priority, nbCompressedBytes*8-ec_tell(enc), enc, C);
+   OPUS_CLEAR(energyError, nbEBands*CC);
+   c=0;
+   do {
+      for (i=start;i<end;i++)
+      {
+         energyError[i+c*nbEBands] = MAX16(-QCONST16(0.5f, 15), MIN16(QCONST16(0.5f, 15), error[i+c*nbEBands]));
+      }
+   } while (++c < C);
 
    if (silence)
    {

celt/quant_bands.c

diff --git a/celt/quant_bands.c b/celt/quant_bands.c
index 95076e0..46777b3 100644
--- a/celt/quant_bands.c
+++ b/celt/quant_bands.c
@@ -418,6 +418,7 @@
             offset = (q2-.5f)*(1<<(14-fine_quant[i]-1))*(1.f/16384);
 #endif
             oldEBands[i+c*m->nbEBands] += offset;
+            error[i+c*m->nbEBands] -= offset;
             bits_left--;
          } while (++c < C);
       }