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Adjust fine bits allocation.

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The old code allocated too many fine bits to large bands.
New allocations were derived from by numerical optimization using quantization
 MSE sampled from Laplacian distributed random data to within +/- 1 bit for
 N=2...160 and bits per band from 0 to 64.
Those allocations could be modeled with only minor errors using a simple offset
 of 19/8+log2(N), with no bits spent on fine energy when there would not be
 enough bits remaining to code a single pulse.
However, PEAQ testing suggested an offset of 14/8 was better, and that it was
 always worth spending at least one bit on fine energy.
This commit is contained in:
Timothy B. Terriberry 2010-07-27 07:49:24 -07:00 • committed by Jean-Marc Valin
parent 6f1cbca519
commit a345decd97
2 changed files with 4 additions and 2 deletions
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4
libcelt/rate.c
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@ -160,7 +160,7 @@ static inline void interp_bits2pulses(const CELTMode *m, int start, int end, int
N=M*(m->eBands[j+1]-m->eBands[j]);
/* Compensate for the extra DoF in stereo */
d=(C*N+ ((C==2 && N>2) ? 1 : 0))<<BITRES;
offset = FINE_OFFSET - m->logN[j] - logM;
offset = FINE_OFFSET - ((m->logN[j] + logM)>>1);
/* Offset for the number of fine bits compared to their "fair share" of total/N */
offset = bits[j]-offset*N*C;
/* Compensate for the prediction gain in stereo */
@ -173,6 +173,8 @@ static inline void interp_bits2pulses(const CELTMode *m, int start, int end, int
if (N==1)
ebits[j] = (bits[j]/C >> BITRES)-1;
if (ebits[j] < 1)
ebits[j] = 1;
/* Make sure not to bust */
if (C*ebits[j] > (bits[j]>>BITRES))
ebits[j] = bits[j]/C >> BITRES;

2
libcelt/rate.h
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@ -40,7 +40,7 @@
#define LOG_MAX_PULSES 7
#define BITRES 3
#define FINE_OFFSET 25
#define FINE_OFFSET 14
#define QTHETA_OFFSET 18
#define BITOVERFLOW 30000