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Change qb cap to prevent side-fold collapses.

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Previously, in a stereo split with itheta==16384, but without
 enough bits left over to actually code a pulse, the target band
 would completely collapse, because the mid gain would be zero and
 we don't fold the side.
This changes the limit to ensure that we never set qn>1 unless we
 know we'll have enough bits for at least one pulse.
This should eliminate the last possible whole-band collapse.
This commit is contained in:
Timothy B. Terriberry 2011-01-28 22:20:59 -08:00 • committed by Jean-Marc Valin
parent 17cab431db
commit 9b34bd835c
1 changed files with 10 additions and 5 deletions
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15
libcelt/bands.c
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@ -594,7 +594,7 @@ void haar1(celt_norm *X, int N0, int stride)
}
}
static int compute_qn(int N, int b, int offset, int stereo)
static int compute_qn(int N, int b, int offset, int pulse_cap, int stereo)
{
static const celt_int16 exp2_table8[8] =
{16384, 17866, 19483, 21247, 23170, 25267, 27554, 30048};
@ -602,9 +602,12 @@ static int compute_qn(int N, int b, int offset, int stereo)
int N2 = 2*N-1;
if (stereo && N==2)
N2--;
qb = IMIN((b>>1)-(1<<BITRES), (b+N2*offset)/N2);
/* The upper limit ensures that in a stereo split with itheta==16384, we'll
always have enough bits left over to code at least one pulse in the
side; otherwise it would collapse, since it doesn't get folded. */
qb = IMIN(b-pulse_cap-(4<<BITRES), (b+N2*offset)/N2);
qb = IMAX(0, IMIN(8<<BITRES, qb));
qb = IMIN(8<<BITRES, qb);
if (qb<(1<<BITRES>>1)) {
qn = 1;
@ -748,13 +751,15 @@ static unsigned quant_band(int encode, const CELTMode *m, int i, celt_norm *X, c
int itheta=0;
int mbits, sbits, delta;
int qalloc;
int pulse_cap;
int offset;
int orig_fill;
celt_int32 tell;
/* Decide on the resolution to give to the split parameter theta */
offset = ((m->logN[i]+(LM<<BITRES))>>1) - (stereo ? QTHETA_OFFSET_STEREO : QTHETA_OFFSET);
qn = compute_qn(N, b, offset, stereo);
pulse_cap = m->logN[i]+(LM<<BITRES);
offset = (pulse_cap>>1) - (stereo ? QTHETA_OFFSET_STEREO : QTHETA_OFFSET);
qn = compute_qn(N, b, offset, pulse_cap, stereo);
if (stereo && i>=intensity)
qn = 1;
if (encode)