// derive capture scaling factor from peak value in current buffer
// this gives more interesting captures for display.
int32_t shift = 32;
- for (size_t i = 0; i < inBuffer->frameCount; i++) {
+ int len = inBuffer->frameCount * 2;
+ for (size_t i = 0; i < len; i++) {
int32_t smp = inBuffer->s16[i];
- if (smp < 0) smp = -smp;
+ if (smp < 0) smp = -smp - 1; // take care to keep the max negative in range
int32_t clz = __builtin_clz(smp);
if (shift > clz) shift = clz;
}
- // never scale by less than 8 to avoid returning unaltered PCM signal.
- // add one to combine the division by 2 needed after summing left and right channels below
- if (20 > shift) {
- shift = (31 - 8 + 1) - shift;
- } else {
- shift = (3 + 1);
+ // A maximum amplitude signal will have 17 leading zeros, which we want to
+ // translate to a shift of 8 (for converting 16 bit to 8 bit)
+ shift = 25 - shift;
+ // Never scale by less than 8 to avoid returning unaltered PCM signal.
+ if (shift < 3) {
+ shift = 3;
}
+ // add one to combine the division by 2 needed after summing left and right channels below
+ shift++;
uint32_t captIdx;
uint32_t inIdx;
inIdx < inBuffer->frameCount && captIdx < pContext->mCaptureSize;
inIdx++, captIdx++) {
int32_t smp = inBuffer->s16[2 * inIdx] + inBuffer->s16[2 * inIdx + 1];
- smp = (smp + (1 << (shift - 1))) >> shift;
+ smp = smp >> shift;
buf[captIdx] = ((uint8_t)smp)^0x80;
}
pContext->mCaptureIdx = captIdx;