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Variable bitrate experiment

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Mark Qvist 2015-04-24 10:47:50 +02:00
parent 095a558fcb
commit 8d9da446a4
2 changed files with 44 additions and 7 deletions
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25
hardware/AFSK.c
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@ -331,11 +331,32 @@ void AFSK_adc_isr(Afsk *afsk, int8_t currentSample) {
// to "smooth out" the variations in the samples.
afsk->iirX[0] = afsk->iirX[1];
afsk->iirX[1] = ((int8_t)fifo_pop(&afsk->delayFifo) * currentSample) >> 2;
#if FILTER_CUTOFF == 600
afsk->iirX[1] = ((int8_t)fifo_pop(&afsk->delayFifo) * currentSample) >> 2;
// The above is a simplification of:
// afsk->iirX[1] = ((int8_t)fifo_pop(&afsk->delayFifo) * currentSample) / 3.558147322;
#elif FILTER_CUTOFF == 800
afsk->iirX[1] = ((int8_t)fifo_pop(&afsk->delayFifo) * currentSample) >> 2;
// The above is a simplification of:
// afsk->iirX[1] = ((int8_t)fifo_pop(&afsk->delayFifo) * currentSample) / 2.899043379;
#else
#error Unsupported bitrate!
#endif
afsk->iirY[0] = afsk->iirY[1];
afsk->iirY[1] = afsk->iirX[0] + afsk->iirX[1] + (afsk->iirY[0] >> 1); // Chebyshev filter
#if FILTER_CUTOFF == 600
afsk->iirY[1] = afsk->iirX[0] + afsk->iirX[1] + (afsk->iirY[0] >> 1);
// The above is a simplification of a first-order 600Hz chebyshev filter:
// afsk->iirY[1] = afsk->iirX[0] + afsk->iirX[1] + (afsk->iirY[0] * 0.4379097269);
#elif FILTER_CUTOFF == 800
afsk->iirY[1] = afsk->iirX[0] + afsk->iirX[1] + (afsk->iirY[0] / 3);
// The above is a simplification of a first-order 800Hz chebyshev filter:
// afsk->iirY[1] = afsk->iirX[0] + afsk->iirX[1] + (afsk->iirY[0] * 0.3101172565);
#else
#error Unsupported bitrate!
#endif
// We put the sampled bit in a delay-line: