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Improve band-limited synth

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Lior Halphon
2024-11-21 21:12:30 +02:00
parent ad2360b5c3
commit 7e071e463d
1 changed files with 10 additions and 6 deletions
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16
Core/apu.c
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@@ -12,21 +12,25 @@ static int32_t band_limited_steps[GB_BAND_LIMITED_PHASES][GB_BAND_LIMITED_WIDTH]
static void __attribute__((constructor)) band_limited_init(void) static void __attribute__((constructor)) band_limited_init(void)
{ {
const unsigned master_size = GB_BAND_LIMITED_WIDTH * GB_BAND_LIMITED_PHASES; const unsigned master_size = GB_BAND_LIMITED_WIDTH * GB_BAND_LIMITED_PHASES;
double *master = malloc(master_size * sizeof(*master)); double *master = malloc(master_size * sizeof(*master));
nounroll for (unsigned i = 0; i < master_size; i++) {
master[i] = 0.5;
}
const unsigned sine_size = 256 * GB_BAND_LIMITED_PHASES + 2; const unsigned sine_size = 256 * GB_BAND_LIMITED_PHASES + 2;
const unsigned max_harmonic = sine_size / 2 / GB_BAND_LIMITED_PHASES; const unsigned max_harmonic = sine_size / 2 / GB_BAND_LIMITED_PHASES;
nounroll for (unsigned harmonic = 1; harmonic <= max_harmonic; harmonic += 2) { nounroll for (unsigned harmonic = 1; harmonic <= max_harmonic; harmonic += 2) {
double amplitude = 4 / M_PI / harmonic / 2; double amplitude = 1.0 / harmonic / 2;
double to_angle = M_PI * 2 / sine_size * harmonic; double to_angle = M_PI * 2 / sine_size * harmonic;
nounroll for (unsigned i = 0; i < master_size; i++) { nounroll for (unsigned i = 0; i < master_size; i++) {
master[i] += sin(((signed)i - (signed)master_size / 2) * to_angle) * amplitude; master[i] += sin(((signed)(i + 1) - (signed)master_size / 2) * to_angle) * amplitude;
} }
} }
// Normalize master waveform
nounroll for (unsigned i = 0; i < master_size - 1; i++) {
master[i] += master[master_size - 1];
master[i] /= master[master_size - 1] * 2;
}
master[master_size - 1] = 1;
nounroll for (unsigned phase = 0; phase < GB_BAND_LIMITED_PHASES; phase++) { nounroll for (unsigned phase = 0; phase < GB_BAND_LIMITED_PHASES; phase++) {
int32_t error = GB_BAND_LIMITED_ONE; int32_t error = GB_BAND_LIMITED_ONE;
int32_t prev = 0; int32_t prev = 0;