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switch to 16.16 fixed point for synthesis

This commit is contained in:
Jeff Epler 2023-04-01 11:42:51 -05:00
parent e9e4ce9546
commit e728a0c1b9
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GPG Key ID: D5BF15AB975AB4DE
1 changed files with 14 additions and 9 deletions
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23
shared-module/synthio/MidiTrack.c
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@ -94,9 +94,7 @@ void common_hal_synthio_miditrack_construct(synthio_miditrack_obj_t *self,
*self->track = initial;
self->waveform = waveform;
self->waveform_length = waveform_length;
(void)mp_arg_validate_length_min(waveform_length, 2, MP_QSTR_waveform);
mp_printf(&mp_plat_print, "note: waveform_length = %d\n", waveform_length);
mp_printf(&mp_plat_print, "waveform[0:2] = %d %d\n", waveform[0], waveform[1]);
mp_arg_validate_length_range(waveform_length, 2, 1024, MP_QSTR_waveform);
uint16_t dur = 0;
uint32_t pos = 0;
@ -217,7 +215,7 @@ audioio_get_buffer_result_t synthio_miditrack_get_buffer(synthio_miditrack_obj_t
int32_t sample_rate = self->sample_rate;
int active_channels = count_active_channels(&span);
const int16_t *waveform = self->waveform;
int16_t waveform_length = self->waveform_length;
uint32_t waveform_length = self->waveform_length;
int16_t *out_buffer = self->buffer;
if (active_channels) {
int16_t loudness = 0x3fff / (1 + active_channels);
@ -229,13 +227,20 @@ audioio_get_buffer_result_t synthio_miditrack_get_buffer(synthio_miditrack_obj_t
uint8_t octave = span.note[chan] / 12;
uint16_t base_freq = notes[span.note[chan] % 12];
uint32_t accum = self->accum[chan];
uint32_t rate = base_freq * waveform_length;
#define SHIFT (16)
// rate = base_freq * waveform_length
// den = sample_rate * 2 ^ (10 - octave)
// den = sample_rate * 2 ^ 10 / 2^octave
// dds_rate = 2^SHIFT * rate / den
// dds_rate = 2^(SHIFT-10+octave) * base_freq * waveform_length / sample_rate
uint32_t dds_rate = (sample_rate / 2 + ((uint64_t)(base_freq * waveform_length) << (SHIFT - 10 + octave))) / sample_rate;
for (uint16_t i = 0; i < dur; i++) {
accum += rate;
int16_t idx = ((accum / sample_rate) >> (10 - octave)) % waveform_length;
if (chan == 0 && i < 10) {
mp_printf(&mp_plat_print, "%d %d %d\n", accum, idx, waveform[idx]);
accum += dds_rate;
if (accum > waveform_length << SHIFT) {
accum -= waveform_length << SHIFT;
}
int16_t idx = accum >> SHIFT;
out_buffer[i] += (waveform[idx] * loudness) / 65536;
}
self->accum[chan] = accum;