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synthio: implement FIR filtering

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A 37-tap filter worked fine on RP2040 (prop maker) at 48kHz, so
you can probably pretty much go nuts on M7.
This commit is contained in:
Jeff Epler 2023-05-11 18:42:18 -05:00
parent f52bb65da6
commit bc7feb30a5
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GPG Key ID: D5BF15AB975AB4DE
1 changed files with 59 additions and 9 deletions
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68
shared-module/synthio/__init__.c
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@ -192,7 +192,7 @@ static void synth_note_into_buffer(synthio_synth_t *synth, int chan, int32_t *ou
uint32_t dds_rate;
const int16_t *waveform = synth->waveform_bufinfo.buf;
uint32_t waveform_length = synth->waveform_bufinfo.len / 2;
uint32_t waveform_length = synth->waveform_bufinfo.len / sizeof(int16_t);
uint32_t ring_dds_rate = 0;
const int16_t *ring_waveform = NULL;
@ -213,15 +213,15 @@ static void synth_note_into_buffer(synthio_synth_t *synth, int chan, int32_t *ou
int32_t frequency_scaled = synthio_note_step(note, sample_rate, dur, loudness);
if (note->waveform_buf.buf) {
waveform = note->waveform_buf.buf;
waveform_length = note->waveform_buf.len / 2;
waveform_length = note->waveform_buf.len / sizeof(int16_t);
}
dds_rate = synthio_frequency_convert_scaled_to_dds((uint64_t)frequency_scaled * waveform_length, sample_rate);
if (note->ring_frequency_scaled != 0 && note->ring_waveform_buf.buf) {
ring_waveform = note->ring_waveform_buf.buf;
ring_waveform_length = note->ring_waveform_buf.len / 2;
ring_waveform_length = note->ring_waveform_buf.len / sizeof(int16_t);
ring_dds_rate = synthio_frequency_convert_scaled_to_dds((uint64_t)note->ring_frequency_scaled * ring_waveform_length, sample_rate);
uint32_t lim = ring_waveform_length << SYNTHIO_FREQUENCY_SHIFT;
if (ring_dds_rate > lim / 2) {
if (ring_dds_rate > lim / sizeof(int16_t)) {
ring_dds_rate = 0; // can't ring at that frequency
}
}
@ -309,6 +309,37 @@ static void synth_note_into_buffer(synthio_synth_t *synth, int chan, int32_t *ou
}
}
STATIC void run_fir(synthio_synth_t *synth, int32_t *out_buffer32, uint16_t dur) {
int16_t *coeff = (int16_t *)synth->filter_bufinfo.buf;
size_t fir_len = synth->filter_bufinfo.len / sizeof(int16_t);
int32_t *in_buf = synth->filter_buffer;
// FIR and copy values to output buffer
for (int16_t i = 0; i < dur; i++) {
int32_t acc = 0;
for (size_t j = 0; j < fir_len; j++) {
// shift 5 here is good for up to 32 filtered voices, else might wrap
acc = acc + (in_buf[j] * (coeff[j] >> 5));
}
*out_buffer32++ = acc >> 10;
in_buf++;
}
// Move values down so that they get filtered next time
memmove(synth->filter_buffer, &synth->filter_buffer[dur], fir_len * sizeof(int32_t));
}
STATIC bool synthio_synth_get_note_filtered(mp_obj_t note_obj) {
if (note_obj == mp_const_none) {
return false;
}
if (!mp_obj_is_small_int(note_obj)) {
synthio_note_obj_t *note = MP_OBJ_TO_PTR(note_obj);
return note->filter;
}
return true;
}
void synthio_synth_synthesize(synthio_synth_t *synth, uint8_t **bufptr, uint32_t *buffer_length, uint8_t channel) {
if (channel == synth->other_channel) {
@ -326,11 +357,30 @@ void synthio_synth_synthesize(synthio_synth_t *synth, uint8_t **bufptr, uint32_t
int32_t out_buffer32[dur * synth->channel_count];
memset(out_buffer32, 0, sizeof(out_buffer32));
for (int chan = 0; chan < CIRCUITPY_SYNTHIO_MAX_CHANNELS; chan++) {
synth_note_into_buffer(synth, chan, out_buffer32, dur);
if (synth->filter_buffer) {
int32_t *filter_start = &synth->filter_buffer[synth->filter_bufinfo.len * synth->channel_count / sizeof(int16_t)];
memset(filter_start, 0, dur * sizeof(int32_t));
for (int chan = 0; chan < CIRCUITPY_SYNTHIO_MAX_CHANNELS; chan++) {
mp_obj_t note_obj = synth->span.note_obj[chan];
if (!synthio_synth_get_note_filtered(note_obj)) {
continue;
}
synth_note_into_buffer(synth, chan, filter_start, dur);
}
run_fir(synth, out_buffer32, dur);
} else {
memset(out_buffer32, 0, sizeof(out_buffer32));
}
for (int chan = 0; chan < CIRCUITPY_SYNTHIO_MAX_CHANNELS; chan++) {
mp_obj_t note_obj = synth->span.note_obj[chan];
if (synth->filter_buffer && synthio_synth_get_note_filtered(note_obj)) {
continue;
}
synth_note_into_buffer(synth, chan, out_buffer32, dur);
}
int16_t *out_buffer16 = (int16_t *)(void *)synth->buffers[synth->buffer_index];
@ -387,7 +437,7 @@ void synthio_synth_init(synthio_synth_t *synth, uint32_t sample_rate, int channe
synth->buffers[0] = m_malloc(synth->buffer_length, false);
synth->buffers[1] = m_malloc(synth->buffer_length, false);
if (synth->filter_bufinfo.len) {
synth->filter_buffer_length = (synth->filter_bufinfo.len + SYNTHIO_MAX_DUR) * channel_count * sizeof(int32_t);
synth->filter_buffer_length = (synth->filter_bufinfo.len / 2 + SYNTHIO_MAX_DUR) * channel_count * sizeof(int32_t);
synth->filter_buffer = m_malloc(synth->filter_buffer_length, false);
}
synth->channel_count = channel_count;
@ -419,7 +469,7 @@ STATIC void parse_common(mp_buffer_info_t *bufinfo, mp_obj_t o, int16_t what, mp
if (bufinfo->typecode != 'h') {
mp_raise_ValueError_varg(translate("%q must be array of type 'h'"), what);
}
mp_arg_validate_length_range(bufinfo->len / 2, 2, max_len, what);
mp_arg_validate_length_range(bufinfo->len / sizeof(int16_t), 2, max_len, what);
}
}