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audio: phase_vocoder: re-anchor synthesis phase on speed change #11058

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audio: phase_vocoder: re-anchor synthesis phase on speed change #11058

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27 changes: 27 additions & 0 deletions src/audio/phase_vocoder/phase_vocoder_common.c
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Original file line number Diff line number Diff line change
Expand Up @@ -215,6 +215,12 @@ static int32_t unwrap_angle_q27(int32_t angle)
void phase_vocoder_reset_for_new_speed(struct phase_vocoder_comp_data *cd)
{
struct phase_vocoder_state *state = &cd->state;
struct phase_vocoder_polar *polar = &state->polar;
struct phase_vocoder_fft *fft = &state->fft;
struct ipolar32 *polar_prev_ch;
int32_t *angle_delta_prev_ch;
int32_t *output_phase_ch;
int ch, i;

state->speed = cd->speed_ctrl;

Expand All @@ -232,6 +238,27 @@ void phase_vocoder_reset_for_new_speed(struct phase_vocoder_comp_data *cd)
*/
state->num_input_fft = 1;
state->num_output_ifft = 0;

/* Re-anchor synthesis phase so the first post-reset IFFT lands
* output_phase back on polar_prev.angle (the steady-state invariant).
* Between speed changes output_phase advances by one analysis-hop
* delta per output IFFT regardless of speed, so at speed != 1 it
* drifts away from the true polar angle; and each reset also adds
* one extra angle_delta_prev on the first no-consume IFFT. If not done,
* both accumulate across with interactive speed changes as a per-bin
* phase offset which smears transients and dulls the sound.
Comment on lines +247 to +249
*/
for (ch = 0; ch < cd->process_channels; ch++) {
polar_prev_ch = polar->polar_prev[ch];
angle_delta_prev_ch = polar->angle_delta_prev[ch];
output_phase_ch = polar->output_phase[ch];
if (!polar_prev_ch || !angle_delta_prev_ch || !output_phase_ch)
continue;

for (i = 0; i < fft->half_fft_size; i++)
output_phase_ch[i] =
unwrap_angle_q27(polar_prev_ch[i].angle - angle_delta_prev_ch[i]);
}
}

static void copy_polar_angles(int32_t *angle_delta_ch, struct ipolar32 *polar_data_ch,
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