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af_scaletempo: use taxicab distance for offset search

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Cross correlation is the defualt method for correlating signals in
signal processing, but in this case the taxicab distance gets better
results.
This commit is contained in:
Christoph Heinrich 2023-10-03 03:48:00 +02:00 committed by Kacper Michajłow
parent 3f6874f4d7
commit 18ed9e105a
1 changed files with 11 additions and 11 deletions
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22
audio/filter/af_scaletempo.c
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@ -2,7 +2,7 @@
* scaletempo audio filter
*
* scale tempo while maintaining pitch
* (WSOLA technique with cross correlation)
* (WSOLA technique with taxicab distance)
* inspired by SoundTouch library by Olli Parviainen
*
* basic algorithm
@ -136,19 +136,19 @@ static bool fill_queue(struct priv *s)
static int best_overlap_offset_float(struct priv *s)
{
float best_corr = INT_MIN;
float best_distance = FLT_MAX;
int best_off = 0;
float *search_start = (float *)s->buf_queue + s->num_channels;
for (int off = 0; off < s->frames_search; off++) {
float corr = 0;
float distance = 0;
float *ps = search_start;
float *po = s->buf_overlap;
po += s->num_channels;
for (int i = s->num_channels; i < s->samples_overlap; i++)
corr += *po++ * *ps++;
if (corr > best_corr) {
best_corr = corr;
distance += fabsf(*po++ - *ps++);
if (distance < best_distance) {
best_distance = distance;
best_off = off;
}
search_start += s->num_channels;
@ -159,19 +159,19 @@ static int best_overlap_offset_float(struct priv *s)
static int best_overlap_offset_s16(struct priv *s)
{
int64_t best_corr = INT64_MIN;
int32_t best_distance = INT32_MAX;
int best_off = 0;
int16_t *search_start = (int16_t *)s->buf_queue + s->num_channels;
for (int off = 0; off < s->frames_search; off++) {
int64_t corr = 0;
int32_t distance = 0;
int16_t *ps = search_start;
int16_t *po = s->buf_overlap;
po += s->num_channels;
for (int i = s->num_channels; i < s->samples_overlap; i++)
corr += *po++ * (int32_t)*ps++;
if (corr > best_corr) {
best_corr = corr;
distance += abs((int32_t)*po++ - (int32_t)*ps++);
if (distance < best_distance) {
best_distance = distance;
best_off = off;
}
search_start += s->num_channels;