[FFmpeg-cvslog] avfilter/af_acrossover: improve quality for odd order butterworth
Paul B Mahol
git at videolan.org
Fri Nov 27 13:53:09 EET 2020
ffmpeg | branch: master | Paul B Mahol <onemda at gmail.com> | Fri Nov 27 12:42:58 2020 +0100| [1555cfedf6fab91ef86b4e85b872c2afa77c818f] | committer: Paul B Mahol
avfilter/af_acrossover: improve quality for odd order butterworth
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=1555cfedf6fab91ef86b4e85b872c2afa77c818f
---
libavfilter/af_acrossover.c | 45 +++++++++++++++++++++++++++++++++++++--------
1 file changed, 37 insertions(+), 8 deletions(-)
diff --git a/libavfilter/af_acrossover.c b/libavfilter/af_acrossover.c
index 4f0dbbcfb3..98bd6fe7a9 100644
--- a/libavfilter/af_acrossover.c
+++ b/libavfilter/af_acrossover.c
@@ -58,6 +58,8 @@ typedef struct AudioCrossoverContext {
int order;
int filter_count;
+ int first_order;
+ int ap_filter_count;
int nb_splits;
float *splits;
@@ -205,6 +207,18 @@ static void set_ap(BiquadContext *b, double fc, double q, double sr)
b->a2 = -a2 / a0;
}
+static void set_ap1(BiquadContext *b, double fc, double sr)
+{
+ double omega = M_PI * fc / sr;
+ double K = tan(omega);
+
+ b->a1 = -(1. - K) / (1. + K);
+ b->a2 = 0.;
+ b->b0 = -b->a1;
+ b->b1 = 1.;
+ b->b2 = 0.;
+}
+
static void calc_q_factors(int order, double *q)
{
double n = order / 2.;
@@ -218,7 +232,6 @@ static int config_input(AVFilterLink *inlink)
AVFilterContext *ctx = inlink->dst;
AudioCrossoverContext *s = ctx->priv;
int sample_rate = inlink->sample_rate;
- int first_order;
double q[16];
s->xover = av_calloc(inlink->channels, sizeof(*s->xover));
@@ -227,21 +240,29 @@ static int config_input(AVFilterLink *inlink)
s->order = (s->order_opt + 1) * 2;
s->filter_count = s->order / 2;
- first_order = s->filter_count & 1;
+ s->first_order = s->filter_count & 1;
+ s->ap_filter_count = s->filter_count / 2 + s->first_order;
calc_q_factors(s->order, q);
for (int ch = 0; ch < inlink->channels; ch++) {
for (int band = 0; band <= s->nb_splits; band++) {
- if (first_order) {
+ if (s->first_order) {
set_lp(&s->xover[ch].lp[band][0], s->splits[band], 0.5, sample_rate);
set_hp(&s->xover[ch].hp[band][0], s->splits[band], 0.5, sample_rate);
}
- for (int n = first_order; n < s->filter_count; n++) {
- const int idx = s->filter_count / 2 - ((n + first_order) / 2 - first_order) - 1;
+ for (int n = s->first_order; n < s->filter_count; n++) {
+ const int idx = s->filter_count / 2 - ((n + s->first_order) / 2 - s->first_order) - 1;
set_lp(&s->xover[ch].lp[band][n], s->splits[band], q[idx], sample_rate);
set_hp(&s->xover[ch].hp[band][n], s->splits[band], q[idx], sample_rate);
+ }
+
+ for (int x = 0; x <= s->nb_splits && s->first_order; x++)
+ set_ap1(&s->xover[ch].ap[x][band][0], s->splits[band], sample_rate);
+
+ for (int n = s->first_order; n < s->ap_filter_count; n++) {
+ const int idx = (s->filter_count / 2 - ((n * 2 + s->first_order) / 2 - s->first_order) - 1);
for (int x = 0; x <= s->nb_splits; x++)
set_ap(&s->xover[ch].ap[x][band][n], s->splits[band], q[idx], sample_rate);
@@ -340,17 +361,25 @@ static int filter_channels(AVFilterContext *ctx, void *arg, int jobnr, int nb_jo
}
for (int aband = band + 1; aband < ctx->nb_outputs; aband++) {
- for (int f = 0; f < s->filter_count / 2; f++) {
+ if (s->first_order) {
+ const double *src = (const double *)frames[band]->extended_data[ch];
+ double *dst = (double *)frames[band]->extended_data[ch];
+ BiquadContext *ap = &xover->ap[band][aband][0];
+
+ biquad_process(ap, dst, src, nb_samples);
+ }
+
+ for (int f = s->first_order; f < s->ap_filter_count; f++) {
const double *src = (const double *)frames[band]->extended_data[ch];
double *dst = (double *)frames[band]->extended_data[ch];
- BiquadContext *ap = &xover->ap[band][aband][f * 2 + (s->filter_count & 1)];
+ BiquadContext *ap = &xover->ap[band][aband][f];
biquad_process(ap, dst, src, nb_samples);
}
}
}
- for (int band = 0; band < ctx->nb_outputs && (s->filter_count & 1); band++) {
+ for (int band = 0; band < ctx->nb_outputs && s->first_order; band++) {
if (band & 1) {
double *dst = (double *)frames[band]->extended_data[ch];
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