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avfilter/af_acrossover: improve quality for odd order butterworth

This commit is contained in:
Paul B Mahol 2020-11-27 12:42:58 +01:00
parent 3864896017
commit 1555cfedf6
1 changed files with 37 additions and 8 deletions
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45
libavfilter/af_acrossover.c
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@ -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][f * 2 + (s->filter_count & 1)];
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];
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];