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alsa: dynamically adjust the DLL bandwidth

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Keep a running average and variance of the error. Use this to
periodically update the DLL bandwidth. When the variance gets smaller,
we update the DLL more slowly to stay closer to the ideal rate.

This seems to improve the rate stability.
This commit is contained in:
Wim Taymans 2024-10-04 10:47:47 +02:00
parent d1efc9c2c6
commit 0db2171cd9
2 changed files with 17 additions and 5 deletions
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21
spa/plugins/alsa/alsa-pcm.c
View file

@ -2746,7 +2746,7 @@ static int get_status(struct state *state, uint64_t current_time, snd_pcm_uframe
static int update_time(struct state *state, uint64_t current_time, snd_pcm_sframes_t delay,
snd_pcm_sframes_t target, bool follower)
{
double err, corr;
double err, corr, avg;
int32_t diff;
if (state->disable_tsched && !follower) {
@ -2784,10 +2784,16 @@ static int update_time(struct state *state, uint64_t current_time, snd_pcm_sfram
err = -state->max_error;
}
if (!follower || state->matching)
if (!follower || state->matching) {
corr = spa_dll_update(&state->dll, err);
else
avg = (state->err_avg * state->err_wdw + (err - state->err_avg)) / (state->err_wdw + 1.0);
state->err_var = (state->err_var * state->err_wdw +
(err - state->err_avg) * (err - avg)) / (state->err_wdw + 1.0);
state->err_avg = avg;
} else {
corr = 1.0;
}
if (diff < 0)
state->next_time += (uint64_t)(diff / corr * 1e9 / state->rate);
@ -2796,10 +2802,14 @@ static int update_time(struct state *state, uint64_t current_time, snd_pcm_sfram
state->base_time = state->next_time;
spa_log_debug(state->log, "%s: follower:%d match:%d rate:%f "
"bw:%f thr:%u del:%ld target:%ld err:%f max:%f",
"bw:%f thr:%u del:%ld target:%ld err:%f max:%f var:%f:%f:%f",
state->name, follower, state->matching,
corr, state->dll.bw, state->threshold, delay, target,
err, state->max_error);
err, state->max_error, state->err_avg, state->err_var, state->err_wdw);
spa_dll_set_bw(&state->dll,
SPA_CLAMPD(sqrt(state->err_var)/1000.0, 0.001, SPA_DLL_BW_MAX),
state->threshold, state->rate);
}
if (state->rate_match) {
@ -2904,6 +2914,7 @@ static inline int check_position_config(struct state *state, bool starting)
state->threshold = SPA_SCALE32_UP(state->driver_duration, state->rate, state->driver_rate.denom);
state->max_error = SPA_MAX(256.0f, state->threshold / 2.0f);
state->max_resync = SPA_MIN(state->threshold, state->max_error);
state->err_wdw = (double)state->driver_rate.denom/state->driver_duration;
state->resample = !state->pitch_elem &&
(((uint32_t)state->rate != state->driver_rate.denom) || state->matching);
state->alsa_sync = true;