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loopback: Adjust rate based on latency difference

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Replace the current latency controller with a modified P-controller. For
better readability separate the controller function. For small latency
differences, the controller forms a classical P-controller while it saturates
at 1% deviation from the base rate for large latency differences.
This commit is contained in:
Georg Chini 2016-06-05 21:05:10 +02:00 • committed by Tanu Kaskinen
parent 4a11742652
commit c03633766c
1 changed files with 30 additions and 20 deletions
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50
src/modules/module-loopback.c
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@ -168,11 +168,34 @@ static void teardown(struct userdata *u) {
}
}
/* rate controller
* - maximum deviation from base rate is less than 1%
* - can create audible artifacts by changing the rate too quickly
* - exhibits hunting with USB or Bluetooth sources
*/
static uint32_t rate_controller(
uint32_t base_rate,
pa_usec_t adjust_time,
int32_t latency_difference_usec) {
uint32_t new_rate;
double min_cycles;
/* Calculate best rate to correct the current latency offset, limit at
* slightly below 1% difference from base_rate */
min_cycles = (double)abs(latency_difference_usec) / adjust_time / 0.01 + 1;
new_rate = base_rate * (1.0 + (double)latency_difference_usec / min_cycles / adjust_time);
return new_rate;
}
/* Called from main context */
static void adjust_rates(struct userdata *u) {
size_t buffer, fs;
size_t buffer;
uint32_t old_rate, base_rate, new_rate;
int32_t latency_difference;
pa_usec_t current_buffer_latency, snapshot_delay, current_source_sink_latency, current_latency, latency_at_optimum_rate;
pa_usec_t final_latency;
pa_assert(u);
pa_assert_ctl_context();
@ -197,6 +220,9 @@ static void adjust_rates(struct userdata *u) {
/* Latency at base rate */
latency_at_optimum_rate = current_source_sink_latency + current_buffer_latency * old_rate / base_rate;
final_latency = u->latency;
latency_difference = (int32_t)((int64_t)latency_at_optimum_rate - final_latency);
pa_log_debug("Loopback overall latency is %0.2f ms + %0.2f ms + %0.2f ms = %0.2f ms",
(double) u->latency_snapshot.sink_latency / PA_USEC_PER_MSEC,
(double) current_buffer_latency / PA_USEC_PER_MSEC,
@ -209,26 +235,10 @@ static void adjust_rates(struct userdata *u) {
u->latency_snapshot.max_request*2,
u->latency_snapshot.min_memblockq_length);
fs = pa_frame_size(&u->sink_input->sample_spec);
if (u->latency_snapshot.min_memblockq_length < u->latency_snapshot.max_request*2)
new_rate = base_rate - (((u->latency_snapshot.max_request*2 - u->latency_snapshot.min_memblockq_length) / fs) *PA_USEC_PER_SEC)/u->adjust_time;
else
new_rate = base_rate + (((u->latency_snapshot.min_memblockq_length - u->latency_snapshot.max_request*2) / fs) *PA_USEC_PER_SEC)/u->adjust_time;
if (new_rate < (uint32_t) (base_rate*0.8) || new_rate > (uint32_t) (base_rate*1.25)) {
pa_log_warn("Sample rates too different, not adjusting (%u vs. %u).", base_rate, new_rate);
new_rate = base_rate;
} else {
if (base_rate < new_rate + 20 && new_rate < base_rate + 20)
new_rate = base_rate;
/* Do the adjustment in small steps; 2‰ can be considered inaudible */
if (new_rate < (uint32_t) (old_rate*0.998) || new_rate > (uint32_t) (old_rate*1.002)) {
pa_log_info("New rate of %u Hz not within 2‰ of %u Hz, forcing smaller adjustment", new_rate, old_rate);
new_rate = PA_CLAMP(new_rate, (uint32_t) (old_rate*0.998), (uint32_t) (old_rate*1.002));
}
}
/* Calculate new rate */
new_rate = rate_controller(base_rate, u->adjust_time, latency_difference);
/* Set rate */
pa_sink_input_set_rate(u->sink_input, new_rate);
pa_log_debug("[%s] Updated sampling rate to %lu Hz.", u->sink_input->sink->name, (unsigned long) new_rate);
}