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Limit rate adjustments to small, inaudible jumps

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The same logic is applied to the sample rate adjustments in module-rtp-recv,
module-loopback and module-combine:
 - Each time an adjustment is made, the new rate can differ at most 2‰ from the
   old rate.  Such a step is equal to 3.5 cents (a cent is 1/100th of a
   semitone) and as 5 cents is generally considered the smallest observable
   difference in pitch, this results in inaudible adjustments.
 - The sample rate of the stream can only differ from the rate of the
   corresponding sink by 25%.  As these adjustments are meant to account for
   very small clock drifts, any large deviation from the base rate suggests
   something is seriously wrong.
 - If the calculated rate is within 20Hz of the base rate, set it to the base
   rate.  This saves CPU because no resampling is necessary.
This commit is contained in:
Maarten Bosmans 2011-01-07 01:25:55 +01:00
parent 11dbe30bfa
commit 8b4cb54595
3 changed files with 51 additions and 25 deletions
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18
src/modules/module-loopback.c
View file

@ -175,13 +175,13 @@ static void adjust_rates(struct userdata *u) {
buffer_latency = pa_bytes_to_usec(buffer, &u->sink_input->sample_spec);
pa_log_info("Loopback overall latency is %0.2f ms + %0.2f ms + %0.2f ms = %0.2f ms",
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) buffer_latency / PA_USEC_PER_MSEC,
(double) u->latency_snapshot.source_latency / PA_USEC_PER_MSEC,
((double) u->latency_snapshot.sink_latency + buffer_latency + u->latency_snapshot.source_latency) / PA_USEC_PER_MSEC);
pa_log_info("Should buffer %zu bytes, buffered at minimum %zu bytes",
pa_log_debug("Should buffer %zu bytes, buffered at minimum %zu bytes",
u->latency_snapshot.max_request*2,
u->latency_snapshot.min_memblockq_length);
@ -194,9 +194,21 @@ static void adjust_rates(struct userdata *u) {
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;
pa_log_info("Old rate %lu Hz, new rate %lu Hz", (unsigned long) old_rate, (unsigned long) new_rate);
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));
}
}
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);
pa_core_rttime_restart(u->core, u->time_event, pa_rtclock_now() + u->adjust_time);
}