[pulseaudio-discuss] [PATCH 09/13] loopback: Track the amount of jitter

[Alexander E. Patrakov]

09.12.2015 01:47, Tanu Kaskinen пишет:
> On Wed, 2015-02-25 at 19:43 +0100, Georg Chini wrote:
>> ---
>>   src/modules/module-loopback.c | 18 +++++++++++++++++-
>>   1 file changed, 17 insertions(+), 1 deletion(-)
>
> The commit message should say something about why the jitter is tracked.
>
>> diff --git a/src/modules/module-loopback.c b/src/modules/module-loopback.c
>> index cbd0ac9..b733663 100644
>> --- a/src/modules/module-loopback.c
>> +++ b/src/modules/module-loopback.c
>> @@ -95,6 +95,8 @@ struct userdata {
>>
>>       pa_usec_t source_latency_sum;
>>       pa_usec_t sink_latency_sum;
>> +    pa_usec_t next_latency;
>> +    double latency_error;
>>
>>       bool in_pop;
>>       bool pop_called;
>> @@ -263,15 +265,22 @@ static void adjust_rates(struct userdata *u) {
>>                   (double) current_latency / PA_USEC_PER_MSEC,
>>                   (double) corrected_latency / PA_USEC_PER_MSEC,
>>                   ((double) u->latency_snapshot.sink_latency + current_buffer_latency + u->latency_snapshot.source_latency) / PA_USEC_PER_MSEC);
>> -    pa_log_debug("Latency difference: %0.2f ms, rate difference: %i Hz",
>> +    pa_log_debug("Latency difference: %0.2f ± %0.2f ms, rate difference: %i Hz",
>
> What does "± %0.2f ms" mean? Is the real latency difference between
> those bounds with 100% confidence, or less than 100% confidence?

Of course less than 100% confidence.

>
>>                   (double) latency_difference / PA_USEC_PER_MSEC,
>> +                (double) 2.5 * u->latency_error * final_latency / PA_USEC_PER_MSEC,
>
> Why is that 2.5 there?

Maybe it would be more scientific to track not the "average of absolute 
value of jitter", but some "root-mean-square" value. Then we can use the 
two-sigma or two-and-a-half-sigma rule to get 95% or 98% confidence that 
the latency is within the bounds that we log.

-- 
Alexander E. Patrakov