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

[Georg Chini]

On 08.12.2015 21:47, Tanu Kaskinen wrote:
> 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.

OK

>> 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?

This is just an indication of the current error (with respect to the model),
so not 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?
>

Good question. I think it was copied over from the definition of the 
deadband in the next
patch. The observed errors are however in good agreement with that factor.