[pulseaudio-discuss] Latency problem with long latencies

[Alexander E. Patrakov]

20.03.2016 22:41, Georg Chini пишет:
> Hello,
>
> I am still working on module-loopback and hit a problem that I cannot
> explain.
> When running a HDA card with long latency (333ms) I see that the resulting
> latency is not stable but varies around 300 usec. What is worse, the
> changes
> in latency are not even reported, module-loopback sees a completely stable
> value ( +/-10 usec).
> My setup: I have a bitscope dual channel USB oscilloscope attached to
> another
> machine. This device also has a function generator that I set to 1kHz
> rectangle.
> The signal is input to the HDA card and fed to the output of the same
> card via
> module-loopback. Input and output signal are measured using the
> oscilloscope.
> The movement of the edge of the output signal now shows the "latency
> jitter"
> which can be made visible by using the overlay mode of the oscilloscope.
>
> The result for HDA (module-loopback running with 500ms adjust time and 1s
> latency) is shown at http://georg.chini.tk/hda_333ms_3.png. Some of the
> original
> input signal is somehow fed into the output signal, don't know where
> this happens,
> so please ignore it as it has no impact on the result.

No idea either, just some blind pokes...

1. Are you using the trivial resampler? Does anything change if you 
change the resampler type?
2. Do you get the same trace with a "weird" latency (not something that 
can be derived from one second by multiplication or division by small 
factors)? E.g. something like 318 ms.

To me, it looks like something is sometimes creating an 
off-by-one-sample error when copying the data. Which is exactly the job 
of the trivial resampler, that's why the question.

-- 
Alexander E. Patrakov