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
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