On 3/20/16 2:24 PM, Georg Chini wrote:
On 20.03.2016 19:13, Alexander E. Patrakov wrote:
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.
why is a resampler needed when doing a loopback on the same card?
Hi Alexander,
no, I am working with speex-float-5. I just re-tested zitaj-bridge, and
I was wrong,
it shows the same behavior. I am also seeing double lines, so it is
probably deeper
down in the alsa driver.
I also tested your 318 ms - same result.
To rule out artifacts produced by the oscilloscope I fed the input
signal directly to the
second channel - this looks fine.
The choice of the resampler does no longer have any impact on the
performance
of module-loopback. For small latencies (70ms - 100ms) I can keep the
latency jitter
now well below 100 usec for HDA -> USB on my system, this corresponds to a
difference of 35 mm in hearing distance. When the USB device is run in
batch mode
the result is even better but less robust to changes in system load.
zitaj-bridge is still somewhat better for HDA -> USB and USB -> HDA (~50
usec)
but always fails after a few minutes complaining about excessive timing
errors
even for HDA -> HDA on the same card.
_______________________________________________
pulseaudio-discuss mailing list
pulseaudio-discuss@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/pulseaudio-discuss
_______________________________________________
pulseaudio-discuss mailing list
pulseaudio-discuss@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/pulseaudio-discuss
