[LAU] Testing JACK and PA latency

Hartmut Noack zettberlin at linuxuse.de
Thu Sep 19 09:19:53 UTC 2013

Am 19.09.2013 10:46, schrieb Patrick Shirkey:
> Moving this thread to LAU as it seems to be a more generic issue now:
> I am testing the round trip latency when using PA and JACK together. I
> have the following connection graph:
> jack_system (in) -> pa_source (in) -> audacity (in) -> audacity (out) ->
> pa sink (out) -> jack_system (out)

Unless your research is completely academic I do not see a practical use
for its results on the user-side. For Audacity latency is not a big
issue. It does not build for realtime-application rather for offline
editing, audio-restauration etc, in that field a latency of 100ms is
still OK....

> Audacity is run in pass through mode with internal latency set to 0.
> I would like to measure the round trip latency from jack_system (in) to
> jack_system (out)
> This is a slightly unusual request but it is actually a reasonably
> important measurement in the bigger scheme of things.
> Does anyone have any suggestions?
> Ideally I would like to get accurate measurements for both input and
> output latency.
> input:
> jack_system (in) -> pa_source (in) -> audacity (in)
> output:
> audacity (out) -> pa sink (out) -> jack_system (out)
> So a tool that allowed me to measure the latency between every node on the
> graph would be perfect.
> Obviously made alot harder by mixing PA and JACK together. I have tried
> jack_iodelay but it does not measure the input signal from the mic instead
> it provides it's own signal.
> I suppose I could modify jack_iodelay to accept an input signal as the
> starting point for the latency graph but I have not looked into the code
> yet to see how tricky that would be.
> --
> Patrick Shirkey
> Boost Hardware Ltd
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> Linux-audio-user at lists.linuxaudio.org
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