[LAU] Testing JACK and PA latency

Patrick Shirkey pshirkey at boosthardware.com
Thu Sep 19 08:46:11 UTC 2013

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)

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.

jack_system (in) -> pa_source (in) -> audacity (in)

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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