[LAU] Testing JACK and PA latency
pshirkey at boosthardware.com
Thu Sep 19 09:39:00 UTC 2013
On Thu, September 19, 2013 7:19 pm, Hartmut Noack wrote:
> 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.
This is entirely professionally motivated and will also have major
benefits to academia too. I'm seeking suggestion on how to go about it not
arguments for why or if this is a useful thing to do... ;-)
> For Audacity latency is not a big
You can replace audacity with *any* application that can provide (near) 0
internal latency and full duplex pass through.
> It does not build for realtime-application rather for offline
> editing, audio-restauration etc, in that field a latency of 100ms is
> still OK....
In this case I have a hard limit of 20ms round trip latency from mic in to
speaker out and I would like to test the combination of JACK and PA to
determine where or if there are bottlenecks in the signal flow.
>> 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
>> 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
>> 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
>> Linux-audio-user mailing list
>> Linux-audio-user at lists.linuxaudio.org
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> Linux-audio-user at lists.linuxaudio.org
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