[LAU] Testing JACK and PA latency

Patrick Shirkey pshirkey at boosthardware.com
Fri Sep 20 18:07:32 UTC 2013

On Sat, September 21, 2013 1:12 am, Fons Adriaensen wrote:
> On Fri, Sep 20, 2013 at 08:41:10PM +1000, Patrick Shirkey wrote:
>> On Fri, September 20, 2013 8:31 pm, Fons Adriaensen wrote:
>> > On Fri, Sep 20, 2013 at 06:59:06PM +1000, Patrick Shirkey wrote:
>> >
>> >>  33114.906 frames    689.894 ms total roundtrip latency
>> >> 	extra loopback latency: 32922 frames
>> >> 	use 16461 for the backend arguments -I and -O ??
>> >
>> > Note the '??', it means the measurement is not reliable,
>> > probably due to skipped cycles (i.e. phase discontinuity).
>> >
>> xruns?
> Assuming you're measuring a 'clean' channel, the ?? most probably
> mean a discontinuity in the signal seen by jack_delay. In the
> sense that part of signal was 'jumped over' - a short gap that
> preserves the timing would not have any effect. This happens
> when Jack skips one or more cycles, and this in turn can be
> the result of an xrun (also of other things, but not in this
> case). Is your Jack running RT ?

I can hear the signal fine but I cannot hear or see the result of the
signal after it comes back in the mic input. I could attempt to capture
that part of the signal too for reference sake.

If there are significant dropouts will that be the likely cause of the "??"

I'm running jack with realtime capabilities but not a realtime kernel.
It's just a standard debian install at this point.

If anyone else has a fully tuned system that they know can do low latency
with jack and can provide test results for jack+pa that would be very

Patrick Shirkey
Boost Hardware Ltd

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