On Thu, Sep 19, 2013 at 08:04:04PM +1000, Patrick Shirkey wrote: > > 1. Measure the round-trip latency of your sound card (with an > > external analog loop). > > > > Can I use jack_delay running on a second computer connected to the > external i/o of the first computer to get this value? You'd measure something different... But you could use two computers as follows: A = computer with jack, PA, audacity B = second computer with sound card, jack and jack_delay. 1. Measure the round-trip latency on B, with an external analog loop. 2. Connect B -> A, A -> B, run complete chain on A. 3. Measure again on B, subtract the value from (1). > > jack_delay -> pa_source -> audacity -> pa_sink -> jack_delay. > > > > Does this look reasonable? > > 1023.978 frames 21.333 ms total roundtrip latency > extra loopback latency: 1023 frames > use 511 for the backend arguments -I and -O > 1023.976 frames 21.333 ms total roundtrip latency > extra loopback latency: 1023 frames > use 511 for the backend arguments -I and -O > 1023.977 frames 21.333 ms total roundtrip latency > extra loopback latency: 1023 frames > use 511 for the backend arguments -I and -O Don't know - I'm by no means a PA expert... and I don't know your Jack period size. Given PA's reputation I'd expect more: 1024 samples would mean that PA imposes almost the same RT- requirements on apps as Jack does, and it was designed *not* to do that... But maybe the jack <-> PA interface doesn't use the same amount of buffering that PA normally adds. Note that the value measured is modulo 2^16 samples, but I wouldn't expect anything more than a second, so this probably irrelevant. > > 3. If pa_source and pa_sink are a single Jack client (probably not), > > subtract one period from the result of (2). > > Can you explain that with the data above? If they are a single Jack client you create a loop in Jack's processing graph, this adds one period to the measurement. > > 4. Add the two values. > > > > I would like to provide an app for this task. Do you think it would be > worthwhile to extend jack_iodelay for this purpose? Don't see how. You need to do two measurements anyway, no matter how it's done, then add or substract. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
