Re: [LAU] Testing JACK and PA latency

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To: <linux-audio-user@...>
Date: Thursday, September 19, 2013 - 10:46 am

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

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.

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),

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.

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)

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Messages in current thread:
[LAU] Testing JACK and PA latency, Patrick Shirkey, (Thu Sep 19, 8:46 am)
Re: [LAU] Testing JACK and PA latency, Fons Adriaensen, (Thu Sep 19, 9:42 am)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Thu Sep 19, 10:04 am)
Re: [LAU] Testing JACK and PA latency, Fons Adriaensen, (Thu Sep 19, 10:46 am)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Wed Sep 25, 1:32 pm)
Re: [LAU] Testing JACK and PA latency, Len Ovens, (Thu Sep 19, 2:01 pm)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Thu Sep 19, 2:21 pm)
Re: [LAU] Testing JACK and PA latency, Len Ovens, (Thu Sep 19, 11:48 pm)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Fri Sep 20, 12:57 am)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Fri Sep 20, 8:59 am)
Re: [LAU] Testing JACK and PA latency, Fons Adriaensen, (Fri Sep 20, 10:31 am)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Fri Sep 20, 10:41 am)
Re: [LAU] Testing JACK and PA latency, Fons Adriaensen, (Fri Sep 20, 3:13 pm)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Fri Sep 20, 6:07 pm)
Re: [LAU] Testing JACK and PA latency, Fons Adriaensen, (Fri Sep 20, 7:08 pm)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Sat Sep 21, 11:27 am)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Thu Sep 19, 3:40 pm)
Re: [LAU] Testing JACK and PA latency, Fons Adriaensen, (Thu Sep 19, 12:31 pm)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Thu Sep 19, 12:35 pm)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Thu Sep 19, 10:26 am)
Re: [LAU] Testing JACK and PA latency, Hartmut Noack, (Thu Sep 19, 9:20 am)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Thu Sep 19, 9:39 am)
Re: [LAU] Testing JACK and PA latency, Len Ovens, (Thu Sep 19, 1:49 pm)
Re: [LAU] Testing JACK and PA latency, Patrick Shirkey, (Thu Sep 19, 2:04 pm)