19 Sep
2013
19 Sep
'13
12:46 p.m.
On Thu, Sep 19, 2013 at 08:04:04PM +1000, Patrick Shirkey wrote:
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).
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.
If they are a single Jack client you create a loop in Jack's
processing graph, this adds one period to the measurement.
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)
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? 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 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? 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?