[Jack-Devel] is this latency coming from ALSA, jack, or ardour?

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DateMon, 11 Apr 2011 22:18:22 -0500
From Chris Caudle <[hidden] at chriscaudle dot org>
To[hidden] at lists dot jackaudio dot org
Follow-UpGeoff Beasley Re: [Jack-Devel] is this latency coming from ALSA, jack, or ardour?
Follow-UpNedko Arnaudov Re: [Jack-Devel] is this latency coming from ALSA, jack, or ardour?
I wanted to test out the new and better latency reporting in current jack,
so I made a session in Ardour 3 Alpha 4, turned on the click track and
then made the following three sessions:

jack 1.9.6, click track routed to track 1. Stopped transport, armed track 2
turned off click, routed track 1 to track 2. Stopped transport, armed track 3
routed track 2 to track 3. stopped transport, armed track 4,
etc.

So all internal jack routing, no audio interface involved.  As expected,
track 10 lined up perfectly with track 1.

So then I used my USB audio interface (Lexicon Lambda) with Alpha 4 and
jack 1.9.6.  By the time I got to track 10 with bounces, there was over 1
second of difference between track 1 and track 10.  Not really usable for
anything with lots of bounces.

I deleted all the jack 1.9.6 files, compiled and installed jack 2 from svn
(jackmp revision 4293), and did the same thing.  Now the click to track 1
offset is around 13ms, and the track 1 to track 9 offset is about 103 ms. 
I had the levels set too low, so I couldn't really see the onset of attack
by track 10 well enough to measure, but I assume bouncing to track 10
would add about 13ms more, just like the original click to track 1 bounce.

Is that as good as I can expect with a USB interface, or is jack 0.120
better than that?
I have a PCI interface available, so should I try that to compare against
the USB interface?  It took me about an hour to do this much, so it would
be tomorrow night before I could get back to it.  Just wondering whether
it is a useful exercise at all, and if it might be, which would be the
more useful info, jack2 SVN compared to jack 0.120, or USB interface
compared to PCI interface both using jack2 SVN.  Now that I think about
it, I suppose comparing the PCI to the USB would at least show whether the
interface was just reporting an incorrect latency value, which would
exonerate jack2 from the problem and point to ALSA if the same bounce test
worked with the PCI card.

Thoughts?

-- 
Chris Caudle
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