Re: [Jack-Devel] extra latency compensation

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DateTue, 19 Apr 2011 21:58:07 -0500
From Chris Caudle <[hidden] at chriscaudle dot org>
To[hidden] at lists dot jackaudio dot org
Follow-UpClemens Ladisch Re: [Jack-Devel] extra latency compensation
On Tue, April 19, 2011 1:05 am, Clemens Ladisch wrote:
> In addition to the already mentioned USB queueing delay
> (up to 24 ms, depending on the period size)

Is that constant?  If so, it should get calibrated out by using the
jack_iodelay measurements, right?

> USB also adds a somewhat random delay
> between the playback and capture streams.

That is disappointing.
Why have I not run across this information before?  I would have thought
that a lot of musicians would have been complaining about random time
offsets when overdubbing.
Or is it +/-1ms worst case?  If that is the limit, then probably it is not
noticeable in most cases.  If the delay stays constant once the stream is
started, I think it should be roughly equivalent to moving a microphone 1
ft/0.3m farther away from an acoustic instrument, and I think no one would
complain about that.

> all these latencies can be explained by known deficiencies
> in the Linux USB stack.

The general USB stack used by all applications, or specifically the USB
audio device support?  Is the deficiency something that can be corrected
in ALSA code, or would have to be addressed in the general USB support in
the Linux kernel?

Maybe this is all much ado about nothing.  I think I'll just lay down some
drum tracks on a night when I haven't had beer and see if it matters. 
Maybe close is good enough.

-- 
Chris Caudle
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