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

On Wed, Apr 13, 2011 at 11:57 PM, Chris Caudle <[hidden]> wrote:

> It also brings up a question of digital interfaces.  If I use the digital
> out from the card with external ADC and DAC, that is additional latency
> that the card has no way to know about. Is there anyway to tell JACK (or
> Ardour) about the additional latency so that it can be automatically
> compensated like it is when the analog interfaces of the card are used?

Same as with any card: you create a *physical* loopback from an output
to an input, and then use jdelay, or (with the most recent releases of
JACK) jack_iodelay (same program, different name) to measure the
"unreported" latency involved in the loopback routing. The output from
the program is not tremendously obvious in terms of how to use it.

To get a useful value, multiple frames/period by the periods/buffer
value. Subtract this from the number shown by jack_iodelay. Divide by
two.
Then give this value to the JACK backend with the -I and -O flags,
which specify "system input latency" and "system output latency".

--p

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