[Ardour-Dev] zita-a2j and capture alignment

Fons Adriaensen fons at linuxaudio.org
Tue Sep 10 06:19:01 PDT 2013

On Tue, Sep 10, 2013 at 09:12:27AM -0400, Paul Davis wrote:

> On Tue, Sep 10, 2013 at 9:05 AM, Fons Adriaensen <fons at linuxaudio.org>wrote:

> > Suppose you have two identical sound cards. One is used by Jack's backend,
> > the other by zita-a2j. Both set the correct capture latency value on their
> > ports. For a2j this will of course be a higher value than for the backend.
> >
> > Connect the same signal to the two cards, record two tracks simultaneously,
> > one from each card.
> >
> > I'd expect the two resulting regions
> >
> > * to be in sync when played back,
> > * to have different start/end points.
> >
> > assuming ardour uses the capture latency values to offset the regions.
> >
> > If not, how are the latency values used ?
> >
> in general, ardour's transport control for recording uses worst case
> numbers, not per-track numbers (we do not have per-track transport
> position). so we will keep recording for long enough to catch the last
> incoming data after the stop-recording request was noted, which may result
> in less/more data being captured in some tracks compared to others that
> started "late" because their own latency varied.

In the scenario above, should the two tracks be in sync, assuming the
latency values are correct but different ?



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