[LAU] help with guitarix settings - jack issue

[Dominic Sacré]

On Sun, Mar 27, 2011 at 2:20 PM, Peder Hedlund <peder at musikhuset.org> wrote:
> Quoting Cedric Roux <sed at free.fr>:
>> ----- "Peder Hedlund" <peder at musikhuset.org> wrote:
>>> 3. Why are you using different soundcards for capture and playback?
>>
>> why not? I have an internal soundcard for playback
>> and an external usb device (ua1ex) for audio
>> capture. What's wrong with that?
>
> You're introducing additional complexity to the setup. You also seem to be
> running them at different bit depth (24 vs 32) which may or may not be a
> problem. Until you get things working, see if you can use the ualex for
> playback as well.

More importantly, you can only use two sound cards with JACK at the
same time if their sample clocks are synchronized. This can be
achieved with an S/PDIF connection between the two cards, but of
course that's only an option if both cards actually have digital
connectors.

Without synchronization the sound cards' sample clocks will drift,
which invariably leads to xruns. This is not JACK's fault by the way,
it's simply how the hardware works.
The only other solution to this is resampling, which is what alsa_in
and alsa_out do. But resampling will have some negative effect on
audio quality, so I would only use it as a last resort. Why exactly
don't you want to use the USB device for both capture and playback?


Dominic