Re: [LAD] Looping audio to oneself via Jack

Excerpts from Fred Gleason's message of 2011-05-04 00:20:33 +0200:
> Howdy Folks:
>
> Here's a seemingly trivial requirement that has me stymied: I have a Jack client (external, built against 0.102.20) where it occasionally makes sense to connect an output port to an input on the same client. QJackCtl happily makes the connection; the process callback delivers data as expected, but it's all zeros for the connected input port! I can route the same client output port to a physical output (ALSA backend) and hear the expected audio. Likewise, a physical capture port connected to the input on the client receives data from the card as expected. It's only the "loopback" within the same client that doesn't want to go.
>
> At first I suspected that the JackPortIsTerminal flag might have some bearing on this, but changing this value seems to have no effect. Am I missing something blatantly obvious here, or is this something that is just not within the scope of Jack to allow?
>
> Any pointers greatly appreciated.
>
> Cheers!
>
> |-------------------------------------------------------------------------|
> | Frederick F. Gleason, Jr. | Chief Developer |
> | | Paravel Systems |
> |-------------------------------------------------------------------------|
> | ...one of the main causes of the fall of the Roman Empire was that, |
> | lacking zero, they had no way to indicate successful termination of |
> | their C programs. |
> | -- Robert Firth |
> |-------------------------------------------------------------------------|

I can't tell you about jack API stuff that might be relevant but I can
tell you that it usually works, there's nothing in jack that forbids it.
There's one thing though you should be aware of: the output will reach
the input one processing cycle after the output was produced, hence it
will be delayed. This is simply a consequence of how jack works.

Regards,
Philipp

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Received on Wed May 4 12:15:02 2011