[LAD] Routing signals in mixer (Ardour, Qtractor)

[Rui Nuno Capela]

On 07/12/2010 07:27 PM, Louigi Verona wrote:
> Okay, last message for today.
> 
> Eventually I could partially reproduce. If I create a stereo Vocoder
> track FIRST, then the latter mono carrier and modifier tracks would
> channel into Vocoder provided I press "monitor" on it. But the output is
> a weird mix of vocoded signal and the modifier. If I change modifier and
> carrier places - the signal does not change. Why would track creation
> matter I do not know. Rui?
> 
> Also, when Vocoder does not receive anything, it starts to generate
> XRUNs, so if you close Qtractor while Vocoder is activated, Qtractor
> will freeze.
> 
> All in all, I am puzzled why Jeremy could do it, but not me. I hope I am
> just missing a simple detail.
> 

aha, you are :)

in short, qtractor internal process flow doesn't play well with direct
feedback loops, like connecting any of its output ports to any of its
own input ports.

problem is that input buffers are always read before any output signal
is produced, while on the same process period cycle. iow, you're
consuming what hasn't been produced yet. that's why you'll probably get
silence, at best.

problem, if you call it that way, can be solved artificially by
inserting an "all-pass" jack client in between qtractor outs and ins. of
course this will introduce an inevitable period latency. but its the
only way to workaround the issue.

i'm afraid Jeremy did present an interesting proof-of-concept exercise
re. using the ladspa vocoder in qtractor. afaics, he didn't said it was
of any use, let alone practical :)

cheers
-- 
rncbc aka Rui Nuno Capela
rncbc at rncbc.org