[LAU] Make mno mic input be both in L an R channels

Niels Mayer nielsmayer at gmail.com
Sun Jun 20 19:52:02 UTC 2010


I have a question about a different way of doing this (soundcard mixer
dependent), and whether it is advantageous (or not) to use a soundcard's
built-in mixer, e.g. for direct monitoring at low-latency. If you have a
soundcard like the Terratec DMX6Fire or the M-Audio Delta66 you certainly
have the capability for this.
If you have a supported soundcard, from "alsa-tools" you use , e.g.
:/usr/bin/cspctl , /usr/bin/echomixer , /usr/bin/envy24control
, /usr/bin/hdspconf , /usr/bin/hdspmixer/ , /usr/bin/rmedigicontrol
, /usr/bin/sscape_ctl , /usr/bin/us428control ...

The alternative is to route via jack using qjackctl and/or take care of
mixing/monitoring in the DAW, e.g. ardour/rosegarden/qtractor.

What are the advantages of using the soundcard's digital mixer, esp.
envy24control & snd_ice1712
to route a single sound-source to an output for auditioning; or, if mixing
is needed, use the built-in digital mixer to directly mix the different
sound-sources? Note you have the option of digital-sync to a source that can
be mixed back through the digital mixer's SPDIF inputs as well (e.g.
reverb/room effects, madonna's-vocal-backing-track). And then route the
digital mix as the "headphone mix" back to the performer.

The main advantage I would predict (and can see) is slightly lower CPU
usage, which might matter on a laptop or older computer, but just seems like
a trivial amount of extra processing on today's fast 4 core machines. The
other advantage would be latency -- I can see no way that routing in and out
of soundcard(s) through jack would not add some latency -- the hardware
mixing option is marketed as "0 latency monitoring" for a reason.

However, in-practice, this practice is bedevilled by the mains or headphone
monitor outputs automatically being routed back from the digital mixer L/R
outputs, to their PCM0-3 outputs: at least when used via Jack/qjackctl . So
eventually, you end up hearing silence (since I usually would then digital
mix PCM4-7 leaving PCM0-3 unused or silent for this scenario). Any
suggestions, help or workarounds on the latter would be appreciated as well.
As I have yet to characterise what causes the automatic-routing-switchover,
(sometimes it can happen after a few hours, other times after a few minutes)

Niels
http://nielsmayer.com
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