[chuck-users] Issues when using several inputs on Motu Ultralite/OSX setup

Stefan Blixt stefan.blixt at gmail.com
Sun Dec 21 17:07:02 EST 2008

I made a thread about this issue here:
http://electro-music.com/forum/viewtopic.php?t=31032 . Kassen suggested that
I send an email here, thinking that this might require some insight
into RTAudio
(not sure myself what it is).
My Motu Ultralite runs ChucK applications perfectly, as long as I don't
bother configuring audio channels, making do with having sound output only
coming at the main outputs, and sound input from the MacBook Pro's built-in
input or microphone. The problems start when I try to route to other outputs
or want to use the Ultralite's inputs.

After a bit of trial-and-error, I managed to get ChucK to do what I want to
do (more or less) by using this command line to start the program:

chuck  --adc4 --in8 --out8 test.ck

Here's the test code I have been using:

adc.chan(6) => dac.chan(0);
adc.chan(7) => dac.chan(1);

while (true) {
        1::day => now;

This will route audio from inputs 7 and 8 to outputs 1 and 2 (not the main
outputs - if I want to hear the sound from the ChucK app I need to
physically connect the 1 and 2 output to another input on the sound

A curious thing here is that if I start like this instead:

chuck --adc4 --in8 --out6 test.ck // 6 outputs instead of 8

I get a mangled sound (sounding a bit like a sample rate or bandwidth
mismatch - check the sound sample that I attached at the
electro-music.comthread), and rather than just coming out of outputs 1
and 2 (as they do when
I use the previous command line), the sound appears at all eight analog
outputs on the Ultralite (according to the hardware meters on the Motu). If
I try --out4 I get sound on outputs 1,2,,5,6,7, and 8.

Another thing: if I leave out the output option altogether (i.e. take away
"--out8"), I get a mangled sound as before, but only on the main output.

I've also seen stuff like getting sound on every second output (1,3,5,7) for
some option, though I can't seem to reproduce that now.

I think I can work with what happens on my first example, but I'm still a
bit curious as to what is going on with these options, and why --out6 causes
the sound to behave radically different from --out8. I've checked my drivers
- the Ultralite firmware is up to date and I think the OSX drivers are too.
I'm running ChucK I might have to leave my Motu for a week, so i
might not be able to test stuff right away, if anyone comes up with


Release me, insect, or I will destroy the Cosmos!
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