[Jack-Devel] jack vs. motu (usb)

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Tue Oct 25 21:49:44 CEST 2016

Hi all!,

Has anyone seen this and hopefully found a workaround?

To make a long story short, it takes a Motu card of the new generation 
(24ao, 1248, etc) about 6 seconds to change the sampling rate (!). That 
happens when switching from one sampling rate to another, and also after 
first connecting the card to a Linux system over USB (Fedora 23).

When Jack is started for the first time after changing sampling rate, or 
right after the card is plugged into the system, it probably asks the 
ALSA driver "can this card do this sampling rate with these other 
parameters?" and the answer is "yes", but when actually setting it it 
apparently fails and jack does not start.

Now, if after that you slowly count to 7 (just to be safe) and try to 
start Jack again, it just works (I presume the card has already finished 
switching sampling rates in the background while you wait, and 
everything is fine).

When using aplay to help debug this it turns out that aplay does not 
complain, and it happily plays the soundfile, but nothing comes out of 
the speakers for the first few seconds - I presume until the card 
switches sampling rate.

Once the sampling rate has been defined at least _once_ then Jack has no 
problem to start (over and over again) and aplay plays files with sound 
from the beginning.

If you access the status and configuration web server in the Motu you 
can switch the sampling rate and you see the clock lock icon turn 
blinking red and then solid white once the change is done. Also, 
alsamixer and amixer show a single read only "control" that is actually 
the lock status indicator (the lsusb descriptors also show another r/w 
control that can be used to _set_ the frequency but that is somehow not 
reflected in the alsamixer/amixer interface).

Suggestions? Patches? :-)
-- Fernando

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