[LAU] MotU Ultralite AVB observations.

[Fernando Lopez-Lezcano]

On 3/7/20 1:52 PM, John Murphy wrote:
> On Sat, 7 Mar 2020 12:28:26 +0000 John Murphy wrote:
> 
> [...]
>> I can only think that my dual booting and using it on Windows 10
>> caused the trouble I was seeing when using it on Linux afterwards.
> 
> I seem to have narrowed it down to dependence on the setting of
> 'Clock Mode'. I do a lot of recordings from a 48kHz optical source
> plugged into the S/Pdiff optical input. Seems to be that clock the
> kernel can't use. Probably because it has somehow changed the device
> to 44.1kHz (via 192kHz) and then demands a 44.1kHz clock.
> 
> If I set Clock Mode to internal, before booting Linux, or after
> a failed start up, I see fewer 'clock source 1 is not valid'
> messages in /var/log/syslog and jackd will work as usual. I've
> even had sound in my (FireFox) browser, so Alsa must be working.
> 
> If I don't set Clock Mode to internal, /var/log/syslog gets the
> full compliment of 6 blocks of 40 'not valid' messages, ending
> with: [pulseaudio] module-udev-detect.c: Tried to configure
> /devices/pci0000:00/0000:00:14.0/usb1/1-14/1-14:1.0/sound/card2
> (alsa_card.usb-MOTU_UltraLite_AVB_0001f2fffe005ded-00) more often
> than 5 times in 10s.
> 
> It had to be something like that.. Was doing my ed in a bit.
> 
> Big clue to the problem right there in the device's LCD display.
> If the sample rate indicator keeps flashing - it isn't going to work.

When the sampling rate changes in the Motu audio interface, it takes 
some time (4-10 seconds) for the new sampling rate to "lock" (indicator 
flashing).

During that time jack will not successfully start. It is a pain.

There is an amixer control that can be used to query the interface and 
see if the sampling rate is locked or not.

This is further complicated by the fact that some software (ie: 
pulseaudio) will change the sampling rate without you doing it manually. 
For example, if you manage to start jackd at 48Khz and then stop it, 
pulseaudio (if installed and enabled) will take control of the audio 
interface and change the sampling rate to its default rate (44.1k).

-- Fernando