Channel hopping and signal modulation with MOTU UltraLite AVB

[Fritz Menzer]

Hello,

We've got a MOTU UltraLite AVB and are trying to get it to work properly with Ubuntu 20 as a class-compliant USB 2.0 device. However, when sound is played to the device, the channel associations switch in regular intervals. For example when you play a stereo signal, the sound may appear on the device in the "From Computer" channels 1/2 as expected, but sometimes it's 17/18 or 9/10 (the jump is always by a multiple of 8 channels).

Also, sometimes the sound appears in two pairs of channels, and that's when even weirder things happen. It's as if the signal gets modulated by a harmonic signal with a fundamental frequency of 8 kHz, so when I play a sweep signal, I see multiple copies of the sweep every 8 kHz, including aliased versions.

Is this a known bug for devices with many channels (the UltraLite AVB exposes 24 channels over its USB interface)? Will this ever be resolved?

There seems to be some interaction between the device's firmware and the ALSA driver, as earlier versions of the UltraLite AVB were reported to work with Linux, and after some changes in the hard- and firmware, it was not working with Linux anymore (see https://www.amazon.com/gp/customer-reviews/R1QF3JXJHUPDX1/ref=cm_cr_getr_d_rvw_ttl).

Best regards,

Fritz

[retnev]

I also want to know why this happens suddenly. Also happens to my Motu gear