Topic: Octamic XTC: USB Class mode

I just tested the Octamic XTC in USB audio/MIDI class compliant mode. Am I right that in USB class mode the XTC is always using 44.1 kHz? I tried this with several computers and iOS devices and as soon as the XTC was attached by USB cable, the clock displayed on the XTC LCD automatically switched to 44.1 kHz and at this point the XTC setup menu did not allow me to change the rate at all while the USB connection was still established.

So is that the expected behaviour of the XTC in USB Class mode or might it be a configuration issue on my side? I could not find any restrictions mentioned in the XTC user manual regarding the USB Class mode.


Re: Octamic XTC: USB Class mode

In macOS you entered the Audio MIDI Setup and changed the XTCs sample rate to something different?

For iOS you need apps that can change the sample rate, like Auria or Cubasis. Both is found in the manual:

Under Mac OS X two modes are available: 8/4 channels at up to 192 kHz, and 24/24 channels at up to 96 kHz, depending on what has been selected in Audio MIDI Setup.
In Class Compliant mode the default clock mode is Internal, and iOS typically sets 96 kHz. Any app can change / set the sample rate to a desired value, but not all apps include a choice to select one. Setting the OctaMic XTC (and with it the i-device) to slave mode by selecting the AES, ADAT or MADI input as clock source, the OctaMic XTC will be synchronized to the external digital sample rate. With a wrong external sample rate heavy audio noise will occur. Without an external signal the OctaMic XTC changes to its internal clock, with the sample rate set by iOS or the app in use.

Matthias Carstens

Re: Octamic XTC: USB Class mode

Ah, good to know that it is probably an issue on my side. Thanks!

Actually I was just experimenting with several OSs so far to check feasability, but the real intended idea was to misuse one of my XTCs in USB Class mode with a Linux machine. Because for a project, I have to create a digital audio & MIDI bridge (@96 kHz stereo) between a Mac and a Linux PC. So my idea was misusing two XTCs like this:

Linux PC --(USB)--> XTC(1) --(ADAT+WordClock)--> XTC(2) --(MADI)--> MADIFace USB --(USB)--> Mac

So I will try to change the sample rate with ALSA on Linux.

BTW I also tried the following more simple setup (for the same purpose described above) with only one XTC:

Linux PC --(USB)--> XTC --(MADI)--> MADIFace USB --(USB)--> Mac

But the MADI LED started flashing at the XTC and I got misbehaviours with TotalMix on the Mac. Not sure if the latter usage is outside the designed scope of the XTC or whether it was a clock rate conflict (i.e. single speed on XTC vs. quad speed assumed on Mac side).