(2nd attempt to post as the edit appeared to leave the thread completely blank.)
I saw the sticky for the Qu-series digital noise topic, but didn’t see an indication that this applied to the SQ-series as well, hence the separate topic.
The attached ogg mp3 file shows the result I have when connecting a PC application (Ardour 5.12.0) to the SQ-5 over the USB-B protocol. The majority of the time the audio is clean, but I’ll get the distortions that seem to be described for the Qu-series on the audio sent from the PC into the SQ-5. I am running the latest firmware on the mixer, 1.2.2. The issue can be heard at 5-8 seconds, and again at 13-18 seconds into the file.
The attached file was recorded by mapping the USB input channel to an Aux send routed as a mix back out the USB interface and recording it into another track in Ardour. This accurately reflects what I hear when monitoring the input channel directly from the mixer as well.
The PC in question runs Ubuntu 17.10, although I’ve experienced this same issue on my laptop with Ubuntu 16.04 as well (there using both USB 2 & USB 3 ports.) I’ve attached the detailed lsusb output for the SQ-5 as well, if it’s of any use; if additional information would help, feel free to inquire. CPU usage is low, and locking the CPU frequency governor to the chip’s max rated clock-rate have no effect.
The tree of the SQ-5 USB layout looks like this:
|__ Port 7: Dev 8, If 0, Class=(Defined at Interface level), Driver=, 480M
|__ Port 7: Dev 8, If 1, Class=Audio, Driver=snd-usb-audio, 480M
|__ Port 7: Dev 8, If 2, Class=Audio, Driver=snd-usb-audio, 480M
|__ Port 7: Dev 8, If 3, Class=Audio, Driver=snd-usb-audio, 480M
|__ Port 7: Dev 8, If 4, Class=Audio, Driver=snd-usb-audio, 480M
|__ Port 7: Dev 8, If 5, Class=Audio, Driver=snd-usb-audio, 480M
I’m wondering if this appears to be the same issue as on the Qu-series, or if this is something different. Suggestions as to a fix are welcome. While I can make other arrangements to feed audio from the PC into the mixer, it would be nice to have full support for USB mapping with clean audio.