Increased Gain + Hiss + Tapping Noise On Re-enabling Disabled Input

[specialmonkey]

I'm getting familiar with a 624 and its routing using the device's web page app. Using Win 10 / USB3. I may be able to setup a Thunderbolt card soon.

I have some very basic routing going on and during "quick setup" set it up to be an an audio interface only (vs audio interface + mixer, standalone mixer, etc).

I've paired it down to just 4 channels for "from" and "to" computer, and set mixer channels and AVB streams to 0.

I noticed that while I have Ableton Live Lite 10 up and running, I can speak into a mic (mic 1), play my guitar (guitar 1), or keyboard (analog 1/2), and it works. I can monitor all via my monitors or headphones in Ableton with monitoring set to Auto or In. The signals sound good.

While Ableton is up and running and I'm monitoring, if I decide I want to disable the mic or keyboard via the MOTU's web page routing app, and then I decide I'd like to re-enable it - all while actively monitoring in Ableton - upon re-enabling - there will be a massive gain increase, hiss, distortion and a faint tapping noise. Turning monitoring from Auto to off in Ableton shuts the harsh signal off (can't do it fast enough, the sound is unsettling!), but on re-enabling monitoring by selecting Auto again, no sound at all is available.

I must restart Ableton to get back to a good signal. Starting a new set/project without restarting does not resolve.

It struck me that it's probably bad workflow to change MOTU's device ins/outs (or to enable/disable them), etc. or change routing while actively monitoring/recording... or maybe it isn't?

I tried just enabling what I needed first, and setting the ins/outs in the routing grid prior to opening Ableton, and things seem to work fine. If I need to turn off a channel I can do that in the DAW.

I'm still wondering if this could be an issue with my new 624? MOTU thought it might be a hardware issue (not sure which hardware?) and asked me to try it on a different computer (which I cannot easily do). They said the issue hasn't been reported by anyone else as far as they know. Has anyone else experienced this? Maybe it's explainable, maybe I'm doing something ill advised? I am just getting familiar with the device.

Thanks for any info!

[specialmonkey]

I spoke to a MOTU support person who said he'd seen similar issues. He thought it could be a Windows audio issue. A possible alternate solution in lieu of restarting Ableton was changing the safety offset value in the MOTU Pro Audio Driver, temporarily, then changing it back. Having the routing in place before doing DAW work was also recommended.

[HCMarkus]

Thanks for sharing the info you developed; it may assist others.