I found a workaround to this problem that I and others have been experiencing with USB interfaces not coming back to life correctly after stopping jack. The symptoms are distorted, quiet, and crackly audio after stopping jack. I don't fully know the cause. I suspect the interface isn't reverting to the correct sample rate somehow when jack stops. I had been unplugging the USB cable and plugging it back in to reset it which fixed it just fine but puts extra wear and tear on my hardware. I just found the usbreset utility though.
For my card I do the following:
- Enter "usbreset" in a terminal and find your interface in the list.
- Use "sudo usbreset" and whichever of the methods listed in the terminal referring to your device you prefer.
- In my case I used "sudo usbreset 001/004" because that is the location shown for my card in the terminal.
I wish there was a way to do it without sudo but alas.
Hope that's helpful,
Robin Cherry