Latest 10.11 beta, I've discovered that USB Audio degrades over time to really rough with a lot of drops. Unplugging and reattaching the device clears the problem for a while, but then it goes ****** again.
USB Audio
Issues with some USB 2.0 peripherals attached by USB are a known bug:
"Known Issues
USB storage devices, including internal SD card readers, may become unavailable after system sleep and require either re-plug or restart to recover.
USB 1.0, 1.1 and older 2.0 devices may not function"
(from: https://developer.apple.com/library/prerelease/mac/releasenotes/General/rn-osx-10.11/index.html)
USB Audio drops sporadically in latest Beta. Unplugging and re-plugging reastores for a while.