I've misplaced my USB audio kit, but I'm reasonably sure I read from /dev/audio (and a cursory reading of the source suggests that ought to work). Is there any reason to do otherwise? I don't know what audioin is intended to buy. Given that it's never been in audio(3), I'm not sure it's important to support it.

It's unfortunate that volume and audioctl don't support the same language. Don't add another. It's pretty easy to handle both; see /sys/src/cmd/usb/audio/audiofs.c. The one for audioctl is reasonably regular and comprehensive; it'd be nice to standardize our audio interfaces around that.

I'm more interested in audiostat. I don't see that in the usb implementation, and I'm not clear on whether it could be provided there. Anyone know? Should audio programs treat that as optional?

"deprecation" in unix is a mess, where things can stay "deprecated" for ages. it'd be nice to be able to say "/dev/volume (or /dev/eia0status) was a mistake; here's a backwards-compatible improvement, and the old stuff goes away in 6 months."