USB host mode with class compliant audio interfaces
I think USB Audio support was initially built into Android 4.0 ICS but there may be earlier implementations and not every hardware that supports USB OTG and runs ICS+ supports USB Audio.

The capability of an Android device to handle USB audio mainly depends on the Kernel running on your System and your hardware being able to handle USB devices (USB host). Custom kernel and ROMs can void this. I have been able to connect (to my stock Samsung Galaxy Note 2):


an Alesis I/O4 USB Soundcard from Alesis (4in, 4out, phantom power)
a Harman/Kardon v1 USB speaker system and
a Shure x2u soundcard (1in, 2out, phantom power)


all playing stereo (Alesis could not be configured to play on all four channels) and the soundcards also record (alesis recording 4 tracks in sync) in very nice quality. I used Urecord (mono/ stereo) and USB Audio Recorder PRO (multitrack) and I have been told that Audio Evolution is also able to record from a USB source.