USB audio uses synchronous transmission, interrupt transmission, and control transmission. All audio data is transmitted via synchronous transmission; interrupt transmission is used to forward information about the availability of the audio clock; control transmission is used to set the volume, request the sampling rate, etc. (see Figure).
Figure: Transfer between host and USB device - Synchronize IN and OUT for audio data, control for setting parameters, and interrupts for status monitoring.
The data requirements of the USB audio system depend on the number of channels, the number of bits representing each sample, and the sampling rate. The typical number of channels is 2 (stereo), 6 (5.1 channel) or higher (for studio or DJ applications). Although 16 bits are available for conventional audio, a typical sample rate is 24 bits, and high quality audio is 32 bits. Typical sampling rates are 44.1, 48, 96 and 192 kHz, the latter being used for high quality audio.