The Audio Device Class Definition applies to all Devices or Functions embedded in composite Devices that are used to manipulate audio, voice, and sound-related functionality. This includes both audio data (analog and digital) and the functionality that is used to directly manipulate audio signals, such as Gain and Tone Control. The Audio Device Class does not include functionality to operate transport mechanisms that are related to the reproduction of audio data, such as tape transport mechanisms or CD-ROM drive control, nor does it include how HID features (volume up/down, play/pause, etc.) are conveyed. See Universal Serial Bus Device Class Definition for Human Interface Devices (HID) for more related information.
Specification
Device Class Specification