Audio functions are addressed through their audio interfaces. Each audio function has a single AudioControl interface and can have several AudioStreaming and MIDIStreaming interfaces.

• The AudioControl (AC) interface is used to access the audio Controls of the function whereas.
• The AudioStreaming (AS) interfaces are used to transport audio streams into and out of the function.
• The MIDIStreaming (MS) interfaces are used to transport MIDI data streams into and out of the audio function.

The collection of the single AudioControl interface and the AudioStreaming and MIDIStreaming interfaces that belong to the same audio function is called the Audio Interface Collection (AIC). A device can have multiple Audio Interface Collections active at the same time. These Collections are used to control multiple independent audio functions located in the same composite device.

The following seven different types of standard Units and Terminals that are considered adequate to represent most audio functions available today and in the near future:

• Input Terminal
• Output Terminal
• Mixer Unit
• Selector Unit
• Feature Unit
• Processing Unit
• Extension Unit