Universal Serial Bus Device Class Definition for Audio Devices

Scope of This Release.........................................................................................................ii
Contributors........................................................................................................................ii
Revision History ..................................................................................................................ii
Table of Contents ................................................................................................................v
List of Tables ....................................................................................................................viii
List of Figures...................................................................................................................xiii
1 Introduction ................................................................................................................14
1.1 Scope....................................................................................................................14
1.2 Purpose .................................................................................................................14
1.3 Related Documents ...............................................................................................14
1.4 Terms and Abbreviations.......................................................................................14
2 Management Overview...............................................................................................17
3 Functional Characteristics.........................................................................................18
3.1 Audio Interface Class.............................................................................................18
3.2 Audio Interface Subclass and Protocol...................................................................18
3.3 Audio Synchronization Types.................................................................................19
3.3.1 Asynchronous .................................................................................................19
3.3.2 Synchronous...................................................................................................19
3.3.3 Adaptive .........................................................................................................19
3.4 Inter Channel Synchronization ...............................................................................19
3.5 Audio Function Topology .......................................................................................20
3.5.1 Input Terminal ................................................................................................21
3.5.2 Output Terminal..............................................................................................21
3.5.3 Mixer Unit .......................................................................................................22
3.5.4 Selector Unit...................................................................................................22
3.5.5 Feature Unit....................................................................................................23
3.5.6 Processing Unit...............................................................................................23
3.5.7 Extension Unit ................................................................................................28
3.5.8 Associated Interfaces......................................................................................28
3.6 Copy Protection .....................................................................................................28
3.7 Operational Model .................................................................................................29
3.7.1 AudioControl Interface ....................................................................................30
3.7.2 AudioStreaming Interface ...............................................................................31
4 Descriptors .................................................................................................................36
4.1 Device Descriptor ..................................................................................................36
4.2 Configuration Descriptor ........................................................................................36
4.3 AudioControl Interface Descriptors.........................................................................36
4.3.1 Standard AC Interface Descriptor....................................................................36
4.3.2 Class-Specific AC Interface Descriptor ...........................................................37
4.4 AudioControl Endpoint Descriptors ........................................................................57
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 vi
4.4.1 AC Control Endpoint Descriptors.....................................................................57
4.4.2 AC Interrupt Endpoint Descriptors...................................................................58
4.5 AudioStreaming Interface Descriptors....................................................................58
4.5.1 Standard AS Interface Descriptor....................................................................59
4.5.2 Class-Specific AS Interface Descriptor............................................................59
4.5.3 Class-Specific AS Format Type Descriptor .....................................................60
4.5.4 Class-Specific AS Format-Specific Descriptor.................................................60
4.6 AudioStreaming Endpoint Descriptors....................................................................60
4.6.1 AS Isochronous Audio Data Endpoint Descriptors ...........................................61
4.6.2 AS Isochronous Synch Endpoint Descriptor ....................................................63
5 Requests .....................................................................................................................65
5.1 Standard Requests ................................................................................................65
5.2 Class-Specific Requests ........................................................................................65
5.2.1 Request Layout...............................................................................................65
5.2.2 AudioControl Requests ...................................................................................68
5.2.3 AudioStreaming Requests...............................................................................94
5.2.4 Additional Requests ........................................................................................97
Appendix A. Audio Device Class Codes .......................................................................99
A.1 Audio Interface Class Code ...................................................................................99
A.2 Audio Interface Subclass Codes ............................................................................99
A.3 Audio Interface Protocol Codes..............................................................................99
A.4 Audio Class-Specific Descriptor Types...................................................................99
A.5 Audio Class-Specific AC Interface Descriptor Subtypes .......................................100
A.6 Audio Class-Specific AS Interface Descriptor Subtypes .......................................100
A.7 Processing Unit Process Types............................................................................100
A.8 Audio Class-Specific Endpoint Descriptor Subtypes.............................................101
A.9 Audio Class-Specific Request Codes ...................................................................101
A.10 Control Selector Codes........................................................................................102
A.10.1 Terminal Control Selectors ...........................................................................102
A.10.2 Feature Unit Control Selectors ......................................................................102
A.10.3 Processing Unit Control Selectors.................................................................102
A.10.4 Extension Unit Control Selectors...................................................................104
A.10.5 Endpoint Control Selectors ...........................................................................104
Appendix B. Example 1: USB Microphone (Informative)............................................105
B.1 Product Description .............................................................................................105
B.2 Descriptor Hierarchy ............................................................................................105
B.3 Descriptors ..........................................................................................................106
B.3.1 Device Descriptor .........................................................................................106
B.3.2 Configuration Descriptor ...............................................................................107
B.3.3 AudioControl Interface Descriptor .................................................................107
B.3.4 AudioStreaming Interface Descriptor.............................................................109
B.3.5 String Descriptors .........................................................................................112
B.4 Requests .............................................................................................................