Universal Serial Bus Device Class Definition for Audio DevicesScope of This Release.........................................................................................................iiContributors........................................................................................................................iiRevision History ..................................................................................................................iiTable of Contents ................................................................................................................vList of Tables ....................................................................................................................viiiList of Figures...................................................................................................................xiii1 Introduction ................................................................................................................141.1 Scope....................................................................................................................141.2 Purpose .................................................................................................................141.3 Related Documents ...............................................................................................141.4 Terms and Abbreviations.......................................................................................142 Management Overview...............................................................................................173 Functional Characteristics.........................................................................................183.1 Audio Interface Class.............................................................................................183.2 Audio Interface Subclass and Protocol...................................................................183.3 Audio Synchronization Types.................................................................................193.3.1 Asynchronous .................................................................................................193.3.2 Synchronous...................................................................................................193.3.3 Adaptive .........................................................................................................193.4 Inter Channel Synchronization ...............................................................................193.5 Audio Function Topology .......................................................................................203.5.1 Input Terminal ................................................................................................213.5.2 Output Terminal..............................................................................................213.5.3 Mixer Unit .......................................................................................................223.5.4 Selector Unit...................................................................................................223.5.5 Feature Unit....................................................................................................233.5.6 Processing Unit...............................................................................................233.5.7 Extension Unit ................................................................................................283.5.8 Associated Interfaces......................................................................................283.6 Copy Protection .....................................................................................................283.7 Operational Model .................................................................................................293.7.1 AudioControl Interface ....................................................................................303.7.2 AudioStreaming Interface ...............................................................................314 Des criptors .................................................................................................................364.1 Device Des criptor ..................................................................................................364.2 Configuration Des criptor ........................................................................................364.3 AudioControl Interface Des criptors.........................................................................364.3.1 Standard AC Interface Des criptor....................................................................364.3.2 Class-Specific AC Interface Des criptor ...........................................................374.4 AudioControl Endpoint Des criptors ........................................................................57USB Device Class Definition for Audio DevicesRelease 1.0 March 18, 1998 vi4.4.1 AC Control Endpoint Des criptors.....................................................................574.4.2 AC Interrupt Endpoint Des criptors...................................................................584.5 AudioStreaming Interface Des criptors....................................................................584.5.1 Standard AS Interface Des criptor....................................................................594.5.2 Class-Specific AS Interface Des criptor............................................................594.5.3 Class-Specific AS Format Type Des criptor .....................................................604.5.4 Class-Specific AS Format-Specific Des criptor.................................................604.6 AudioStreaming Endpoint Des criptors....................................................................604.6.1 AS Isochronous Audio Data Endpoint Des criptors ...........................................614.6.2 AS Isochronous Synch Endpoint Des criptor ....................................................635 Requests .....................................................................................................................655.1 Standard Requests ................................................................................................655.2 Class-Specific Requests ........................................................................................655.2.1 Request Layout...............................................................................................655.2.2 AudioControl Requests ...................................................................................685.2.3 AudioStreaming Requests...............................................................................945.2.4 Additional Requests ........................................................................................97Appendix A. Audio Device Class Codes .......................................................................99A.1 Audio Interface Class Code ...................................................................................99A.2 Audio Interface Subclass Codes ............................................................................99A.3 Audio Interface Protocol Codes..............................................................................99A.4 Audio Class-Specific Des criptor Types...................................................................99A.5 Audio Class-Specific AC Interface Des criptor Subtypes .......................................100A.6 Audio Class-Specific AS Interface Des criptor Subtypes .......................................100A.7 Processing Unit Process Types............................................................................100A.8 Audio Class-Specific Endpoint Des criptor Subtypes.............................................101A.9 Audio Class-Specific Request Codes ...................................................................101A.10 Control Selector Codes........................................................................................102A.10.1 Terminal Control Selectors ...........................................................................102A.10.2 Feature Unit Control Selectors ......................................................................102A.10.3 Processing Unit Control Selectors.................................................................102A.10.4 Extension Unit Control Selectors...................................................................104A.10.5 Endpoint Control Selectors ...........................................................................104Appendix B. Example 1: USB Microphone (Informative)............................................105B.1 Product Des cription .............................................................................................105B.2 Des criptor Hierarchy ............................................................................................105B.3 Des criptors ..........................................................................................................106B.3.1 Device Des criptor .........................................................................................106B.3.2 Configuration Des criptor ...............................................................................107B.3.3 AudioControl Interface Des criptor .................................................................107B.3.4 AudioStreaming Interface Des criptor.............................................................109B.3.5 String Des criptors .........................................................................................112B.4 Requests .............................................................................................................