USB Device Class Definition for Terminal Types
Release 1.0 March 18, 1998 6
1 Introduction
The intention of this document is to describe in detail all the Terminal Types that are supported by the Audio Device Class. This document is considered an integral part of the Audio Device Class Specification, although subsequent revisions of this document are independent of the revision evolution of the main Audio Device Class Specification. This is to easily accommodate the addition of new Terminal Types without impeding the core Audio Device Class Specification.
1.1 Scope
The Audio Device Class Definition applies to all devices or functions embedded in composite devices. All audio signals inside an audio function start at an Input Terminal, pass through some Units, and leave the function through an Output Terminal. Units can manipulate the signal in various ways. Terminals represent the connections of the function to the outside world.
As part of the Terminal descriptor, the wTerminalType field specifies the vendor’s suggested use of the Terminal. For example, a pair of speakers is a more suitable target for music output than a telephone line. This feature allows a vendor to ensure that applications use the device in a consistent and meaningful way.
1.2 Related Documents
· Universal Serial Bus Specification, 1.0 final draft revision (also referred to as the USB Specification). In particular, see Chapter 9, “USB Device Framework”.
· Universal Serial Bus Device Class Definition for Audio Data Formats (referred to in this document as USB Audio Data Formats).
· Universal Serial Bus Device Class Definition for Terminal Types (referred to in this document as USB Audio Terminal Types).
· ANSI S1.11-1986 standard.
· MPEG-1 standard ISO/IEC 111172-3 1993.
· MPEG-2 standard ISO/IEC 13818-3 Feb. 20, 1997.
· Digital Audio Compression Standard (AC-3), ATSC A/52 Dec. 20, 1995. (available from
http://www.atsc.org)
· ANSI/IEEE-754 floating-point standard.
· ISO/IEC 958 International Standard: Digital Audio Interface and Annexes.
· ISO/IEC 1937 standard.
· ITU G.711 standard.
1.3 Terms and Abbreviations
None.
USB Device Class Definition for Terminal Types
Release 1.0 March 18, 1998 7
2 Terminal Types
The following is a list of possible Terminal Types. This list is non-exhaustive and will only be expandedin the future.
2.1 USB Terminal Types
These Terminal Types describe Terminals that handle signals carried over the USB, usually throughisochronous pipes. These Terminal Types are valid for both Input and Output Terminals.
Table 2-1: USB Terminal Types
| Terminal Type |
Code |
I/O |
Description |
| USB Undefined |
0x0100 |
I/O |
USB Terminal, undefined Type. |
| USB streaming |
0x0101 |
I/O |
A Terminal dealing with a signal carried over an endpoint in an AudioStreaming interface. The AudioStreaming interface descriptor points to the associated Terminal through the bTerminalLink field. |
| USB vendor specific |
0x01FF |
I/O |
A Terminal dealing with a signal carried over a vendor-specific interface. The vendor-specific interface descriptor must contain a field that references the Terminal. |
2.2 Input Terminal Types
These Terminal Types describe Terminals that are designed to record sounds. They either are physically part of the audio function or can be assumed to be connected to it in normal operation. These Terminal Types are valid only for Input Terminals
Table 2-2: Input Terminal Types
| Termina Type |
Code |
I/O |
Description |
| Input Undefined |
0x0200 |
I |
Input Terminal, undefined Type. |
| Microphone |
0x0201 |
I |
A generic microphone that does not fit under any of the other classifications. |
| Desktop microphone |
0x0202 |
I |
A microphone normally placed on the desktop or integrated into the monitor. |
| Personal microphone |
0x0203 |
I |
A head-mounted or clip-on microphone. |
| Omni-directional microphone |
0x0204 |
I |
A microphone designed to pick up voice from more than one speaker at relatively long ranges. |
| Microphone array |
0x0205 |
I |
An array of microphones designed for directional processing using host-based signal processing algorithms. |
USB Device Class Definition for Terminal Types
Release 1.0 March 18, 1998 8
| Terminal Type |
Code |
I/O |
Description |
| Processing microphone array |
0x0206 |
I |
An array of microphones with an embedded signal processor. |
2.3 Output Terminal Types
These Terminal Types describe Terminals that produce audible signals that are intended to be heard by the user of the audio function. They either are physically part of the audio function or can be assumed to be connected to it in normal operation. These Terminal Types are only valid for Output Terminals. The distinction between headphones, desktop speakers, and room speakers may be used by applications to select different 3D signal processing algorithms.
Table 2-3: Output Terminal Types
| Terminal Type |
Code |
I/O |
Description |
| Output Undefined |
0x0300 |
O |
Output Terminal, undefined Type. |
| Speaker |
0x0301 |
O |
A generic speaker or set of speakers that does not fit under any of the other classifications. |
| Headphones |
0x0302 |
O |
A head-mounted audio output device. |
| Head Mounted Display Audio |
0x0303 |
O |
The audio part of a VR head mounted display. The Associated Interfaces descriptor can be used to reference the HID interface used to report the position and orientation of the HMD. |
| Desktop speaker |
0x0304 |
O |
Relatively small speaker or set of speakers normally placed on the desktop or integrated into the monitor. These speakers are close to the user and have limited stereo separation. |
| Room speaker |
0x0305 |
O |
Larger speaker or set of speakers that are heard well anywhere in the room. |
| Communication speaker |
0x0306 |
O |
Speaker or set of speakers designed for voice communication. |
| Low frequency effects speaker |
0x0307 |
O |
Speaker designed for low frequencies (subwoofer). Not capable of reproducing speech or music. |
2.4 Bi-directional Terminal Types
These Terminal Types describe an Input and an Output Terminal for voice communication that are closely related. They should be used together for bi-directional voice communication. They may be used separately for input only or output only. These types require two Terminal descriptors. Both have the same type. The two Terminals are linked together through the bAssocTerminal fields in their respective Terminal descriptors. The Associated Interfaces descriptor can be used to reference a HID interface for conferencing functions.
USB Device Class Definition for Terminal Types
Release 1.0 March 18, 1998 9
Table 2-4: Bi-directional Terminal Types
| Terminal Type |
Code |
I/O |
Description |
| Bi-directional Undefined |
0x0400 |
I/O |
Bi-directional Terminal, undefined Type. |
| Handset |
0x0401 |
I/O |
Hand-held bi-directional audio device. |
| Headset |
0x0402 |
I/O |
Head-mounted bi-directional audio device. |
| Speakerphone, no echo reduction |
0x0403 |
I/O |
A hands-free audio device designed for host-based echo cancellation. |
| Echo-suppressing speakerphone |
0x0404 |
I/O |
A hands-free audio device with echo suppression capable of half-duplexoperation. |
| Echo-canceling speakerphone |
0x0405 |
I/O |
A hands-free audio device with echo cancellation capable of full-duplex operation. |
2.5 Telephony Terminal Types
These Terminal Types describe Terminals that connect to the PSTN or PBX. Initiating calls and monitoring call progress will be done through an associated interface which may be Communication, HID or Vendor-Specific class. These Terminals are bi-directional and follow the rules for bi-directional Terminals.
Table 2-5: Telephony Terminal Types
| Terminal Type |
Code |
I/O |
Description |
| Telephony Undefined |
0x0500 |
I/O |
Telephony Terminal, undefined Type. |
| Phone line |
0x0501 |
I/O |
May be an analog telephone line jack, an ISDN line, a proprietary PBX interface, or a wireless link. |
| Telephone |
0x0502 |
I/O |
Device can be used as a telephone. When not in use as a telephone, handset is used as a bi-directional audio device. |
| Down Line Phone |
0x0503 |
I/O |
A standard telephone set connected to the device. When not in use as a telephone, it can be used as a bidirectional audio device. |
2.6 External Terminal Types
These Terminal Types describe external resources and connections that do not fit under the categories of Input or Output Terminals because they do not necessarily translate acoustic signals to or from the user of the computer. Most of them may be either Input or Output Terminals.
USB Device Class Definition for Terminal Types
Release 1.0 March 18, 1998 10
Table 2-6: External Terminal Types
| Terminal Type |
Code |
I/O |
Description |
| External Undefined |
0x0600 |
I/O |
External Terminal, undefined Type. |
| Analog connector |
0x0601 |
I/O |
A generic analog connector. |
| Digital audio interface |
0x0602 |
I/O |
A generic digital audio interface. |
| Line connector |
0x0603 |
I/O |
An analog connector at standard line levels. Usually uses 3.5mm. |
| Legacy audio connector |
0x0604 |
I/O |
An input connector assumed to be connected to the lineout of the legacy audio system of the host computer. Used for backward compatibility. |
| S/PDIF interface |
0x0605 |
I/O |
An S/PDIF digital audio interface. The Associated Interface descriptor can be used to reference an interface used for controlling special functions of this interface. |
| 1394 DA stream |
0x0606 |
I/O |
An interface to audio streams on a 1394 bus. |
| 1394 DV stream soundtrack |
0x0607 |
I/O |
An interface to soundtrack of A/V stream on a 1394 bus. |
2.7 Embedded Function Terminal Types
These Terminal Types represent connections to internal audio sources or sinks in a device. All have associated interfaces for control. These interfaces may be HID or other classes (vendor-specific, mass storage for CD-ROM, etc.). Devices capable of both playback and recording should follow the rules for bidirectional Terminals.
Table 2-7: Embedded Terminal Types
| Terminal Type |
Code |
I/O |
Description |
| Embedded Undefined |
0x0700 |
I/O |
Embedded Terminal, undefined Type. |
| Level Calibration Noise Source |
0x0701 |
O |
Internal Noise source for level calibration (MPEG decoding, Dolby PrologicÔ, AC-3 etc.) |
| Equalization Noise |
0x0702 |
O |
Internal Noise source for measurements. |
| CD player |
0x0703 |
I |
Audio compact disc player or CD-ROM capable of audio playback. |
| DAT |
0x0704 |
I/O |
Digital Audio Tape. |
| DCC |
0x0705 |
I/O |
Digital Compact Cassette. |
最終更新：2011年06月04日 16:31
