USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 76
Offset Field Size Value Description
0 bMute 1 Bool The setting for the addressed Mute
Control’s CUR attribute. Muted when
TRUE, not muted when FALSE.
In the second form, the Channel Number field is set to 0xFF. The parameter block contains a list of
settings for the CUR attribute for all available Mute Controls in the Feature Unit.
Table 5-17: Second Form of the Mute Control Parameter Block
Control Selector MUTE_CONTROL
wLength Number of available Controls: NrAv
Offset Field Size Value Description
0 bMute(1) 1 Bool The setting for the CUR attribute of the
first Mute Control.
… … … … …
NrAv-1 bMute(NrAv) 1 Bool The setting for the CUR attribute of the
last Mute Control.
5.2.2.4.3.2 Volume Control
The Volume Control is one of the building blocks of a Feature Unit. A Volume Control can support all
possible Control attributes (CUR, MIN, MAX, and RES). The settings for the CUR, MIN, and MAX
attributes can range from +127.9961 dB (0x7FFF) down to -127.9961 dB (0x8001) in steps of 1/256 dB or
0.00390625 dB (0x0001). The range for the CUR attribute is extended by code 0x8000, representing
silence, i.e., -¥ dB. The settings for the RES attribute can only take positive values and range from 1/256
dB (0x0001) to +127.9961 dB (0x7FFF). The Volume Control honors the request to the best of its
abilities. It may round the wVolume attribute value to its closest available setting. It will report this
rounded setting when queried during a Get Control request.
In the first form of the request, a particular Volume Control within a Feature Unit is addressed through
the Unit ID and Channel Number fields of the Set/Get Feature Unit Control request. The valid range for
the Channel Number field is from zero (the ‘master’ channel) up to the number of logical channels in the
audio channel cluster.
Table 5-18: First Form of the Volume Control Parameter Block
Control Selector VOLUME_CONTROL
wLength 2
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 77
Offset Field Size Value Description
0 wVolume 2 Number The setting for the attribute of the
addressed Volume Control:
0x7FFF: 127.9961 dB
…
0x0100: 1.0000 dB
…
0x0002: 0.0078 dB
0x0001: 0.0039 dB
0x0000: 0.0000 dB
0xFFFF: -0.0039 dB
0xFFFE: -0.0078 dB
…
0xFE00: -1.0000 dB
…
0x8002: -127.9922 dB
0x8001: -127.9961 dB
0x8000 -¥ dB (CUR
attribute only)
In the second form, the Channel Number field is set to 0xFF. The parameter block contains a list of
settings for an attribute of all available Volume Controls in the Feature Unit.
Table 5-19: Second Form of the Volume Control Parameter Block
Control Selector VOLUME_CONTROL
wLength (Number of available Controls: NrAv)*2
Offset Field Size Value Description
0 wVolume(1) 1 Number The setting for the attribute of the first
Volume Control.
… … … … …
(NrAv-1)*2 wVolume(NrAv) 1 Number The setting for the attribute for the last
Volume Control.
5.2.2.4.3.3 Bass Control
The Bass Control is one of the building blocks of a Feature Unit. The Bass Control influences the general
Bass behavior of the Feature Unit. A Bass Control can support all possible Control attributes (CUR, MIN,
MAX, and RES). The settings for the CUR, MIN, and MAX attributes can range from +31.75 dB (0x7F)
down to –32.00 dB (0x80) in steps of 0.25 dB (0x01). The settings for the RES attribute can only take
positive values and range from 0.25 dB (0x01) to +31.75 dB (0x7F). The Bass Control honors the request
to the best of its abilities. It may round the bBass attribute value to its closest available setting. It will
report this setting when queried during a Get Control request. Other parameters that also influence the
behavior of the Bass Control, such as cut-off frequency, cannot be altered through this request.
In the first form of the request, a particular Bass Control within a Feature Unit is addressed through the
Unit ID and Channel Number fields of the Set/Get Feature Unit Control request. The valid range for the
Channel Number field is from zero (the ‘master’ channel) up to the number of logical channels in the
audio channel cluster.
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 78
Table 5-20: First Form of the Bass Control Parameter Block
Control Selector BASS_CONTROL
wLength 1
Offset Field Size Value Description
0 bBass 1 Number The setting for the attribute of the
addressed Bass Control:
0x7F: +31.75 dB
0x7E: +31.50 dB
…
0x00: 0.00 dB
…
0x82: -31.50 dB
0x81: -31.75 dB
0x80: -32.00 dB
In the second form, the Channel Number field is set to 0xFF. The parameter block contains a list of
settings for all available Bass Controls in the Feature Unit.
Table 5-21: Second Form of the Bass Control Parameter Block
Control Selector BASS_CONTROL
wLength Number of available Controls: NrAv
Offset Field Size Value Description
0 bBass(1) 1 Number The setting for the attribute of the first
Bass Control.
… … … … …
NrAv-1 bBass(NrAv) 1 Number The setting for the attribute of the last
Bass Control.
5.2.2.4.3.4 Mid Control
The Mid Control is one of the building blocks of a Feature Unit. The Mid Control influences the general
Mid behavior of the Feature Unit. A Mid Control can support all possible Control attributes (CUR, MIN,
MAX, and RES). The settings for the CUR, MIN, and MAX attributes can range from +31.75 dB (0x7F)
down to –32.00 dB (0x80) in steps of 0.25 dB (0x01). The settings for the RES attribute can only take
positive values and range from 0.25 dB (0x01) to +31.75 dB (0x7F). The Mid Control honors the request
to the best of its abilities. It may round the bMid attribute value to its closest available setting. It will
report this setting when queried during a Get Audio Control request. Other parameters that also influence
the behavior of the Mid Control, such as cut-off frequency, cannot be altered through this request.
In the first form of the request, a particular Mid Control within a Feature Unit is addressed through the
Unit ID and Channel Number fields of the Set/Get Feature Unit Control request. The valid range for the
Channel Number field is from zero (the ‘master’ channel) up to the number of logical channels in the
audio channel cluster.
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 79
Table 5-22: First Form of the Mid Control Parameter Block
Control Selector MID_CONTROL
wLength 1
Offset Field Size Value Description
0 bMid 1 Number The setting for the attribute of the
addressed Mid Control:
0x7F: +31.75 dB
0x7E: +31.50 dB
…
0x00: 0.00 dB
…
0x82: -31.50 dB
0x81: -31.75 dB
0x80: -32.00 dB
In the second form, the Channel Number field is set to 0xFF. The parameter block contains a list of
settings for all available Mid Controls in the Feature Unit.
Table 5-23: Second Form of the Mid Control Parameter Block
Control Selector MID_CONTROL
wLength Number of available Controls: NrAv
Offset Field Size Value Description
0 bMid(1) 1 Number The setting for the attribute of the first
Mid Control.
… … … … …
NrAv-1 bMid(NrAv) 1 Number The setting for the attribute of the last Mid
Control.
5.2.2.4.3.5 Treble Control
The Treble Control is one of the building blocks of a Feature Unit. The Treble Control influences the
general Treble behavior of the Feature Unit. A Treble Control can support all possible Control attributes
(CUR, MIN, MAX, and RES). The settings for the CUR, MIN, and MAX attributes can range from
- 31.75 dB (0x7F) down to –32.00 dB (0x80) in steps of 0.25 dB (0x01). The settings for the RES attribute
can only take positive values and range from 0.25 dB (0x01) to +31.75 dB (0x7F). The Treble Control
honors the request to the best of its abilities. It may round the bTreble attribute value to its closest
available setting. It will report this setting when queried during a Get Control request. Other parameters
that also influence the behavior of the Treble Control, such as cut-off frequency, cannot be altered through
this request.
In the first form of the request, a particular Treble Control within a Feature Unit is addressed through the
Unit ID and Channel Number fields of the Set/Get Feature Unit Control request. The valid range for the
Channel Number field is from zero (the ‘master’ channel) up to the number of logical channels in the
audio channel cluster.
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 80
Table 5-24: First Form of the Treble Control Parameter Block
Control Selector TREBLE_CONTROL
wLength 1
Offset Field Size Value Description
0 bTreble 1 Number The setting for the attribute of the
addressed Treble Control:
0x7F: +31.75 dB
0x7E: +31.50 dB
…
0x00: 0.00 dB
…
0x82: -31.50 dB
0x81: -31.75 dB
0x80: -32.00 dB
In the second form, the Channel Number field is set to 0xFF. The parameter block contains a list of
settings for all available Treble Controls in the Feature Unit.
Table 5-25: Second Form of the Treble Control Parameter Block
Control Selector TREBLE_CONTROL
wLength Number of available Controls: NrAv
Offset Field Size Value Description
0 bTreble(1) 1 Number The setting for the attribute of the first
Treble Control.
… … … … …
NrAv-1 bTreble(NrAv) 1 Number The setting for the attribute of the last
Treble Control.
5.2.2.4.3.6 Graphic Equalizer Control
The Graphic Equalizer Control is one of the optional building blocks of a Feature Unit. The Audio Device
Class definition provides for standard support of a third octave graphic equalizer. The bands are defined
according to the ANSI S1.11-1986 standard. Bands are numbered from 14 (center frequency of 25 Hz) up
to 43 (center frequency of 20,000 Hz), making a total of 30 possible bands. The following table lists the
band numbers and their center frequencies
Table 5-26: Band Numbers and Center Frequencies (ANSI S1.11-1986 Standard)
Band Nr. Center Freq. Band Nr. Center Freq. Band Nr. Center Freq.
14 25Hz 24* 250Hz 34 2500Hz
15* 31.5Hz 25 315Hz 35 3150Hz
最終更新：2011年05月02日 03:34
