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LeAudio

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gainsettingunits the increment in db steps applied to all
gainsetting values
gainsettingminimum the minimum permitted value of gainsetting
gainsettingmaximum the maximum permitted value of gainsetting
table fields of the gain setting properties characteristic read only
in a further complexity aics allows an audio stream to have its gain controlled
automatically traditionally know n as automatic gain control or agc or man ually which
may either be by a vol ume control client or a local user control with changed values exposed
in the audio input state characteristic when control is automatic the server does not
support any changes made by the client the server can exp ose whether or not the client is
allowed to change the mode from automatic to manual or vice versa through the gainmode
field of the audio input state characteristic using the values shown in table
chapter volume audio input and microphone control
gainmode value description
manual only a client may not change these settings automatic only
manual manual but a client may change the gainmode to
automatic
automatic automatic but a client may change the gainmode to
manual
table meaning of the gainmode field values in the aics audio input state characteristic
having sorted that out we can move on to the audio input state and the audio inp ut control
point which work much as wed expect the audio input state contains four fields described
in table
name size octets
gainsetting
mute
gainmode
changecounter
table fields for the audio input state characteristic
the gainsetting exposes the current value of gain in gainsettingunits writing a value
of to mute will not affect the current gainsetting value so unmuting it by writing to
mute will return the gain to the previous value in gainsetting if the server is in automatic
gain mode it will ignore anything written to the gainsetting field
mute says whether the audio stream is muted value or unmuted value aics gives
us an additional option where the value of indicates that a mute fu nction is disabled the
final audio stream can still be muted using the vcs mute but by exercising this option the
individual input stream cannot be muted separately
the gainmode and the changecounter behave exactly as they do for vcs and vocs
again its an independent instantiation for each aics instance
setting the aics parameters is achieved by writing to the audio input state control point
characteristic with one of the five opcodes listed in table
section audio input control service
opcode opcode name description
x set gain setting sets the gain in increments of gainsettingunits x
db
x unmute unmutes unless mute is disabled
x mute mutes unless mute is disabled
x set manual gain mode changes from manual to automatic gain if
allowed
x set automatic gain
mode changes from automatic to manual gain if
allowed
table opcodes for the audio input control point characteristic
these all do pretty much what it says in the name although as weve already discovered there
are quite a number of caveats where the server can ignore them especially if it is not prepared
to give up control of the gain and mute functionality
the set gain setting opcode x takes the form shown in table
parameter size octets value
opcode x
changecounter to
gainsetting to
table format for the audio input control point characteristic set gain setting procedure
all of the other procedures use the same shorter format for their parameters shown in table
parameter size octets value
opcode x unmute
x mute
x set manual gain mode
x set automatic gain mode
changecounter to
table format for opcodes x x for audio input control point characteristic
as with vocs there are a few additional characteristics which can help with a user interface
the audio input type is used to identify the audio input stream with a read only te xt
description which can be used for a ui typical values in english are microphone hdmi
bluetooth etc these are set by the manufacturer
chapter volume audio input and microphone control
the audio input status exposes the current status of each aics audio stream if the value
is set to the audio stream is inactive if it is set to the audio stream is active
the audio input description allows for a more detailed description of an audio input which
is useful where there are multiple inputs of the same type such as multiple bluetooth or h dmi
inputs it may be set by the manufacturer or optionally made writable to allow a user to update
it
putting the volume controls together
the opening diagram showed how these three services work together figure shows a
typical implementation for a pair of stereo headphones which support both a blu etooth
connection and a local microphone
the volume for each ear is set by combining the single value in vcs with the audio
location specific value from the vocs instantiation for each ear either of the incoming
audio streams can be individually muted or have their gain controlled if the server allows it
whilst vcs provides a global mute function
figure typical implementation for a pair of headphones
figure shows a similar approach for the left hearing aid of a stereo pair because
only one channel is being rendered there is only one instance of vocs serving the left hearing
aid the other hearing aid in the right ear would be identical but with a vocs instance for
the right audio location
section microphone control