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figure typical implementation for a left hearing aid from a stereo pair
microphone control
although the examples above include microphones they are all using the microphone as a
local input which is selected or mixed with other audio inputs to be rendered however
microphones are also used as aud io inputs which are captured and sent back to an initiator
the microphone control service and profile mic s and mic p exist to provide device wide
control over microphones
the microphone control service is probably the simplest service in all of the bluetooth le
audio specifications comprising a single characteristic which provides a device wide mute
for microphones its simplest usage is shown in figure
figure simple usage of the microphone control service
there is no corresponding control point characteristic instead the mute characteristic can
be written directly as well as being read and notified it has the same features as the mute
field in the aics audio state characteristic namely
chapter volume audio input and microphone control
description value
not muted x
muted x
mute disabled x
figure mics mute characteristic values
if control of microphone gain is required mics should be combined with an instance of aics
figure although in this case mics doesnt provide much advantage over just using
aics however most clients would expect to use mics to perform a microphone mute
hence the reason to retain mics
figure combining the microphone service with an instance of the audio input control service
the combination of aics and mics makes more sense when multiple microphones exist as
mics gives the benefit of a device wide mute for the microphones which is its rea l purpose
figure
figure use of mics and aics for multiple microphones
finally mics can be used to provi de a device wide mute for multiple microphones as part of
a volume control scheme as shown in figure however in most cases multiple
microphones in an acceptor will be feeding directly into audio processing modules so its
unlikely that external control of individual microphones would be a requirement what figure
does is demonstrate the flexibility of volume and microphone control services in
bluetooth le audio
section a codicil on terminology
figure the combination of microphone and volume control services
a codicil on terminology
throughout this book ive been using the terms initiator acceptor and commander to
describe the three main types of device in the bluetooth le a udio ecosystem as i stated in
chapter these terms are defined as roles in cap so purists would probably object to my
conflating them with devices i still feel that conflation leads to a clearer understanding of
how everything fits together
potenti al for confusion exists in the way a commander as a device interacts with initiators
and acceptors as a role a commander can be collocated with an initiator but as a device
its interactions with an initiator and each of its acceptors can be confusing although all of
these interactions are covered by cap procedures they are independent figure
illustrates some of the profiles and service s described in this chapter in a simple case of an
initiator acceptor and independent commander
the spelling or misspelling of colocation and collocation can add further confusion these are
not alternative spellings but tota lly different words colocation with one l means in the same
place deriving from the latin locare in contrast collocation with two ls means working
together coming from the latin collegium
chapter volume audio input and microphone control
figure an example of profile and server relationships for volume and control
in this case three profiles are implemented in the commander two of them call control
and media control act on the complementary services in the initiator where as volume
control operates on the vcs vocs and aics instances in the acceptor for the
grammatically inclined the profiles in the commander and services in the initiator are
colocated the services in the acceptor are collocated
that brings us to the e nd of the gaf specifications the only other specifications within
bluetooth le audio are the top level profiles which we are about to come to
section a codicil on terminology
chapter top level bluetooth le audio profiles
chapter top level bluetooth le audio profiles
having covered everything in the generic audio framework we now come to the top level
profiles of bluetooth le audio although theyre still called profiles in most cases theyre a
lot simpler than the underlying profiles weve discussed or the bluetoo th classic audio
profiles instead of defining procedures they generally confine themselves to configuration
specifying new roles which mandate a combination of optional features and adding qos
requirements beyond those of bap in doing so they raise the bar by defining feature
combinations to meet commonly experienced use cases
in this chapter we will look at what these profiles contain as the y rely on features which are
already defined in the gaf specifications they do not have complementary serv ice
specifications hap the hearing access profile is the exception as the corresponding
hearing access service introduces a new presets characteristic for hearing aids tmap
the telephony media and audio profile has a nominal tmas service which is included in the
tmap specification the public broadcast profile has no service thats an anomaly that is
inherent with a broadcast application which does not expect a connection between initiator
and acceptor the lack of connection implies no poss ibility of a client server relationship
hence no opportunity for a service specification
a number of top level profiles are currently being developed in the bluetooth working groups
but the first three scheduled for adoption are
hap and has the hearing access profile and service which define