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see sensors return to hearables as the ear is the best place for a wearable device to measure
biometrics its stable it doesnt move much its close to blood flow and provides a good site
to measure core temperature its e verything that the wrist isnt but the industry has learnt
the lesson that data is also hard which means that the se sensors are likely to appear as minor
features al lowing companies with the analytic resources time to develop that compelling
feedback its what weve seen apple do with the watch its a long slow business
fortunately for earbud s there is already a compelling reason for consumers to buy them
which means that hearables can be a useful platform to experiment with other things
all of this translates to a vast amount of excitement in the market earbuds are the fastest
growing consumer product ever and the pace shows no sign of slowing for the res t of this
book well look at how bluetooth le audio can add to the excitement and increase that rate
of growth
chapter the bluetooth le audio architecture
chapter the bluetooth le audio architecture
bluetooth specification development follows a welldefined process it starts off with a new
work proposal which develops use cases and assesses the market need for any new feature
the new work proposal is usually generated by a small study group consisting of a few
companies who want the feature a nd is then shared and appraised by any others who are
interested in it at that point other bluetooth sig members are asked if theyre interested in
helping develop and prototype it in order to see if theres enough critical mass for it to happen
once that level of commitment has been demonstrated the bluetooth sig board of directors
reviews it and assigns it to a group to convert the initial proposal into a set of requirements
and to put more flesh on the use cases those requirements are reviewed to make sure they
fit into the current architecture of bluetooth technology without breaking it and then
development begins once the specification is deemed to be more or less complete
implementation teams from multiple member companies develop prototypes which are tested
against each other in interoperability test events which check that the features work and
meet the original requirements this also provides a good check that the specifications are
understandable and unambiguous any remaini ng problems get addressed at that stage and
once thats done and everything is shown to work the specifications are adopted and
published only at that stage are companies allowed to make products qualify them and start
selling them
although we alwa ys try to avoid specification creep during the process we almost always fail
so new features tend to get added to the original ones thats been particularly true in the
evolution of bluetooth le audio as its evolved from being a moderately simple sol ution for
hearing aids into its current form which provides the toolkit for the next twenty years of
bluetooth audio products to help understand why we have ended up with over twenty new
specifications it useful to look at that journey from the origin al use cases to see how the final
architecture was determined
the use cases
in the initial years of bluetooth le audio development we saw four main waves of use cases
and requirements drive its evolution it started off with a set of use cases which came from
the hearing aid industry these were focused on topology power consumption and latency
section the use cases
the hearing aid use cases
the topologies for hearing aids were a major step forward from what the bluetooth classic
audio profiles do so well start with t hem
basic telephony
figure shows the two telephony use cases for hearing aids allowing hearing aids to
connect to phones its an important requirement as holding a phone next to a hearing aid
in your ear often caus es interference
figure basic hearing aid topologies
the simplest topology on the left is an audio stream from a phone to a hearing aid which
allows a return stream aimed primarily at telephony it can be configured to use the
microphone on the hearing aid for capturing return speech or the user can speak into their
phone thats no di fferent from what hands free profile hfp does but from the
beginning the hearing aid requirements had the concept that the two directions of the audio
stream were independent and could be configured by the application in other words the
stream from the phone to the hearing aid and the return stream from hearing aid to phone
would be configured and controlled separately so that either could be turned on or off the
topology on the right of figure moves beyond anything that adp or hfp can do here
the phone sends a separate left and right audio stream to left and right hearing aids and then
adds the complexity of optional return streams from each of the hear ing aid microphones
that introduces a second step beyond anything that bluetooth classic audio profiles can
manage requiring separate synchronised streams to two independent audio devices
low latency audio from a tv
an interesting extension of the requirement arises from the fact that hearing aids may
continue to receive ambient sound as well as the bluetooth audio stream many hearing aids
do not occlude the ear occlude is the industry term for blocking the ear li ke an earplug
which means that the wearer always hears a mix of ambient and amplified sound as the
processing delay within a hearing aid is minimal less than a few milliseconds this doesnt
present a problem however it become a problem in a situa tion like that of figure
where some of the wearers family is listening to the sound through the tvs speakers whilst
the hearing aid user hears a mix of the ambien t sound from the tv as well the same audio
stream through their bluetooth connection
chapter the bluetooth le audio architecture
figure bluetooth le audio streaming with ambient sound
if the delay between the two audio signals is much more th an milliseconds it begins
to add echo making the sound more difficult to interpret which is the opposite of what a
hearing aid should be doing milliseconds is a much tighter latency than most
existing adp solutions can provide so thi s introduced a new requirement of very low
latency
although t he bandwidth requirements for hearing aids are relatively modest with a
bandwidth of khz sufficient for mono speech and khz for stereo music these could not
be easily met with the existing bluetooth codecs whilst achieving that latency requirement
that led to a separate investigation to scope the performance requirements for a suitable
codec leading to the incorporation of the lc codec which well cover in chapter
adding mor e users
figure adding in multiple listeners
hearing loss may run in families and is often linked with age so its common for there to be
more than one person in a household who wears hearing aids therefore the new topology
needed to support multiple hearing aid wearers figure illustrates that use case for two
people both of whom should experience the same latency
adding more listeners to support larger areas
the topology should also be scalable so that multiple people can listen as in a classroom or