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LeAudio

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figure architecture of a simple bluetooth hearing aid
when you take a hearing aid or earbud to pieces t he first surprise most people encounter is
the number of microphones in them to perform active noise cancellation you need one
microphone monitoring the ambient sound and a second one in the ear canal if you want to
pick up the users voice to send ov er the bluetooth link to their phone there will normally be
a bone conduction microphone helping to pick up and isolate the spoken voice from the
ambient thats the minimum however i ts common to include additional microphone s to
generate a beam form ing array to improve directionality other audio algorithms may be
included to detect the type of environment and further enhance the users voice the latter is
important as the microphones in earbuds and hearing aids arent located as close to the mou th
as designers would want them to be they may often be behind the ear
were about to see new regulations come into effect to measure the sound level in the ear
canal and warn users about potential hearing damage which will probably lead to even more
internal microphones the good news is that the re has been a lot of development in mems
microphones in the last few years partly driven by the demands of voice assistants these
innovations are enhancing directionality and beam steering so that they can follow you around
the room the advantage of mems over traditional microphone structures is that you can
integrate digital signal process ors into the microphone itself which reduces size and power
consumption its not unusual to find four or more microphones in the latest hearables these
inputs need to be mixed and dispatched to the different functions of the hearing aid
if the device contains both bluetooth technology and telecoil receivers the appropriate audio
needs t o be routed from them for earbuds which send control signals or audio streams to a
second one these all need to be routed via a sub ghz radio normally nfmi whilst the
primary signal is buffered to synchronise the rendering time at both earbuds
section whats in a hearable
at the output audio transducers have become smaller with traditional open coil structures
being challenged by micro miniature balanced armature transducers and audio valves the
market is also seeing the appearance of mems speakers offering high sound levels whilst
they are probably more suited to headphones at this stage the technology is likely to migrate
to earbuds
looking at the new use cases that are being made possible with bluetooth le audio this
processing can become very complex a noise cancelling earbud receiving a bluetooth stream
and allowing voice commands to be transmitted at the same time w ill need to separate the
voice component from the ambient sound and apply echo cancellation before transmitting
it whilst at the same time suppressing the ambient sound that is mixed with the incoming
bluetooth signal if the incoming bluetooth stream is being broadcast from the same source
as the ambient such as when youre in a theatre conference room or watching tv then this
all needs to be done whilst maintaining an overall latency of around msecs that is
challenging
managing a ll of this n eeds an application processor which controls the specialised audio
processing blocks to minimise power and latency in hearing aids these are normally
implemented in hardware rather than in a general purpose digital signal processor dsp
the applicat ion processor will also normally control the user interface where commands may
come from buttons or capacitive sensors on the hearing aid via the bluetooth interface or
from a remote control which may be using either a bluetooth technology or proprieta ry sub
ghz radio link most devices include an optical sensor to detect when it is removed from the
ear so that it can be placed into a sleep state finally there is a battery and power management
function many hearing aids still use zinc air batteri es which provide a better power density
than rechargeable batteries that provides two main advantages the battery life is longer
and they weigh less the weight is important if youre wearing a hearing aid all day which is
why most modern hearing a ids w eigh less than grams around half the weight of an airpod
thats just the electronics fitting all of this into an earbud or hearing aid is a further challenge
pushing the limits of flexible circuitry and multi layer packaging designers need to make it
comfortable ensure it doesnt fall out of your ear but also accomplish all of this whilst
maintaining a good auditory path so that neither the fi t nor the electronics packed into it
affects the quality of the sound you also need to consider the question of whether the hearing
aid occludes ie whether it blocks you r ear to stop ambient sound or is open to allow you to
hear both until recently it was felt that occlusion was necessary if you wanted to have
effective ambient noise cancellation but a few recent innovations suggest t hat may no longer
be the case com pletely blocking the ear canal can cause issues with a build up of humidity
especially for prolonged wearing so we will probably see more designs taking th e open
direction
none of this is easy which is one of the reasons that hearing aids remain expens ive however
a growing number of chip companies are offering reference designs which have already done
chapter the background and heritage
much of the work a long with partner programs with specialist consultancies offering design
expertise to reduce the time to market this is resulting in the consumer earbud market growing
at a phenomenal pace but were still just at the beginning of the possibilities for what you
can put in your ear
the most ambitio us hearable which has shipped so far was bragis dash as well as providing
true wir eless stereo they decided to add an internal mp player and flash storage allowing you
to leave your phone at home while youre out running or in the gym yet still be able to listen
to your stored music directly from the earbuds
figure the dash earbud from bragi the first real hearable
recognising that the ear is the best place on the body for most ph ysiological sensors bragi
equipped the dash with a plethora of sensors and features a total of nine degree s of freedom
movement sensing with an accelerometer magnetometer and gyroscope a thermometer a
heart rate monitor and a pulse oximeter they produced a very nice graphic showing all of
the elements with their relative sizes which is represented in figure it was a stunning
achievement but sadly it was more than t he market wanted at that time as fitness wristband
manufacturers discovered its surprisingly difficult to keep customers engaged with their
health data unlike music where they just devour someone elses content hea lth data needs
a lot of analytics to turn it into a compelling story for the user
section whats in a hearable
thats a catch that is illustrated in figure you need to capture a lot of data before you
have enough to turn in to anything valuable during that time you need to employ some very
expensive data scientists to try and develop some compelling feedback pay for the ongoing
cost of cloud storage and analytics as well as app updates for every new version of phone
operating system there is no guarantee that it will ever provide feedback which is compelling
enough for the user to pay a monthly subscription to support the ongoing development costs
without that insight users give up which is why so many fitness bands are now sitting at the
back of bedroom drawers it doesnt help that few companies making these devices have a
data analytics business background rather than a pure hardware business model
figure the catch of health and fitness data
the difficulty of developing an insight business model is why a lmost a ll of the million
earbuds which shipped in concentrat ed on just one thing playing content where the
user has a choice of multiple mature services to choose from i suspect that in time we will