director algorithm development gn resound r&d eindhoven ...pros and cons of hearing aids why...
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Trends in Hearing Aid Technology
Jos Leenen, MSEE + BoADirector Algorithm DevelopmentGN ReSound R&D Eindhoven, NL
September 2010
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Outline
Short intro, who are the Users of HA?
Benefits vs Costs for the User
HA Signal Processing
Wireless Connectivity
Conclusions & Trends
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Trends in HA Market Size
Trends: 1. Ageing of human populations, worldwide
2. Youngsters misusing their ears … (NL 12-15y 10%(!!) some permanent loss)
3. More access to HA in developing countries
4. Less stigma, less negative press (slow process, boost by open fittings)3
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Fundamental Limitation of Hearing Aids
amp speaker
damagedmic.
Impaired Ear, now seen as ‘Impaired’ Sound System
correction processor
Correcting System
mic.
amp speaker
mic.
A “nerdish” analogy
Perfect restoration of damaged hearing is generally NOT possible!4
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An actual patient: Ms DL (78y)Complaint: unbearably loud …
G80
G50
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An actual patient: Ms AL (51y)Complaint: Sudden unilateral HL (permanent) and tinnitus R
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Some subjective conclusions (40 patients)
Every hard of hearing person is unique, has her/his own story
“Fitting hearing aids is 10% technical and 90% psychological work” (an excellent audiologist with 20y experience, I agree) a good fitter optimally combines technical and psychological experience
Great majority of first users are:– shocked by sound quality (in negative sense, less in case of open fit)– shocked by the very loud volume (often resulting from deprivation)– have to do a great effort to get used to the HA (open fit helps!)
Experienced users generally– have accepted the drawbacks of HA as unavoidable (hard to change opinions)– are often fully depending on their HA in daily life, reliability is key
Open fittings are a big relief!!– used wherever possible wrt HL (and even where not optimal!)– sound quality of the anti feedback system sure is perceived
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Pros and Cons of Hearing Aids
Why wear hearing aids?
1.Improve audibility of wanted sounds (speech, speech again, music, some environment)
2.Improve intelligibility (of the specific speaker you want to understand, need improved S/N)
3.Mask tinnitus (by adding the external sound level)
4.De-recruitement of the ear (to normalize loudness perception)
5.Comfort others (like family), etc
Why NOT wear hearing aids?
Feedback Phone Use
Suboptimal FittingHandling problems
Occlusion / own voice
Loss of Localization
DistortionSignal Latency
System Noise Wind NoiseBandwidth Loss
Money & TimeDiscomfort in Wearing
Stigma
Empty Battery
Bad Press from Others
Too Loud !Impulse Noise
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Many Processing Tasks in Modern Hearing Aids
2 (or more) ADCs + pre and post filtering
Adaptive Beamforming
Band Splitting
AGC-I, for loudness restoration needed as a result of reduced dyn range of the user
Noise Reduction
Sound Classification, e.g. for automatic program switching / adaptation
De-reverberation
Sound Re-localization, e.g. with help of e2e communication
Frequency Lowering (shift bands into more sensitive regions)
Output limiting / AGC-O
Feedback cancelation
Combining Bands
Class-D output stage
…
Connectivity (wired wireless): Fitting, e2e, TV, Phone, MP3, …
User Interface handling
Storage of (sets of) fitting parameter
Data Logging (use time, UI, environment, etc) => Learning Algorithms
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Challenges in Hearing Aid DSP Design
Power Use … a few mW (
1 to 5) (market pull for less)
Needed Dyn Range …
90 dB (market pull for more)
Overall Latency …
< 3 to 5 ms, especially for open fittings
Freq Range …
100 Hz to 7…8 kHz (market pull for 10…15 kHz)
Output Level …
110 up to 145 dBSPL
New form factors … impacting beamforming and feedback cancelation
A lot of ‘independent’ adaptive filters active in one system (resulting overall behavior?)
At least 2 product family releases per year (a highly competitive business)
Market demands in HA specs grow faster than dev. budgets (and battery power)
Strong pressure on time to market and MIPS & Memory: do more with less resources
Combine / integrate DSP modules in a smart way => combined HS + SW engineering
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Chip Development
Year
Dev Cost per Chip
Important reason for hearing aid companies to merge !
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Modern Digital HA Structure
ADC
ADC
Beam
Former
Filter
Ban k
Per Band Processing(AGC, NR, etc)
&Output Proc.
+ Amp
Feedback
Canceller
Wireless
Audio
Wireless
Control
Battery
Manager
System
Clock
Voltage
Reference
Power
Supply
Ant
enna
Data
Logging
Memory
Steering
Learning
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Warped delay with FFT side branch
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Perceptually Shaped Signal Latency
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Example: Tradeoff in Noise Reduction
low optimal high
10
9
8
7
6
5
4
3
2
1
0
Per
son
al C
ost
F
un
ctio
ns
Amount of Noise Reduction
SpeechDistortion
Output Noise
Total Perceptual Cost
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Noise Reduction Improvements
low high
10
9
8
7
6
5
4
3
2
1
0
Per
son
al C
ost
F
un
ctio
ns
Amount of Noise Reduction
SpeechDistortion
Output Noise
Total Perceptual Cost
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Acoustics
Fitting mechanics
Mechanics
Battery dynamics
Chip design
Magnetics
DSP, anti feedback
Hearing Aids: Extremely Multi-disciplinary
All involve ways of feedback
Acoust => Acoust (in + outside case)
Mech => Mech (case, wires)
Mech => Acoust (vibr => sound)
Acoust => Mech (sound => vibr)
Mech => El (vibr => IC)
El-Magn => El-Magn (wires, IC)
El-Magn => El-Magn (telecoil)
El => El via supply, ground orsubstrate, class-D, …
Algorithmic interactions
…
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Feedback Compensation Principle
Hearing Aid AlgoInput
Feedback
Compensation
-+
+
Parasitic
Feedback Paths
Two Tasks:
Measure/estimate Feedback
Mimic Feedback with limited DSP resources
Output
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0 1 2 3 4 5 6 7-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0Handset at 0 cm (dotted=removed)
Frequency in kHz
dB
Leaky
Examples of Feedback Paths
0 1 2 3 4 5 6 7-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0 Handset at 0 cm (dotted=removed)
Frequency in kHz
dB
Unvented
0 1 2 3 4 5 6 7 -100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0Handset at 0 cm (dotted=removed)
Frequency in kHz
dB
Vented
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Example of Feedback Path Estimation
0 1 2 3 4 5 6 7 -70
-60
-50
-40
-30
-20
-10
0
dB
Frequency in kHz
Measured FB Path=Solid, Model=Dashed Line
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Sense and Nonsense in Feedback Cancelation
low high
9
8
7
6
5
4
3
2
1
0
To
tal
Dis
tort
ion
[%
]
Acoustic Gain
No Anti Feedback System
Headroom Improvement
Usable Headroom
Un-usable Headroom
“Audiology Driven”Anti Feedback System
“Marketing Driven”Anti Feedback System
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New Topic: Machine Learning Applications
From Wikipedia:
Machine learning is a scientific discipline that is concerned with the design and development of algorithms that allow computers to evolve behaviors based on empirical data.
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Why Need for Machine Learning Applications?Let’s take a very simple digital HA algorithm example:
15 frequency bands
AGC, 4 parameters: Tatt, Trel, CR, Gain
Noise Reduction, 3 parameters: Tatt, Trel, Gmin
Feedback cancellation, say 15 FIR taps
Beamforming, say 20 FIR taps
Resulting number of parameters = 15 x (4 + 3) + 15 + 20 = 140 (commercial HA have > 400)
Let’s assume (only) 5 candidate values (very low, low, normal, high, very high) for each one.
Total number of candidate parameter vectors = 5140
10100
… there are
1080 electrons in the universe …
So at face value, finding the optimal parameter values (called fitting) even in a very simple HA … is far more difficult than finding one specific electron in the universe …
By some (many?) fitters this is not even perceived as a problem (yet) … Currently this problem is dealt with using common sense and human experience. But with growing complexity of algorithms the fitting problem will grow even more.
We hope Machine Learning can help solving this huge problem in a more fundamental way.23
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‘Pre-Fitting’ HA Algorithms (long way to go)
HA Algorithm
Patient ModelAudio
Corpus
Data Base (of all past
experiments)
Machine Learning
optimization engine
Parameter vector
Sample selection
Task of the optimization engine is to select the next audio sample and parameter vector (based on all previous experiments) in such a way that the next experiment will provide the most increase in (the modeled) patient satisfaction.
In a second stage fitting the real patients is still needed of course.
Patient Model
Data Base
Algorithm evaluation
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ReSound UniteTM 2.4 GHz Wireless System
Audio Streamer BT Phone Link Remote Control USB Fitting Dongle
ReSound Alera: first hearing aid with 2.4 GHz wireless link
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ReSound UniteTM System Overview
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ReSound AirlinkTM – Wireless \fitting
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Conclusions & Trends
Market demands in hearing aids (algorithms and connectivity) grow faster than budgets and battery power, therefore ingenuity is needed to keep moving ahead
Hearing algorithm DSP design and parameter fitting are equally important (and difficult!) tasks in maximizing end-user satisfaction
Personal believe: In the future, machine learning applications will play an important role in the HA (and CI) algorithm design process to enable personalized fitting
Wireless connectivity is very much wanted, and is technologically challenging. Standardizing will be needed badly.
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Thank you!
Questions / remarks?
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