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SIGNAL PROCESSING IN HEARING AIDS
October 2003
Signal Processing in Hearing Aids
“An Australian research and technology company that
develops new solutions for the expanding digital
hearing aid and communications industry.”
Signal Processing in Hearing Aids
Bionic Ear Institute
A Venture Capital Backed Spin-Off from CRC HEAR
Signal Processing in Hearing Aids
Electric hearing with
Cochlear implant
Acoustic hearing with
Hearing aid
A new amplification scheme so that cochlear implants and hearing aids can be used more effectively together
Signal Processing in Hearing Aids
The research goals were:
To make soft sounds more audible.
To ensure that loud sounds were comfortable.
To improve speech intelligibility in noise.
To maintain high sound quality.
Signal Processing in Hearing Aids
Cochlear Implant Hearing Aid
Research
1997-2002
Mipsy (desk-top) Mipsy (desk-top)
Audallion (wearable)
DSP hearing aids
ProductsSPrint™
Cochlear LtdCommercial hearing aids
Digital Signal Processors for ADROTM
Signal Processing in Hearing Aids
Investment: ($5 million in 2 years)Main shareholders: Rothschilds Biosciences, Nanyang Ventures
Signal Processing in Hearing Aids
Audiologists
Dynamic Team
Research reputation
Excellent research partners
Sound processing expertise
Scientists
Business Team Engineers
Signal Processing in Hearing Aids
Advances in Hearing Aid Technology
Signal Processing in Hearing Aids
ADRO™ ADRO is hearing aid software based on a revolutionary technology that significantly enhances hearing aid performance for hearing impaired people.
Fitting software for ADROADROFit
ADRO plus:
Feedback suppression
Directional microphone
Noise reduction
Products and services
Premium hearing aid package
Customisation Products customised to OEM’s needs
Signal Processing in Hearing Aids
Strategic Alliance
Established with the only independent manufacture of low power
digital signal processing chips to hearing aid and communications
industry
Signal Processing in Hearing Aids
95% seek better hearing of speech against background noise
88% seek better sound quality
83% would like to hear more soft sounds
ADRO achieves the improvements wearers really want
Recently collected market surveys of hearing aid users show:
: from Marke Trak VI - Kochkin, 2002)
Signal Processing in Hearing Aids
ADRO is an alternative approach that automatically adjusts the sounds to suit all types of hearing loss
Signal Processing in Hearing Aids
A real life situation
Signal Processing in Hearing Aids
ADRO improves intelligibility in any background noise
Multi-band compression hearing aid
Same hearing aid using ADROTM
Signal Processing in Hearing Aids
0
10
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100
MIL
D1
MOD1S
MOD2S
MOD3S
MOD4
MOD5
MOD6S
MOD7
MOD8S
MOD9
MOD10
MOD11
MOD12
S
MOD13
MOD14
SEV1
SEV3
SEV4
SEV5
Subject
Sc
ore
(%
)
ADROComp
ADRO Significantly Improved Performance forSentences in Babble
Signal Processing in Hearing Aids
4.5% ** 11.9%*** 14.2%***
In the same clinical trial, ADRO improved performance for sentences in quiet
** p<0.01 *** p<0.001
0
20
40
60
80
100
High Mid Low
Relative Speech Level
Se
nte
nc
e S
co
re (
%)
ADRO Compression
Signal Processing in Hearing Aids
ADRO improves intelligibility at a distance.
Multi-band compressionhearing aid
Hearing aid using ADROTM
TECHNICAL ASPECTS
Signal Processing in Hearing Aids
Introduction
What are the effects of a hearing loss?
DSP in hearing aids
– Dspfactory’s Toccata Plus processor
Dynamic Hearing’s strategies
– Feedback suppression
– Directional microphones
– The ADRO™ processing strategy
Signal Processing in Hearing Aids
What are the effects of a hearing loss?
Higher audibility threshold
Speech perception is reduced in noise
– A higher signal-to-noise ratio is required
– Reduced frequency resolution
– Reduced temporal resolution
Reduced dynamic range
– Elevated thresholds
– Near-normal sensitivity to loud sounds
Signal Processing in Hearing Aids
Hearing impairment reduces the dynamic range
20 30 40 50 60 70 80 90 100
dB HL
Example of a hearing loss
Loudness growth for normal hearing
Uncomfortable
Too loud
Loud
Comfortable
Soft
Very soft
Inaudible
Signal Processing in Hearing Aids
How can DSP help?
Higher audibility threshold– Provide extra gain in the required frequency bands by using
a digital filter
Require a higher signal-to-noise ratio– Directional microphone, noise cancellation algorithms and
matched filters can improve the SNR
Reduced dynamic range– Compression algorithms or the ADRO™ processing
strategy
Signal Processing in Hearing Aids
DSP in Hearing Aids
Digital hearing aids have been available since the mid 1990s
Early versions used ASICs (and some still do)
Most recently general purpose DSP processors optimised for
hearing aids have become available
The most widely used is the Dspfactory’s Toccata Plus
processor
Signal Processing in Hearing Aids
Dspfactory’s Toccata Plus processor
Small size
Power consumption ~ 600 μA at 1.4 V
Low clock rate - 1.28 MHz– Up to 2.56 MIPS
Incorporates a hardware FFT unit and an Input/Output Processor
Also includes EEPROM, ADCs, DACs and drivers
Signal Processing in Hearing Aids
Dspfactory’s Toccata Plus processor
PreAmps, ADCs and sampling
circuitry
IOP (Input Output Processor)
RCORE (DSP Core Processor)
Buffers samples from the input stage and going to the output stage
Output
Stage
DACs and direct drive
circuitry
WOLA (Weighted Overlap-Add) Coprocessor
Input
Stage
Executes assembler code to process time domain samples from the IOP or frequency domain samples from the WOLA
Calculates FFT, applies gains and outputs data to the IOP
EEPROM
Stores programs, fittings and calibrations
Signal Processing in Hearing Aids
Dynamic Hearing has developed a brand new solution to
an old problem
Feedback detection and suppression operates
independently in each of the 64 channels
Stops ringing while preserving the intelligibility of speech
Feedback Suppression
Signal Processing in Hearing Aids
Without Feedback Suppression Activated
Am
plitu
de
Time
With Feedback Suppression Activated
Am
plitu
de
Time
Feedback Suppression
Signal Processing in Hearing Aids
Dynamic Hearing has developed new techniques to increase
the signal-to-noise ratio.
Directional microphones provide a natural way to increase the
signal-to-noise ratio by reducing the amount of noise entering
the hearing aid from directions other than the front.
The majority of sound to be processed will come from in-front
of the hearing aid wearer.
Directional Microphones
Signal Processing in Hearing Aids
In this sample the hearing aid is worn by a listener (not free space)
Signal is directly in front of the wearer
Noise is 135° to the right of the wearer
Both the signal and the noise are presented at
the same level – 67dB (SPL A weighted)
Without Directional Microphone
With Directional Microphone
Directional Microphones
ADRO™
Signal Processing in Hearing Aids
ADRO: Architecture (Toccata Plus)
Microphone
ADC FFT ADRO FFT DAC
Output Device (Receiver)64 Channels
Input StageIOPRCoreWOLAOutput Stage
64 Channels
Signal Processing in Hearing Aids
Perceptual Dynamic Range
UCL
Threshold
Comfort
20
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120
250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000
frequency (Hz)
2 c
c co
up
ler
ou
tpu
t le
vel (
dB
)
Signal Processing in Hearing Aids
Perceptual levels and output targets
Comfort Target
Maximum Output Level
Audibility Target
Threshold
Uncomfortable
Listener’s
dynamic
range
Hearing aid output range
Signal Processing in Hearing Aids
Percentiles: 75 dB speech
20
30
40
50
60
70
80
250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000
frequency (Hz)
2 c
c co
up
ler
ou
tpu
t le
vel (
dB
)
Max
98th
90th
Leq
70th
50th
10th
Signal Processing in Hearing Aids
ADRO™ Architecture
An FFT is performed every 4 ms. A statistical analysis is then performed
on each of the 64 channels to calculate the 90th and 30th percentile
estimates.
The 90th percentile is compared to the comfort target value. The gain is
decreased if the target is exceeded. (Comfort Rule)
If the comfort rule did not decrease the gain, then the 30th percentile is
compared to the audibility target value. The gain is increased if the 30 th
percentile is lower than the target. (Audibility Rule)
If the gain is increased, it is limited to the maximum gain value.
(Maximum Gain Rule)
If the comfort rule and the audibility rule do not come into play, then the
gain is not changed.
The instantaneous output power in each bin is not allowed to exceed
the maximum output level (Maximum Output Rule)
Signal Processing in Hearing Aids
ADRO™ Architecture
90th percentile >
comfort?
30th percentile <
audibility?
Gain > maximum gain?
Magnitude > maximum?
Decrease the Gain
Increase the Gain
Limit the Gain
Limit the Output
Comfort Rule
Audibility Rule
Maximum Output Rule
Comfort Rule
Maximum Gain Rule
Signal Processing in Hearing Aids
ADRO™ with no
additional noise reduction.
The graph shows the
ADRO™ gains varying
in real time.
ADRO™ Processing
Example of gain adjustments for a real world situation
Signal Processing in Hearing Aids
ADRO™ (Adaptive Dynamic Range Optimisation)
Compression strategies
– Typically use only a few channels
– Fast attack and release times
– Vary gain based on signal input amplitude
ADRO™ strategy
– Uses 64 channels
– Long attack and release times
– Calculates long term estimates of the output signal’s dynamic range in each
channel
– Varies the gain in each channel so that the dynamic range of the output
signal is matched to the user’s requirements
Signal Processing in Hearing Aids
Technical Comparison
Speech outputs for ADRO™ and compression hearing aids:
ADRO™ CompressionFemale 75 dB Babble 85 dB
200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000
2 cc
Cou
pler
Out
put L
evel
(dB)
20
30
40
50
60
70
80
90
100
110
Female 75 dB Babble 85 dB
200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000
2 cc
Cou
pler
Out
put L
evel
(dB)
20
30
40
50
60
70
80
90
100
110
Female speaker with 4-talker babble at -10 dB signal-to-noise ratio.
Signal Processing in Hearing Aids
ADRO™ Architecture (Toccata Plus)
Apply Gain
64 Channels in
Limit to
Max Output Level
Apply Volume Control Gain
64 Channels out
Adjust Gain
values
Calculate
Percentiles
Calculate
Magnitudes
Slowly adapting values WOLARCore
Signal Processing in Hearing Aids
What do users think of ADRO™?
Hearing Aid Measure of Contrast ScaleADRO preferred 74% of the time in 25 listening situations
16%
10% 0% 12%
31%
31%
ADRO much better
ADRO better
ADRO slightly better
Comp slightly better
Comp better
Comp much better
In a blind clinical trial, the standard Hearing Aid Measure of Contrast
questionnaire (Dillon 1994) showed ADRO was preferred to compression.
Signal Processing in Hearing Aids
Immediate access to sophisticated technology - ADRO
runs in the dspfactory Toccata chipset
Product the result of several years research and
development with proven scientific benefit
Fast path to new product line
Implementing ADRO – Low risk path to new and innovative technology for hearing aid manufacturers
Dynamic Hearing provides
customisation and technology
support
Simple and effective solution for the OEM customers
Signal Processing in Hearing Aids
ADRO awarded the CRC
Association commercialization
award (shared with Cochlear Ltd),
Awards
Federal Government START Grant awarded to accelerate
product development in headset and communication device
research
Signal Processing in Hearing Aids
Dynamic Hearing has successfully licensed the
technology to French company Intrason, where the
hearing aid was enthusiastically received by the French
market – licensed January 2003, launched March 2003
Track record
Signal Processing in Hearing Aids
The Future
COMMUNICATION DEVICES
- Toccata Plus
- Open platform DSPs
- Headsets
HEARING IMPAIRED PEOPLE
- Better hearing
- Cost effective solutions
AUDIOLOGIST
- Product education
- Training
- Support
- Australian Clinic
ADRO
- Clinically Proven
- Customisable
- Embedded software