1. SIGNAL PROCESSING IN HEARING AIDS
October 2003

2. “An Australian research and technology company that develops new solutions for the expanding digital hearing aid and communications industry.”

3. A Venture Capital Backed Spin-Off from CRC HEAR
Bionic Ear Institute

4. A new amplification scheme so that cochlear implants and hearing aids can be used more effectively together
Electric hearing with
Cochlear implant
Acoustic hearing with
Hearing aid

5. 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.

6. Commercial hearing aids
Digital Signal Processors for ADROTM
Cochlear Implant
Hearing Aid
Research
Mipsy (desk-top)
Audallion (wearable)
DSP hearing aids
Products
SPrint™
Cochlear Ltd
Commercial hearing aids

7. Investment: ($5 million in 2 years) Main shareholders: Rothschilds Biosciences, Nanyang Ventures

8. Excellent research partners Sound processing expertise
Dynamic Team
Audiologists
Scientists
Research reputation
Excellent research partners
Sound processing expertise
Business Team
Engineers

9. Advances in Hearing Aid Technology

10. Products and services ADRO™
ADRO is hearing aid software based on a revolutionary technology that significantly enhances hearing aid performance for hearing impaired people.
ADROFit
Fitting software for ADRO
Premium hearing aid package
ADRO plus:
Feedback suppression
Directional microphone
Noise reduction
Customisation
Products customised to OEM’s needs

11. Strategic Alliance
Established with the only independent manufacture of low power digital signal processing chips to hearing aid and communications industry

12. ADRO achieves the improvements wearers really want
Recently collected market surveys of hearing aid users show:
95% seek better hearing of speech against background noise
88% seek better sound quality
83% would like to hear more soft sounds
: from Marke Trak VI - Kochkin, 2002)

13. ADRO is an alternative approach that automatically adjusts the sounds to suit all types of hearing loss

14. A real life situation

15. Multi-band compression hearing aid Same hearing aid using ADROTM
ADRO improves intelligibility in any background noise
Multi-band compression hearing aid
Same hearing aid using ADROTM

16. ADRO Significantly Improved Performance for Sentences in Babble

17. In the same clinical trial, ADRO improved performance for sentences in quiet
4.5% **
11.9%***
14.2%***
** p< *** p<0.001

18. Multi-band compression hearing aid Hearing aid using ADROTM
ADRO improves intelligibility at a distance.
Multi-band compression hearing aid
Hearing aid using ADROTM

19. TECHNICAL ASPECTS

20. 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

21. 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

22. Hearing impairment reduces the dynamic range
Uncomfortable
Too loud
Loud
Comfortable
Soft
Very soft
Inaudible
Loudness growth for normal
hearing
Example of a hearing loss

23. 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

24. 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

25. Dspfactory’s Toccata Plus processor
Small size
Power consumption ~ 600 μA at 1.4 V
Low clock rate MHz
Up to 2.56 MIPS
Incorporates a hardware FFT unit and an Input/Output Processor
Also includes EEPROM, ADCs, DACs and drivers

26. Dspfactory’s Toccata Plus processor
Input
Stage
IOP (Input Output Processor)
RCORE (DSP Core Processor)
WOLA (Weighted Overlap-Add) Coprocessor
EEPROM
PreAmps, ADCs and sampling circuitry
Stores programs, fittings and calibrations
Output
Stage
Executes assembler code to process time domain samples from the IOP or frequency domain samples from the WOLA
DACs and direct drive circuitry
Buffers samples from the input stage and going to the output stage
Calculates FFT, applies gains and outputs data to the IOP

27. Feedback Suppression
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

28. Feedback Suppression Without Feedback Suppression Activated
Amplitude
Time
With Feedback Suppression Activated
Amplitude
Time

29. Directional Microphones
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.

30. Directional Microphones
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

31. ADRO™

32. ADRO: Architecture (Toccata Plus)
FFT
ADRO
FFT
ADC
DAC
Microphone
Output Device (Receiver)
64 Channels
64 Channels
Output Stage
WOLA
RCore
Input Stage
IOP

33. Perceptual Dynamic Range

34. Perceptual levels and output targets
Threshold
Uncomfortable
Listener’s
dynamic
range
Maximum Output Level
Hearing aid output range
Comfort Target
Audibility Target
The perceptual dynamic range is define as the range between the threshold of hearing and the uncomfortable loudness level.
For the ADRO strategy, we use only a section of the whole of the dynamic range.
This is because the Audibility target is usually set above the threshold level unless the dynamic range is particularly narrow as found with severe and profound hearing losses, then the Audibility target will be placed on or sometimes slightly below the threshold level. At the top end, the Maximum Output Level is set conservatively at a loud level for each individual channel which leads to a greater overall loudness when all channels are working together. The loudness of the combination of channels depends on many factors, such as the level of the input signal, the maximum gain and the severity of the hearing loss.
Perceptual levels and output targets

35. Percentiles: 75 dB speech

36. 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 30th 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)

37. ADRO™ Architecture 90th percentile > comfort? Decrease the Gain
Comfort Rule
Comfort Rule
30th percentile < audibility?
Increase the Gain
Audibility Rule
Gain > maximum gain?
Maximum Gain Rule
Limit the Gain
Magnitude > maximum?
Maximum Output Rule
Limit the Output

38. ADRO™ Processing
Example of gain adjustments for a real world situation
ADRO™ with no additional noise reduction.
The graph shows the ADRO™ gains varying in real time.

39. 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

40. Technical Comparison ADRO™ Compression
Speech outputs for ADRO™ and compression hearing aids:
ADRO™
Compression
Female speaker with 4-talker babble at -10 dB signal-to-noise ratio.

41. ADRO™ Architecture (Toccata Plus)
Apply Gain
Limit to
Max Output Level
Apply Volume Control Gain
64 Channels out
64 Channels in
Adjust Gain
values
Calculate
Percentiles
Calculate
Magnitudes
Slowly adapting values
RCore
WOLA

42. What do users think of ADRO™?
In a blind clinical trial, the standard Hearing Aid Measure of Contrast questionnaire (Dillon 1994) showed ADRO was preferred to compression.

43. Implementing ADRO – Low risk path to new and innovative technology for hearing aid manufacturers
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
Dynamic Hearing provides customisation and technology support
Simple and effective solution for the OEM customers

44. Awards
ADRO awarded the CRC Association commercialization award (shared with Cochlear Ltd),
Federal Government START Grant awarded to accelerate product development in headset and communication device research

45. Track record
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

46. The Future ADRO - Clinically Proven - Customisable - Embedded software
COMMUNICATION DEVICES
Toccata Plus
Open platform DSPs
Headsets
AUDIOLOGIST
- Product education
- Training
- Support
- Australian Clinic
HEARING IMPAIRED PEOPLE
- Better hearing
- Cost effective solutions