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SIGNAL PROCESSING IN HEARING AIDS

SIGNAL PROCESSING IN HEARING AIDS. October 2003. “An Australian research and technology company that develops new solutions for the expanding digital hearing aid and communications industry .”. A Venture Capital Backed Spin-Off from CRC HEAR. Bionic Ear Institute.

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SIGNAL PROCESSING IN HEARING AIDS

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  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 Acoustic hearing with Hearing aid Electric hearing with Cochlear implant

  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. Digital Signal Processors for ADROTM

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

  8. 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 is hearing aid software based on a revolutionary technology that significantly enhances hearing aid performance for hearing impaired people. ADRO™ 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. ADRO improves intelligibility in any background noise Multi-band compression hearing aid Same hearing aid using ADROTM

  16. ADRO Significantly Improved Performance forSentences in Babble

  17. In the same clinical trial, ADRO improved performance for sentences in quiet 4.5% ** 11.9%*** 14.2%*** ** p<0.01 *** p<0.001

  18. ADRO improves intelligibility at a distance. Multi-band compressionhearing 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 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 - 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

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

  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. Without Directional Microphone With Directional Microphone 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)

  31. ADRO™

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

  33. Perceptual Dynamic Range

  34. Uncomfortable Threshold Perceptual levels and output targets Listener’s dynamic range Maximum Output Level Hearing aid output range Comfort Target Audibility Target

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

  38. ADRO™ Processing Example of gain adjustments for a real world situation ADRO™ with noadditional noise reduction. The graph shows theADRO™ gains varyingin 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. Speech outputs for ADRO™ and compression hearing aids: Technical Comparison ADRO™ Compression Female speaker with 4-talker babble at -10 dB signal-to-noise ratio.

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

  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

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