Technology Behind the Hearing Aids Grand Rounds Round 1 Web Seminar Recorded July 17, 2014

Transcription

1 Technology Behind the Hearing Aids Grand Rounds Round 1 Presented by Laurel A. Christensen, PhD; Jason A. Galster, PhD; and Francis K. Kuk, PhD Technology Behind the Hearing Grand Rounds Laurel A. Christensen, PhD Chief Audiology Officer GN ReSound Group LChristensen@gnresound.com Overview The cases and information presented will emphasize that: wireless systems are not the same in terms of system architecture. Differences in how data is transmitted Differences in how the end user interfaces with the device wireless hearing systems provide greater end-user benefits than hearing aids alone. 1

2 Hearing Systems NOT Hearing Aids Hearing Systems NOT Hearing Aids Wireless technologies Near Field Magnetic Induction (NFMI) Bluetooth (RF) + Induction Radio Frequency (RF) 2

3 Wireless systems based on Near Field Magnetic Induction (NFMI) combined with Bluetooth (RF) GHz A/D Coding Radio (bluetooth) Decoding Coding Radio (bluetooth) NFMI radio transmitter radio receiver Bluetooth radio frequency is used for communication between an accessory and a Gateway device and NFMI transmission is used from the Gateway device to the hearing instruments. Wireless systems based on Near Field Magnetic Induction (NFMI) combined with Bluetooth (RF) NFMI transmission is used from the Gateway or Intermediary device to the hearing instruments NFMI part of the system contains the transmission energy within a localized magnetic field. This type of transmission is referred to as near-field transmission (up to 1 meter). The carrier frequency is generally 10-14MHz. Gateway device is typically worn around the neck as the hearing instruments/user needs to be within the NFMI field/little bubble to pick up the signal. Wireless systems based on Near Field Magnetic Induction (NFMI) combined with Bluetooth (RF) Advantages: Longer battery life due to low current drain on hearing instruments Drawbacks: Short transmission distance (max 1 meter) Need to wear Gateway device /streaming device around the neck Sound quality is affected by orientation of the gateway device and HA receiver coil and any delay introduced by relay between components 3

4 Wireless systems based on Proprietary radio frequency (RF) A/D Coding Radio (proxímity) 2.4 GHz 900 MHz/US 868 MHz/EU Radio In wireless systems based on proprietary radio frequency the radio frequency is used for direct communication between the accessory and hearing instruments. Wireless systems based on Proprietary radio frequency (RF) and Bluetooth LE The proprietary radio frequency system uses a radio to generate an electrical wave and an antenna to send the information. Uses ISM bands - Industrial, Scientific and Medical Frequency Band 900 MHz (US, Greenland, & some eastern Pacific Islands). 868 MHz (EU). 2.4 GHz Bluetooth LE made for iphone (mfi) use 2.4 GHz providing a direct connection to the iphone Wireless systems based on Proprietary radio frequency (RF) Advantages: No intermediary device (neck worn streamer) Drawbacks: Drawback: Battery Life Long distance signal transmission (7 meters) Low latency (18 ms) from source to listener no echo problems Connect to multiple audio devices; multiple users connect to the same audio source 4

5 How the End User Interacts With the System is Key to End User Benefits of the System Market research (Groth & Anthonsen, 2010) in defining user requirements to a hearing instrument system with wireless features. MarkeTrak (Kochkin) Less than 30% of wireless hearing aids are sold with accessories. WHY? Conclusions of (2010)Market Research NFMI Systems Research points out that the use of wireless accessories predominantly overcomes the negative effects of distance, background noise, poor room acoustics and hearing instrument feedback (when using the phone). Customer satisfaction increases when their ability to function in many listening situations improves. Available NFMI wireless accessories are perceived to have immature technologies, suffering from instable connections and system artifacts, and having complex set-up systems. Dispensers sell wireless accessories primarily when the end-user is familiar with using mobile phones and/or headsets or has hearing difficulties when watching TV. End User Requirements for WL System No need for body-worn device devices Connectivity to television and cell phone Long range of connection; stable connection Excellent audio quality None/minimal delay of streamed sound (no lip sync problems) for TV Connect to multiple audio devices; multiple users connect to the same audio source 5

6 CASES ACCESSORIES HAVE BENEFITS BEYOND THE HEARING AID Case 1: DL Age:65 (Male) Extensive History of Noise Exposure from Farm Equipment Experience: 5~7year (2 different premium hearing aids) Product Fitted: LiNX961 Wireless mfi device with connections to accessories Occupation: Consultant Concerns: Important that the device did not have a neck worn device he had rejected that in the past. Hearing aids alone were not working in many environments needed solutions for TV and in noisy situations as well as on the phone. Case 1: DL Audiometric Data Hint Score = 0.94dB 6

7 Case 1: DL Fitting Screen / Gain Settings Case 1: DL Benefit measures: Speech Reception in Noise Aided Omni: db Speech Reception in Noise Aided Directional: db Significant improvement understanding speech in background noise. Case 1: DL Hearing Aid Satisfaction Survey: 7

8 Case 1: DL - Accessories Fit TV Streamer Mini Mic Utilizes the mfi capability with his iphone Case 1 DL - Patient Reports The iphone connection makes phone calls very clear. Favorite part of iphone direct connection is remote control where VC and Programs can be very discreetly controlled. Uses the TV streamer everyday and finds this much better than the hearing aids alone. Mini Microphone allows him to hear in noisy environments where his hearing aids are useless. Direct Control Apps 24 8

9 Mini Mic Results Comparison to Directionality and FM SNR (db) Adaptive Directionality FM system/ha mic Mini mic/ha mic Case 2: BM Age:50 (Female) Experience: 18 years Product Fitted:LiNX961 HP Occupation: Social worker Needs: Sufficient amplification and good sound quality for her job working with elderly. Needs a good phone solution which has been a struggle and ability to stream to TV in order to be able to hear it properly. Case 2: BM Speech Reception in Noise Unaided: 16.6 db 9

10 Case 2: BM Case 2: BM Speech Reception in Noise Aided Omni: -1,3 db Speech Reception in Noise Aided Directional: -5,2 db Significant improvement understanding speech in background noise with hearing aids compared to without hearing aids. Significant improvement understanding speech in background noise when using a bilateral directional setting compared to an omni-directional setting. Case 2: BM Hearing Aid Satisfaction Survey: 10

11 Case 2: BM Accessories Fit iphone connectivity TV streamer Case 2 : BM Patient Reports Using TV streamer with good success Phone calls with direct streaming are working well Likes the sound quality Case 3: JD Age:83 (Male) Noted a hearing loss in his 70s gradually progressive Businessman serves on several boards Experience: 6 years (2 Different Premium WL Hearing Aids -NFMI) Has never been told about WL accessories Product Fitted: Verso 977 BTE Verso device with connections to accessories Occupation: Semi-retired Concerns: Not hearing well in noise, parties, TV, and in conference rooms 11

12 Case 3: JD Case 3: JD Accessories Fit Mini Mic TV streamer Case 3: JD Patient Reports Noted right away a feeling he could hear more of what was around him in noise he talked about sitting at a round table of 10 people and not being able to hear the people right beside him This is due to the sound processing the aids Binaural Directionality He uses the Mini Mic extensively in many settings and noted that his wife was very happy with this is party environments. Reported that he could hear much better when watching TV using TV streamer. 12

13 Case 4: TD Case 4: TD Recommendation: Fit with technology that could be combined with a mini mic that is worn by the assisting surgeon. Successfully fit with LiNX 961 and mini mic Summary Cases that give examples that WL hearing aids should be used with WL accessories for greater end user benefits. Dispensers need to rethink hearing aids and change to hearing systems that can help patients hear successfully in more environments. 13

14 On the Prescription of Remote Microphones Agenda Definition of Remote Microphone Wireless Audio Transmission Protocols Frequency Modulated (FM System) Bluetooth and Near-field Magnetic Induction (NFMI) 900 MHz 2.4 GHz Remote Microphone Research Conclusions 14

15 Room Acoustics Direct Signal Late Reverberation Early Reverberation Total Speech Signal Level CD Distance (Boothroyd, 2005) What is a remote microphone? Hearing assistive technology often paired with hearing aids FM systems are the most known example Today s wireless technologies are making remote microphones more accessible to more patients Remote microphones decrease the distance between a talker s mouth and the receiving microphone. 10 db improvement in SNR is the most commonly cited acoustic advantage 15

16 Wireless Audio Transmission Protocols Frequency modulation (FM) Bluetooth paired with near-field magnetic induction (NFMI) 900 MHz 2.4 GHz FM Systems Bluetooth Paired with Near-Field Magnetic Induction (NFMI) 16

17 900 MHz 2.4 GHz Comparative Research Study Remote Microphones using Four Wireless Audio Transmission Protocols 17

18 Experimental Goals This study documented behavioral outcomes of four different commercially available remote microphone systems Hearing in Noise Test (HINT) 20 sentences per condition Unaided and aided Hearing aid microphones on and off Two seated positions 6 and 12 feet Both within the room s critical distance Test Setup 6 Feet Streaming Data 18

19 12 Feet Streaming Data * * * * Streaming with Hearing Aid Microphone * * * * * * * * 6 feet 12 feet But patient reports conflict with documented benefits Why? 19

20 Recordings 1. 6 in front of mouth below mouth (lapel) below mouth, 24 out to table Conclusions Modern remote microphones offer improvements to speech understanding in noise that are consistent with FM benefits Overcome negative effects of distance No differences between 6 feet and 12 feet Even with the hearing aid microphone turned on, significant improvements in speech recognition in noise were achieved Counseling is required for greatest success References Boothroyd, A. (2004). Hearing aid accessories for adults: The remote FM microphone. Ear & Hearing, 25(1), Chisolm, T.H., Noe, C.M., McArdle, R., & Abrams, H. (2007). Evidence for the use of hearing assistive technology by adults: The role of the FM system. Trends in Amplification, 11(2), Lewis, M.S., Crandell, C.C., Valente, M., & Horn, J.E. (2004). Speech perception in noise: Directional microphones versus frequency modulation (FM) systems. Journal of the American Academy of Audiology, 15,

21 Thank You GRAND ROUNDS IN TECHNOLOGY BEHIND HEARING AIDS IMPORTANCE OF HIGH INPUT STAGE HEADROOM Francis Kuk, PhD, Widex ORCA-USA CASE: IS THE OLD BETTER THAN THE NEW? 60 yr male musician. Worn analog (Widex A9 BTE) for 10 years. Pleased with HA performance. Fitted with new premium digital hearing aids AU with adaptive directional mic Generally pleased with performance Complaints Not hearing well in noise Distortions heard when playing piano, singing, listening to concerts The old A9s are better than the new digital HAs Actions by audiologist Decrease gain for high input Increase MPO setting Turn on/off NR, dir mic Nothing helps. The distortions persist What can be done? X X X X X X 21

22 DISTORTIONS CAN OCCUR AT ANY STAGE OF HEARING AID PROCESSING Encoding Decoding Original sound Wireless system Hearing aid Sound Output Input stage Microphone ADC DSP processes compression adaptive Output stage Receiver DAC DYNAMIC RANGE OF SOUNDS AND MICROPHONE LIMITS - ANALOG 115 db Microphone db DIGITAL HEARING AID Microphones Digital Signal Processing Receiver A/D DSP D/A Input Signal Output Signal Analog Binary (Digital) Analog

23 ANALOG TO DIGITAL CONVERTER Analog Binary (Digital) A/D Factors that affect the integrity of the A/D converter in preserving the naturalness of the original signals Sampling Frequency Bit Depth & Dynamic Range Internal Noise Battery Consumption Input Range SAMPLING FREQUENCY Sampling frequency at least twice the highest frequency in sample Higher sampling frequency, More details of input preserved (better sound quality) Larger sample size A/D - SAMPLING FREQUENCY Original Signal High Sampling Frequency Low Sampling Frequency 23

24 BIT RATE - QUANTIZATION NOISE 2 bits 4 bits Number of bits (n) increases, RESOLUTION increases (not related to magnitude of input) Quantization noise decreases A/D BIT RATE Original Signal High bit rate Moderate bit rate Low bit rate BIT RATE DYNAMIC RANGE 1 bit 3 bits 5 bits Number of bits (n) increases, RESOLUTION increases (not related to magnitude of input) #intervals = 2 n Example, 10 bits = 2 10 or 1024 intervals Dynamic range increases 1 bit = 6 db (idealized) Sound quality improves Larger data file 24

25 REALISTIC DYNAMIC RANGES 115 db Dynamic Range of ADC = S/N (Current = 82 db) Dynamic Range of 16 Bit Digital Audio = 96 db Microphone db ADC Circuit Noise Floor Quantization Noise Floor ADC EFFECT ON INPUT RANGE Insufficient bits bits I Insufficient bits bits I INPUT LIMITS 110 LOUD MUSIC SPORTS ARENA db SPL CINEMA PARTY CONVERSATION IN CITY NOISE ETC db SPL INPUT RANGE OF COMPARABLE HIGH-END HEARING AIDS 92 db SPL CONSTRUCTION SITE / TRAFFIC NOISE db SPL 80 ALONE AT HOME db SPL CONVERSATION db SPL FALLING LEAVES db SPL 20 0 db SPL WHISPER db SPL 25

26 HOW TO INCREASE INPUT LIMIT GO BACK TO ANALOG ALTERNATIVE STRATEGIES ANALOG HEARING AID None of the advantages of digital signal processing Limited DR because of higher noise floor Limited by microphone to 115 db SPL DIGITAL BENEFITS More selective in the information that is processed (and transmitted) saving power More ways to manipulate/control signal ensuring better sound quality Digital transmission has lower power requirement and broader bandwidth than analog transmission e.g., FM may drain HA at 3 ma on top of HA s own current drain Higher immunity against interfering noise ensuring better sound quality Sound Quality/Immunity Against Interference Digital Analog Distance / interference HOW TO INCREASE INPUT LIMIT SHIFT INPUT RANGE ALTERNATIVE STRATEGIES Hears high input Loses low input Noisy 0 db SPL Hears soft input, Loses high input 26

27 EFFECT OF INPUT RANGE ALLOCATION Input Level (db) db SNR 94 db SNR 82 db SNR 82 db SNR Clear Dream HA #1 HA #2 Hearing Aid HOW TO INCREASE INPUT LIMIT USE COMPRESSION LIMITING AT INPUT ALTERNATIVE STRATEGIES INPUT AGC (AUTOMATIC GAIN CONTROL) Avoid clipping artifacts Compromise sound quality and naturalness due to compression temporal smearing IMPACT OF INPUT COMPRESSION LIMITING 27

28 HOW TO INCREASE INPUT LIMIT MAKE MICROPHONE(S) LESS SENSITIVE ALTERNATIVE STRATEGIES Use of directional microphone (reverse focus) Step microphone (6dB/oct slope) Tape over microphones (both, not back or front only) Reduced audibility of soft sounds Reduced sound quality (loss of lows) HOW TO INCREASE INPUT LIMIT & DR INCREASE BIT SIZE ALTERNATIVE STRATEGIES Less chance of clipping More dynamic range Less quantization noise Increase current drain Not always necessary DYNAMIC RANGE AND TRUE INPUT TECHNOLOGY 115 db Dynamic Range Of CURRENT = 82 db Dynamic Range of True Input Tech ADC = 94 db) Dynamic Range of 16 Bit Digital Audio = 96 db 15 db Microphone ADC Circuit Noise Floor Quantization Noise Floor 28

29 DETERMINER OF ADC DYNAMIC RANGE: AMPLIFIER AS VOLTAGE MULTIPLIER INPUT AMPLIFIER OUTPUT Current AD CONVERTER SNR (or actual DR) = 82 db Signal = 80 % NOISE = 20 % Signal level Noise level SNR = 12 db DETERMINER OF ADC DYNAMIC RANGE: TRANSFORMER AS VOLTAGE MULITPLIER INPUT TRANSFORMER AMPLIFIER OUTPUT 1:2 SNR = 18 db Signal = 89% Signal level Transformed signal level Noise level NEW AD CONVERTER SNR = 94 db SNR IMPROVED BY 12 db NOISE = 11% THE SOLUTION LOUD MUSIC SPORTS ARENA db SPL CINEMA PARTY CONVERSATION IN CITY NOISE ETC db SPL TRUE-INPUT TECHNOLOGY 106 db SPL INPUT RANGE OF COMPARABLE HIGH-END HEARING AIDS 92 db SPL CONSTRUCTION SITE / TRAFFIC NOISE db SPL 80 ALONE AT HOME db SPL CONVERSATION db SPL 20 WHISPER db SPL FALLING LEAVES db SPL 0 db SPL 29

30 COMPARING TRUE INPUT TECHNOLOGY AND COMPRESSION LIMITER AT HIGH INPUT COMPARING TRUE INPUT TECHNOLOGY AND COMPRESSION LIMITER AT HIGH INPUT True Input Technology COMPARING TRUE INPUT TECHNOLOGY AND COMPRESSION LIMITER AT HIGH INPUT Compression Limit 30

31 WHICH HAS A HIGHER HEADROOM (103 VS 113 DB SPL? WHICH HAS A HIGHER HEADROOM (103 VS 113 DB SPL? WHICH HAS A HIGHER HEADROOM (103 VS 113 DB SPL? 31

32 DOES HAVING A HIGHER HEADROOM IMPROVE SPEECH UNDERSTANDING AT HIGH NOISE LEVEL? Ten experienced hearing aid wearers as subjects none has musical training Used C4 (current) and D4 (new ADC) with flex earmolds C4 input limit 103 db SPL, DR 82 db D4 input limit 113 db SPL, DR 94 db Average equivalent vent diameter about 2 mm dbhl Frequency (Hz) STIMULUS PREPARATION Recorded NU-6 (full list) through KEMAR with Zwislokci coupler and ER11 microphone; output filtered with diffuse field inverse (DFI) filter Hearing aids (C4 and D4) were programmed to a flat 50 db HL set to (a) omni mic, no NR (b) adaptive directional mic with NR. The same default MPO was used. Occluding earmold Speech front, noise sides and back at 106 db-c. SNR = -3, 0, and +3 Subjective test (of music and discourse passages) at 0 and -30 db re: saturation in CLEAR, about db SPL peak in a pairwise manner in quiet The output of the HA was about 1-2 db higher than the input level Subjects tested under headphone at loud, but not uncomfortable Test conditions and word lists were counterbalanced Double-blind design TEST YOURSELF AT +3 SNR Clear Dream 32

33 TEST YOURSELF AT +3 SNR Base Clear Dream TEST YOURSELF AT +3 SNR Base Clear Dream TEST YOURSELF AT +3 SNR Base Mop Clear Dream 33

34 TEST YOURSELF AT +3 SNR Base Mop Clear Dream TEST YOURSELF AT +3 SNR Base Mop Walk Clear Dream TEST YOURSELF AT +3 SNR Base Mop Walk Clear Dream 34

35 NU6 Absolute Score (%) Dream - Dir., NR Clear - Dir., NR Dream - Omni, no NR Clear - Omni, no NR Signal-to-Noise Ratio (db) Dream Improvement re: Own Aid (%) PAIRED COMPARISON OF STIMULI (MUSIC AND SPEECH) 35

36 CHASIN (2014) TAKE HOME MESSAGE CHECK TO MAKE SURE YOUR HEARING AID HAS A HIGH INPUT LIMIT AND A LARGE DYNAMIC RANGE (ASK FOR HIGHEST AND LOWEST LEVELS, NOISE FLOOR, CURRENT DRAIN) FKUK@WIDEX.COM 36