Digital technology

1
Digital hearing aids
Harvey Dillon National Acoustic
Laboratories (Australian Hearing) CRC for
Cochlear Implant and Hearing Aid Innovations
ASA Brisbane, 2001
2
Overview

• Digital signal processing (introduction)
• General concepts of compression
• Selecting signal processing features
• NAL-NL1 development and evaluation
• Real-ear gain testing of non-linear aids
• Fine-tuning of hearing aids
• Potential future signal-processing schemes

3
Digital signal processing (introduction)
Harvey Dillon National Acoustic
Laboratories (Australian Hearing) CRC for
Cochlear Implant and Hearing Aid Innovations
ASA Brisbane, 2001
4
Digital signal processing (introduction)
5
Analog and digitally-programmable block diagrams
Source Dillon (2001) Hearing Aids
Figure 3.2 Block diagram of an analog hearing
aid (top) and a digitally programmable hearing
aid (bottom).
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Digital signal processing
Microphone
Earphone
Processor
1 0 0 1 0 0 1 1 .
Analog to digital converter
Digital to analog converter
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(No Transcript)
8
3 4 6 7 5 5
3 2 1 0 2
3
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Recoding into bits (binary digits)
Code Binary value word
3 011 4 100 6 110 7 111
5 101 5 101 3 011 2 010
1 001 0 000 2 010 3 011
4s
1s
2s
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Digital signal processing
Microphone
Earphone
Processor
1 0 0 1 0 0 1 1 .
Analog to digital converter
Digital to analog converter
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Digital signal processing

• Sampling rate
• Number of bits
• Instructions per second
• Hard wired versus general arithmetic processor
  open platform
• Block processing (Fast Fourier Transform - FFT)
  versus sequential processing

12
Block diagram symbols
Source Dillon (2001) Hearing Aids