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Should Hearing Aids Make Speech Normally Loud or Make Speech Clear

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Should Hearing Aids Make Speech Normally Loud or Make Speech Clear? ... VIOLA: targets. Input/output curves: Compression ratio and gains for 65 dB input (speech) ... – PowerPoint PPT presentation

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Title: Should Hearing Aids Make Speech Normally Loud or Make Speech Clear


1
Should Hearing Aids Make Speech Normally Loud or
Make Speech Clear?
  • Gitte Keidser and Frances Grant
  • National Acoustic Laboratories

2
Procedures for fitting non-linear hearing aids
  • LGOB, IHAFF, FIG6, DSLi/o, ScalAdapt Loudness
    Normalisation
  • NAL-NL1 Maximise Speech Intelligibility make
    overall loudness equal to, or less, than normal

3
International Long-term Average Speech Spectrum
4
Loudness perception
5
IHAFF NAL-NL1
  • Contour test loudness functions
  • VIOLA targets
  • Input/output curves Compression ratio and gains
    for 65 dB input (speech)
  • NAL-NL1 formula Threshold data as input -
    Frequency shaping and compression ratios as
    output

Wideband Compression threshold of 46 dB SPL Fast
time constants (2.5, 40) msec. MPO - half way
between the two prescriptions
Both rationales are implemented in two-channel
schemes
6
Subjects (24)
7
Prescribed gain, 65 dB input(NAL-NL1 - IHAFF)
Flat losses, N16
Sloping losses, N8
8
Prescribed CR
LF
HF
9
Laboratory Tests(KEPAR from Knowles)
  • Paired Comparison Test (preference with respect
    to clarity and ease of understanding speech)
  • Speech Recognition Test (BKB sentences)

10
Paired Comparison

Speech in quiet (avg. level)

11
Paired Comparison

NAL-NL1 IHAFF
12
Paired Comparison
13
Gain difference at 65 dB input after level
adjustment (NAL-NL1 - IHAFF)
IHAFF preferred
NAL-NL1 preferred
14
Speech recognition test

15
Summary, laboratory tests
  • In general, more subjects preferred NAL-NL1 than
    IHAFF - especially in noise listening to an
    average input level
  • Of the subjects who rated IHAFF higher than
    NAL-NL1, a majority had mild flat losses
  • On average, subjects performed significantly
    better with NAL-NL1 than with IHAFF when
    listening in traffic noise

16
Field test (JUMP-1 devices from
Oticon)
  • Test period four to six weeks
  • Three to seven individually selected everyday
    listening situations
  • Satisfaction (rating) and performance
    (descriptive) of each program

17
Field test
18
Field test
Difference
Distinct
Slight
Hardly any diff.
No difference
NAL-NL1 IHAFF
19
Field test observations
  • IHAFF sounds soft, muffled, dull, and echoey -
    comfortable and less noisy
  • NAL-NL1 makes speech clearer, and sounds more
    natural - loud in high level background noise
  • Low level noise intrusive on both programs

20
Conclusion
  • When there is a sufficient difference between
    targets, hearing impaired people prefer the
    rationale of Maximising Speech Intelligibility
    (NAL-NL1) to the rationale of Loudness
    Normalisation (IHAFF)

21
The end
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