ANSI S3.42 1992 ELECTROACOUSTIC EVLUATION OF HEARING
AIDS USING BROAD BAND SIGNALS
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Complex and Pure-tone Signals in the Evaluation of Hearing Aid Characteristics
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Stemachowicz, P., Lewis, D., Seewald, R., and Hawkins, D.
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JSHR 33, 380-385
Fig. 1: Gain for Oticon E38P with pure tone input (60 dB SPL)
and complex stimulus (60 dB SPL).
Fig.2: Gain for Oticon E38P with pure tone input (60 dB SPL)
and a complex stimulus (70 dB SPL).
Fig. 3: Audiogram showing aided benefit. Open circles are
unaided thresholds; filled symbols are the amplified speech spectrum based
on complex input signal (triangles) and based upon pure-tone input (circles).
Fig. 4: Comparison of output for puretone vs. complex input.
ANSI S3.42-1992 Testing Hearing Aids with a Broad-Band Noise Signal
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Designed to test non-linear Hearing Aids with Broadband signals
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Gives Family of 4 Response Curves
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Inputs range from 40 to 90 dB SPL
ANSI S3.42-1992 Testing Hearing Aids with a Broad-Band Noise
Signal
Following graph taken
from information in the Frye Electronics manual. Additional information
available from:
http://www.frye.com
Definitions
NSPL90
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The root mean square (RMS) output sound pressure level (SPL) produced by
a hearing aid with its gain set at maximum and with a 90 dB RMS speech-weighted
noise input.
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Standard measurement bandwidth is limited to 200 to 5000 Hz…
Full On Noise Gain
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With the gain control on the hearing aid in the full-on position, the noise
gain is a single figure expressed in dB and is derived by subtracting the
overall RMS input SPL to the hearing from the RMS output SPL produced by
the hearing aid
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E.g., with a 50 dB RMS noise input, noise gain = output SPL – 50 dB
Root Mean Square
RMS is the square root of the mean of the sum of the instantaneous value
of a signal
RMS Calculation
Whereas…. Pure tone at 10 dB at 5 freq
10+10+10+10+10=???
=10 + 10 log BW
=10+ 10 log 5
=10+10*.699
=16.99
Hearing Aid Settings
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Adjust controls to the settings stated by the manufacturer
Noise Stimuli
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Speech Weighted
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Crest Factor-12 dB (ratio of peak to RMS value)
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Random or PseudoRandom
ACTUAL TESTS
WHAT STANDARDS NEXT?
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Will ANSI S3.42, 1992 work with hearing aids with noise reduction circuits?