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dB types
dB SPL = sound pressure level, hearing aid performance, for each 20 dB increase sound intensity increases X10, threshold for detectability = 20 micropascals = 0 dB @1KHz
dB HL - hearing level, 0 dBHL therefore represents the threshold of detectability of each frequency for a normally hearing population
dBA - weighted scale, sound field assessments,
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Stimulus
- •Clicks (not freq specific)
- –Narrow band (2-4kHz)
- – Broad or wide band (1-4kHz)
- •Pure tone (freq specific eg 1,2,3,4kHz)
- –Tone burst (overall length >20ms)
- –Tone pips (overall length <20ms)
–Tone burst has a defined start (rise time),duration (plateau) and end (fall time); the plateau is longer than therise/fall time.
–Tone pips usually has a plateau which is the same or shorter than the rise/fall time
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Otoacoustic emissions
- Stimulus - broadband click 1-4 KHz, upward & downward deflection, ,1MS, 82 Db +/- 7
- Probe stability >80%=good
- Ratio - signal to noise ration @ 1,1.5,2,3,4 Khz >/ 3,3,6,6,6
- Need 3/5 to pass
- Red = noise, blue=emission
- Quiet ΣN = number of accepted responses
- Frequency band reproducability % (should be greater than 50%)
- Pass= hearing thresholds>30db
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Vibrotactile thresholds
- 25dB @ 250Hz
- 55 dB @ 500Hz
- 70dB @ 100Hz
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Rules of masking
- Rule 1
- Difference between not masked AC ≥ 40dB
- Rule 2
- Not masked BC is more acute than AC threshold by ≥ 10dB
- Rule 3
- Where rule 1 not applied and the BC of one ear is more acute by ≥40dB than the unasked ac threshold of the other ear
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