Zusammenfassung
Loudness matches were obtained between unmodulated carriers and carriers
that were amplitude modulated either periodically (rates between
2 and 32 Hz, modulation sinusoidal either on a linear amplitude scale
or on a dB scale; the latter is called dB modulation) or with the
envelope of the speech of a single talker. The carrier was a 4-kHz
sinusoid, white noise, or speech-shaped noise. Both normally hearing
subjects and subjects with cochlear hearing loss were tested. Results
were expressed as the root-mean-square (rms) level of the modulated
carrier minus the level of the unmodulated carrier at the point of
equal loudness. If this difference is positive, this indicates that
the modulated carrier has a higher rms level at the point of equal
loudness. For normally hearing subjects, the results show: (1) For
a 4000-Hz sinusoidal carrier, the difference was slightly positive
(averaging about 0.7 dB). There was no significant effect of modulation
rate or level over the range 20-80 dB SL. (2) For a speech-shaped
noise or white noise carrier, the difference was close to zero, although
for large modulation depths it tended to be negative. There was no
clear effect of level (over the range 35-75 dB SPL) or modulation
rate. For the hearing-impaired subjects, the differences were small,
but tended to be slightly negative for both the 4000-Hz carrier and
the noise carriers, when the modulation rate was above 2 Hz. Again,
there was no clear effect of overall level. However, for dB modulation,
the differences became more negative with increasing modulation depth.
For modulation rates in the range 4-32 Hz, the results could be fitted
reasonably well using the assumption that the loudness of modulated
sounds is based on the rms value of the time-varying intensity of
the response of the basilar membrane (taking into account the compression
that occurs in the normal cochlea). The implications of the results
for the fitting of multi-band compression hearing aids and for the
design of loudness meters are discussed.
Nutzer