Oscillations, Waves, and Interactions - GWDG

Specific signal types in hearing research 53
Figure 10. Masked thresholds for Gaussian noise (dashed lines) and low-noise noise maskers
(solid lines) as a function of frequency offset between the masker and target. Squares show
100-Hz wide maskers and circles 10-Hz wide maskers both presented at 70 dB SPL.
center frequency. For low-noise noise (circles), however, we see a clear dependence of
thresholds on the center frequency. Although low-noise noise thresholds were lower
than Gaussian noise thresholds already at a center frequency of 1 kHz, for 10 kHz we
see a much larger difference of more than 15 dB which is much more similar to the
difference observed for sinusoidal and Gaussian noise maskers. The higher thresholds
for lower frequencies are well in line with the idea that peripheral filtering affects the
temporal envelope flatness of low-noise noise.
A variant of the experiment by Kohlrausch et al. [34] investigated the effect of a
frequency offset between masker and sinusoidal target signal with the target always
higher in frequency than the masker [35]. The addition of the sinusoidal target to
the masker band creates modulations with a rate that is characterized by the frequency
difference between target and masker. When the target is centered within
the masker, the newly introduced modulations will have a rate comparable to those
already present within the masker alone and will therefore be difficult to detect.
When the target is sufficiently remote from the masker band, the modulations that
will be introduced due to addition of target will be of considerably higher rate than
those already present within the masker and may be much easier to detect. There
is evidence that the auditory system exhibits some frequency selectivity associated
with the processing of temporal envelope fluctuations, which led to the modulation
filterbank model proposed by Dau et al. [36].
In Fig. 10 results of the experiment by van de Par and Kohlrausch [35] are shown.
Thresholds for Gaussian noise (dashed lines) and low-noise noise (solid lines) maskers
are shown centered at 10 kHz, for various target-to-masker frequency offsets and two
masker bandwidths. As can be seen for the squares showing the 100-Hz wide maskers,
the low-noise noise thresholds (squares with solid lines) are roughly independent of
frequency offset. The Gaussian noise thresholds for the same bandwidth (squares