Oscillations, Waves, and Interactions - GWDG

Specific signal types in hearing research 57
• Role of masker fluctuations in off-frequency masking.
• Influence of the intrinsic envelope fluctuations of a noise on modulation detection.
• Effects of masker-signal phase relation in monaural and binaural on-frequency
masking.
The spectral selectivity of the auditory system is often studied by using narrowband
maskers [42]. A problem for the interpretation of masking data arises, when, due to
the use of tonal masker, distortion products or temporal cues like beats influence the
detection process [43]. In order to avoid the introduction of such “false cues”, one
often uses narrowband noise maskers instead [44]. It is implicitely assumed that this
substituion has no other effect than eliminating the mentioned artifacts.
In a study by van der Heijden and Kohlrausch [45] this assumption underlying the
power-spectrum model of masking [32,38] was tested for five different narrowband
maskers with the same center frequency. The masker types were either a sinusoid, a
Gaussian noise or a multiplied noise. The two noise signals had bandwidths of either
20 or 100 Hz. The five maskers thus differed in the amount of envelope variations: The
sinuoid has a flat envelope, the two noises have envelopes with intrinsic fluctuations,
with the multiplied noise having deeper envelope minima (see Sect. 3.2.2). The rate
of fluctuation of the envelopes was another experimental parameter, because it is
lower for the 20-Hz than for the 100-Hz masker.
In the experiments, these maskers had a center frequency of 1.3 kHz and were used
to mask a sinusoidal test signal at 2 kHz. The masker levels were varied between
60 and 84 dB. Figure 13 shows the growth-of-masking functions for the five masker
Figure 13. Simultaneous growth-of-masking
functions measured with various narrow-band
maskers centered at 1.3 kHz. The target was
a 2-kHz tone. The five curves indicate the
results for five different maskers: a sinusoid
(open circles), a 100-Hz-wide Gaussian noise
(filled squares), a 20-Hz-wide Gaussian noise
(open squares), a 100-Hz-wide multiplied noise
(filled triangles), and a 20-Hz-wide multiplied
noise (open triangles). Data points measured
with 20-Hz-wide maskers are connected with
dashed lines. Averaged data of six subjects
are plotted; error bars indicate ± one standard
deviation across the values of the six subjects.
Reused with permission from Ref. [45]. Copyright
1995, Acoustical Society of America.