Temporal effects in simultaneous masking with on- and off-frequency noise maskers: Effects of signal frequency and masker level

Experiments 1 and 2 investigated the effect of frequency selectivity on comodulation masking release (CMR) in normal-hearing subjects, examining conditions where frequency selectivity was relatively good (low masker level at both low [500-Hz] and high [2500-Hz] signal frequency, and high masker level at low signal frequency) and where frequency selectivity was somewhat degraded (high masker level and high signal frequency). The first experiment investigated CMR in conditions where a narrow modulated noise band was centered on the signal frequency, and a wider comodulated noise band was located below the band centered on the signal frequency. Signal frequencies were 500 and 2000 Hz. The masker level and the frequency separation between the on-signal and comodulated flanking band were varied. In addition to conditions where the flanking band and on-signal band were presented at the same spectrum level, conditions were included where the spectrum level of the flanking band was 10-dB higher than that of the on-signal band, in order to accentuate effects of reduced frequency selectivity. Results indicated that CMR was reduced at the 2000-Hz region when masker level was high, when the frequency separation between on-signal and flanking band was small, and when a 10-dB level disparity existed between the on-signal and flanking band. In the second experiment, CMR was investigated for narrow comodulated noise bands, presented either without any additional sound or in the presence of a random noise background. CMR increased slightly as the masker level increased, except at 2500 Hz when the noise background was present. The decrease in CMR at 2500 Hz with the high masker level and with a noise background present could be explained in terms of reduced frequency selectivity. In a third experiment, we compared performance for equal absolute bandwidth maskers at a low (500-Hz) and a high (2000-Hz) stimulus frequency. Results here suggested that detection in modulated noise may be reduced due to a reduction in the number of quasi-independent auditory filters contributing temporal envelope information. The effects found in the present study using normal-hearing listeners under conditions of degraded frequency selectivity may be useful in understanding part of the reduction of CMR that occurs in cochlear-impaired listeners having reduced frequency selectivity.

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Ultrasonic frogs call at a higher pitch in noisier ambiance

Current Zoology ◽

10.1093/czoolo/61.6.996 ◽

2015 ◽

Vol 61 (6) ◽

pp. 996-1003 ◽

Cited By ~ 10

Author(s):

Fang Zhang ◽

Pan Chen ◽

Zhuqing Chen ◽

Juan Zhao

Keyword(s):

Fundamental Frequency ◽

Signal To Noise Ratio ◽

Low Frequency ◽

Environmental Noise ◽

Central China ◽

Signal Frequency ◽

Frequency Noise ◽

Acoustic Adaptation ◽

Adaptation Hypothesis ◽

Acoustic Adaptation Hypothesis

Abstract The ultrasonic communication in Concave-eared torrent frogs Odorrana tormota is believed to be an adaptation to avoid masking by the intense low-frequency noise of the rushing stream in their habitat. The acoustic adaptation hypothesis for ultrasonic origin predicts that some organisms subjecting to persistent acoustic interference from broadband, low-frequency environmental noise, might shift their signal frequency upward into frequency bands with lower noise energy. In other words, low-frequency environmental noise might cause upward shifts of species’ vocalization frequencies making their signals more conspicuous. Presently, it is unclear whether male O. tormota adjust their signal features in response to a change in the ambient noise level. We tested the prediction of the acoustic adaptation hypothesis by recording the vocalizations of male O. tormota inhabiting two streams with different background noise levels in Huangshan in central China and comparing their call features including the fundamental frequency (F0). Results showed that the spectrotemporal characteristics of the vocal signals of males in the two habitats were indifferent, except the duration of the call harmonic segments and three parameters related to the call fundamental frequency (F0). In terms of the F0, the pooled and individual frog data showed that frogs inhabiting the noisier habitat tended to emit calls having higher F0. The higher F0 increases the signal-to-noise ratio, thus benefiting the detection of vocalization. Thus, similar to several anuran species, concave-eared torrent frogs also display noise-dependent adjustment of vocal pitch in their vocalizations for making them more audible.

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Detection of a tone burst in continuous‐ and gated‐noise maskers; defects of signal frequency, duration, and masker level

The Journal of the Acoustical Society of America ◽

10.1121/1.381432 ◽

1977 ◽

Vol 61 (5) ◽

pp. 1298-1300 ◽

Cited By ~ 12

Author(s):

Craig C. Wier ◽

David M. Green ◽

Ervin R. Hafter ◽

S. Burkhardt

Keyword(s):

Tone Burst ◽

Signal Frequency ◽

Masker Level ◽

Gated Noise

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Masking release for gap detection

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.1992.0066 ◽

1992 ◽

Vol 336 (1278) ◽

pp. 331-337 ◽

Cited By ~ 5

Keyword(s):

Random Noise ◽

Detection Threshold ◽

Signal Frequency ◽

Frequency Noise ◽

Gap Detection ◽

Noise Masking ◽

Level Difference ◽

Masking Release ◽

Masking Level Difference ◽

Release From Masking

In random noise, masking is influenced almost entirely by noise components in a narrow band around the signal frequency. However, when the noise is not random, but has a modulation pattern which is coherent across frequency, noise components relatively remote from the signal frequency can actually produce a release from masking. This masking release has been called comodulation masking release (CMR). The present research investigated whether a similar release from masking occurs in the analysis of a suprathreshold signal. Specifically, the ability to detect the presence of a temporal gap was investigated in conditions which do and do not result in CMR for detection threshold. Similar conditions were investigated for the masking level difference (a binaural masking release phenomenon). The results indicated that suprathreshold masking release for gap detection occurred for both the masking-level difference (MLD) and for CMR. However, masking release for gap detection was generally smaller than that obtained for detection threshold. The largest gap detection masking release effects obtained corresponded to relatively low levels of stimulation, where gap detection was relatively poor.

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