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Failure to obtain comodulation masking release with frequency-modulated maskers
1Department of Experimental Psychology, University of Cambridge, England.
The Journal of the Acoustical Society of America
|June 1, 1988
Summary
Comodulation masking release (CMR) did not occur when maskers were frequency modulated, unlike with amplitude modulation. Correlated frequency modulation of maskers in different frequency bands does not reduce masking.
Area of Science:
- Auditory perception
- Psychoacoustics
- Signal processing in hearing
Background:
- Comodulation masking release (CMR) is a phenomenon where masking is reduced when multiple masker bands are modulated in amplitude by the same modulator.
- The current understanding of CMR primarily focuses on amplitude modulation (AM), with limited research on frequency modulation (FM).
Purpose of the Study:
- To investigate whether comodulation masking release (CMR) can be elicited by frequency-modulated (FM) maskers.
- To compare the effects of correlated versus uncorrelated FM maskers on auditory masking.
- To determine if CMR occurs when masker modulation is in frequency rather than amplitude.
Main Methods:
- Experiment I: Measured signal detection thresholds using two continuous sinusoidal maskers (one on-frequency, one flanking) that were either frequency modulated (FM) by a correlated or uncorrelated modulator.
- Experiment II: Utilized 25-Hz-wide noise maskers, with the on-frequency masker FM and the off-frequency masker either having the same FM or no FM.
- Investigated effects of masker presentation in different ears (interaural presentation).
Main Results:
- No significant difference in thresholds was found between correlated and uncorrelated FM maskers in Experiment I, indicating no CMR.
- No CMR was observed even when the flanking masker was presented to the ear opposite the signal.
- Similar thresholds were obtained in Experiment II regardless of whether the off-frequency masker shared the same FM as the on-frequency masker, confirming the absence of CMR.
Conclusions:
- Correlated frequency modulation (FM) of maskers in different frequency bands does not produce a masking release, unlike correlated amplitude modulation (AM).
- The mechanisms underlying CMR appear to be specific to amplitude modulation and do not extend to frequency modulation.
- These findings suggest that the auditory system's processing of comodulation differs significantly between amplitude and frequency domains.