Masking of Tonal Signals

Abstract

A review and experimental study of the phenomena of masking in relation to monaural, and binaural listening showed the following: (1) Subjects are more sensitive to a decrease in the level of a pure tone than in an increase. (2) The transient responses of a narrow filter are paralleled in subjects'' responses to short signals. (3) A large masking-level-difference (MLD) results from reversing the phase of a signal tone when it is added 90[degree] out of phase with a tone of the same frequency. (4) Substantial MLD''s are found with pure-tone maskers when the interaural phase of the signal is reversed, provided the signal is short. (5) Substantial MLD''s are found where a binaural signal is employed with uncorrelated noise at the two ears, providing the signal is short. (6) The increased MLD''s found for short signals are due to the fact that a different echanism is responsible for binaural detection than for monaural. (7) The absence of marked individual differences in the threshold for tones masked by noise is due to the large variation in the stimulus. (8) The threshold for the binaural detection of a change in the masker when a signal is added anti-phasically, is about 100 usec for a noise masker, and about 60 [mu]sec for a pure tone. In addition to the foregoing specific findings a few general conclusions are drawn: (1) There appears to be no evidence for "binaural inhibition"; when the MLD associated with a monaural signal and binaural noise is recognized as a binaural phenomenon, the other masking level differences all favor binaural listening. (2) There appears to be no evidence requiring the assumption of a sophisticated detector to explain monaural or binaural masking phenomena.