Influence of envelope distributions on signal detection

This paper examines if listeners are sensitive to changes in the envelope distributions by measuring thresholds of a 4-kHz sinusoidal signal in the presence of a 100-Hz wide bandpass-noise masker centred at the signal frequency. Three noise types were used: Gaussian noise, multiplied noise, and mixed noise, i.e. a weighted sum of the two noise types. For all masker types, thresholds were measured for a signal added in random phase to the masker. In addition, for the multiplied noise and mixed noise, thresholds were also measured for a signal added in phase to the carrier of the multiplied noise. Results show that thresholds for the signal added in random phase are similar for multiplied and mixed noise masker, whereas Gaussian noise produces thresholds higher than those for the two other masker types. Thresholds are generally higher when the signal was added in phase than the corresponding thresholds with the signal added in random phase. A model using the centroid of the mean envelope distribution qualitatively predicts the data. The results are discussed in the light of recent experiments on across-channel masking and comodulation masking release that employ off-frequency flanking bands, where it was hypothesised that off-frequency maskers interfere with the sensitivity to envelope cues at the signal frequency.