The role of modulation processing in binaural masking-patterns

Abstract

Binaural masking pattern experiments indicate a continuous decrease in the binaural masking-level difference (BMLD) with increasing spectral distance of a tonal signal to a narrowband noise masker. Previous studies suggested that this decrease in BMLD is due to additional modulation cues in monaural off-frequency masking conditions. An own masking pattern experiment with an additional interferer to mask modulation cues supported this hypothesis. The interferer is positioned spectrally below/above the masker for the signal above/below the masker with a spectral distance equal to the distance between masker and signal. This interference tone has a large impact on the thresholds without a binaural cue, as expected. Such an increase in the diotic thresholds is predicted on the basis of a modulation-filterbank model, but only if an across-channel modulation processing is assumed. The interferer also increases the dichotic thresholds, indicating an influence of modulations processing also in conditions where binaural cues are present. Assuming that modulation cues are masked by the interference tone and thus the detection is based on energy cues, the binaural data indicate effectively wider binaural filter, as previously suggested on the basis of notched-noise experiments.