Masking release by combined spatial and masker-fluctuation effects in the open sound field.

John C Middlebrooks

doi:10.1121/1.5014053

Abstract

In a complex auditory scene, signals of interest can be distinguished from masking sounds by differences in source location [spatial release from masking (SRM)] and by differences between masker-alone and masker-plus-signal envelopes. This study investigated interactions between those factors in release of masking of 700-Hz tones in an open sound field. Signal and masker sources were colocated in front of the listener, or the signal source was shifted 90° to the side. In Experiment 1, the masker contained a 25-Hz-wide on-signal band plus flanking bands having envelopes that were either mutually uncorrelated or were comodulated. Comodulation masking release (CMR) was largely independent of signal location at a higher masker sound level, but at a lower level CMR was reduced for the lateral signal location. In Experiment 2, a brief signal was positioned at the envelope maximum (peak) or minimum (dip) of a 50-Hz-wide on-signal masker. Masking was released in dip more than in peak conditions only for the 90° signal. Overall, open-field SRM was greater in magnitude than binaural masking release reported in comparable closed-field studies, and envelope-related release was somewhat weaker. Mutual enhancement of masking release by spatial and envelope-related effects tended to increase with increasing masker level.

Highlights

In a typical auditory scene, listeners can detect and recognize sounds of interest in the presence of other competing sounds. This task is aided by relative fluctuations in the envelopes of signals and maskers and by characteristics of interaural phase differences (IPDs), formalized in closed-field listening conditions as “binaural masking level differences” (BMLD)
The goal of the present work was to translate the study of combined binaural and envelope-related masking release from BMLD under headphones to spatial release from masking (SRM) in open sound field conditions
The present results demonstrate that both masker envelope fluctuation and spatial separation of signal and masker could enhance signal detection in a open field

Summary

Introduction

In a typical auditory scene, listeners can detect and recognize sounds of interest (signals) in the presence of other competing sounds (maskers). This task is aided by relative fluctuations in the envelopes of signals and maskers (often referred to as “monaural” masking release) and by characteristics of interaural phase differences (IPDs), formalized in closed-field (i.e., headphone) listening conditions as “binaural masking level differences” (BMLD). In real-world listening situations, monaural and binaural factors almost certainly interact. The present study explored possible interactions between such monaural and binaural factors using stimuli presented from loudspeakers positioned in front or 90 to the side of the listener. The two types of experiment differed with regard to the presence of energy in the masker spectra in flanking frequency bands and in the emphasis in the experimental design given to details of time-domain envelopes

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