Fast processing models effects of reflections on binaural unmasking

Sound reflections and late reverberation alter energetic and binaural cues of a target source, thereby affecting its detection in noise. Two experiments investigated detection of harmonic complex tones, centered around 500 Hz, in noise, in a virtual room with different modifications of simulated room impulse responses (RIRs). Stimuli were auralized using the Simulated Open Field Environment’s (SOFE’s) loudspeakers in anechoic space. The target was presented from the front (0°) or 60° azimuth, while an anechoic noise masker was simultaneously presented at 0°. In the first experiment, early reflections were progressively added to the RIR and detection thresholds of the reverberant target were measured. For a frontal sound source, detection thresholds decreased while adding early reflections within the first 45 ms, whereas for a lateral sound source, thresholds remained constant. In the second experiment, early reflections were removed while late reflections were kept along with the direct sound. Results for a target at 0° show that even reflections as late as 150 ms reduce detection thresholds compared to only the direct sound. A binaural model with a sluggishness component following the computation of binaural unmasking in short windows predicts measured and literature results better than when large windows are used.