Early Reflection Thresholds for Anechoic and Reverberant Stimuli within a 3-D Sound Display

Data on auditory thresholds for virtual acoustic reflections were obtained from 9 participants as a function of spatial position, time delay and stimulus type in a simulated 5.1 surround sound listening room environment. First-order reflections (3, 15 and 30 ms) were determined from a ray-tracing model of the listening room; their level was manipulated to simulate the overall effects of absorptive treatment. The direction of the reflection varied from 0 – 164 degrees offset from the direction of the simulated direct sound (corresponding to either the center or the right surround channel). Absolute thresholds (perception of any type of change) were measured at the 70.7% level using a one up-two down staircase algorithm, for anechoic and reverberant speech stimuli, and for tone burst stimuli (125, 250, 500, 1k, 2k and 4k Hz). For anechoic speech and tone stimuli, the threshold was 12 – 31 dB below the level of the direct sound; the addition of a reverberant decay (mid-band T30 = .6 s) raised thresholds by 7 dB. The results were in good agreement with previous threshold studies using real sound sources. The information is useful for determining engineering parameters for the real-time simulation of virtual acoustic environments, such as head-mounted displays that include head tracking.