Perceptual Roughness of Spatially Assigned Sparse Noise
for Rendering Reverberation

Abstract

Multichannel auralizations based on spatial room impulse responses often employ sample-wise assignment of an omnidirectional response to form loudspeaker responses. This leads to sparse impulse responses in each reproduction loudspeaker and the auralization of transient signals can sound rough. Based on this observation, we conducted a listening test to examine the general phenomenon of roughness due to spatial assignment. First, participants assessed the roughness of both Gaussian noise and velvet noise, assigned sample-wise to up to 36 loudspeakers by two algorithms. The first algorithm assigns channels merely by selecting random indices, while the second one constrains the time between two peaks on each channel. The results show that roughness already occurs when few channels are used and that the assignment algorithm influences it. In a second experiment, virtualizations of the test were used to examine the factors contributing to increased roughness. We systematically show the effect of spatial assignment on noise and conclude that besides time-differences, level-differences caused by head-shadowing are the principal cause for the perceived roughness. The results have significance in spatial room impulse response rendering and spatial reverberator design in general.

Motivation: Roughness in Broadband Parametric SRIR Methods

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Omnidirectional RIR
Distributed to 45 loudspeaker channels using SDM [1]
Rendered Non-Transient Signal
Rendered Transient Signal
Idealized Case: Distributed Gaussian Noise

Stimuli Experiment II.a

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Reference: Independent Gaussian
Independent Velvet Noise
Constrained Gaussian
Unconstrained Gaussian
Dense Constrained Velvet (T=0.0461 ms)
Dense Unconstrained Velvet (T=0.0461 ms)
Constrained Velvet (T=0.5 ms)
Unconstrained Velvet (T=0.5 ms)

Stimuli Experiment II.b

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Perfect Sum
Omnidirection Receiver, Time Aligned
Omnidirection Receiver
Diotic, Level Aligned
Diotic, Time Aligned
Diotic
Binaural
Binaural (T=0.5 ms)

References

[1] S. Tervo, J. P├Ątynen, A. Kuusinen, T. Lokki, "Spatial Decomposition Method for Room Impulse Responses," J. Audio Eng. Soc., vol. 61, no. 1, pp. 17-28 (2013 Mar.).