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The human ear cannot distinguish between two sources of sound if they happen to reach within a specific time interval, typically 0.1 seconds apart. More than this, and they are perceived as separate sources.
Imagine the sound is reflected back to the ears. Assuming that the source is very close to the human, the difference between hearing the two sounds—the emitted sound and the reflected sound—may be more than the minimum time for perceiving distinct sounds. If this is the case, then the...

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Time-frequency-dependent directional analysis of room reflections using eigenbeam processing and von Mises-Fisher

Amy Bastine¹, Thushara D Abhayapala¹, Jihui Aimee Zhang¹

¹Audio & Acoustic Signal Processing Group, The Australian National University, Canberra, Australian Capital Territory 2600, Australia.

The Journal of the Acoustical Society of America

|June 1, 2022

Summary

This study presents a new model for analyzing room acoustics, focusing on how sound reflects off surfaces at different frequencies. The findings help improve spatial audio quality by understanding directional sound reflections.

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Area of Science:

Acoustics
Signal Processing
Spatial Audio

Background:

Optimizing spatial audio perception requires understanding frequency-dependent spatiotemporal features of reflected soundfields.
A reliable room acoustic analyzer is needed to assess spatial variations in decaying soundfields, considering surface properties and source directivity.

Purpose of the Study:

To introduce a time-frequency-dependent angular reflection power distribution model using a von Mises-Fisher (vMF) mixture function for reverberant soundfield analysis.
To develop a method for analyzing manifold properties of reverberant soundfields.

Main Methods:

Utilizing spatial correlation of higher-order eigenbeams to derive directional reflection power vectors.
Synthesizing these vectors into a vMF mixture model.
Introducing a "directivity time-span" measure to quantify anisotropic reflection duration.

Main Results:

Demonstrating directional power variations of early reflections and late reverberations across frequencies.
Proving the influence of source position, directivity, and room environment on reflection power distribution.
Showing that directivity time-span is independent of source positions.

Conclusions:

The proposed vMF mixture model effectively analyzes time-frequency-dependent angular reflection power distributions in reverberant soundfields.
The directivity time-span offers a novel metric for characterizing the decay of directional reflections.
The study validates the model's subband performance against established methods like eigenbeam multiple signal classification.