6 Higher-Order Directional Audio Coding

Archontis Politis and Ville Pulkki

Department of Signal Processing and Acoustics, Aalto University, Finland

6.1 Introduction

The first-order model of directional audio coding (FO-DirAC), detailed in Chapter 5, estimates a single direction of arrival (DoA) and a global diffuseness estimate that depend on the interactions of all the sound wave contributions arriving in a single observation window. If two source signals with similar spectra and incident from different directions are captured with nearly equal powers at the same time–frequency point, three scenarios can occur during FO-DirAC reproduction with perceivable effects. If the analysis of the B-format signals is computed through very short time averages, then the estimated DoA will fluctuate between the two true DoAs, with most estimates clustered around the true values. If no temporal smoothing is performed on the respective time–frequency gains applied during synthesis, then this directional distribution will be reproduced appropriately, with most power spatialized around the two DoAs, but with a high chance of perceived image instability and musical noise. If longer temporal smoothing is used on the spatialization gains, then most likely multiple loudspeakers will be activated between the two DoAs, resulting in a stable rendering but with an increased spatial blurring similar to linear or ambisonic decoding. On the other hand, if the DoA and diffuseness are computed using longer ...

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