Matching Projection Decoding Method for Ambisonics System

The basic Ambisonics decoding method will break down when the playback loudspeakers distribute unevenly. This paper proposes a modified Ambisonics method, the matching projection decoding method, for solving this problem. The matching projection decoding method is a kind of the greedy algorithm. It firstly calculates the projection value of the object Ambisonics signal over each Ambisonics signal of loudspeakers, then the maximum projection value is assigned to the corresponding loudspeaker. This process is repeated until all the loudspeakers have been assigned a gain value. The objective and subjective experiments were performed to evaluate the proposed system and the basic system. Objective evaluation results show that the accuracy of the sound field generated by the matching projection decoding method is better than that of the basic method; and the subjective evaluation results show a more correct directional perception of the matching projection decoding method than the basic one.

1. Introduction

The 3D surround sound systems have entered movie theaters and the living rooms in the last decades. The key technology of such system is named the three-dimensional sound field reproduction, which can be divided into three group methods to implement such technologies: The first one is the Vector Based Amplitude Panning (VBAP) [1] which is an efficient sound field control technique that adjusts the amplitude of the signal assigned to the loudspeaker to control the perceived position of the human ear. The second method is the Wave Field Synthesis (WFS)[2]. Based on Huygens' principle, WFS method reconstruct the entire space by a large sound field loudspeaker array, which has a very wide audible range, particularly suitable for sound people share the retransmission request. The third method is Ambisonics, which is developed by Michael Gerzon in the early 1970s [3]. Ambisonics is promised because it can encode a given sound field with arbitrary accuracy and the encoding results directly describe the spatial properties of the sound fields without reference to the reproduction system.