Ville Pulkki

Enhanced Direction Estimation Using Microphone Arrays for Directional Audio Coding

Modern home entertainment systems offer surround sound audio playback. This progress over known mono and stereo devices is also intended for high quality hands-free telephony to enhance intelligibility of speech in group conversation. Directional Audio Coding (DirAC) provides an efficient and well-established way to record and encode spatial sound and to render it at an arbitrary loudspeaker setup. On the recording site, DirAC is based on B-format microphone signals. These signals can be obtained by one omnidirectional and three figure-of-eight microphones pointing along the axes of a three-dimensional Cartesian coordinate system. However, a grid of omnidirectional microphones is more appropriate for consumer applications due to economic reasons. Arrays can provide the required figure-of-eight directionality only for a certain frequency range. However, in this contribution we show that a straightforward direction estimator is biased. After formulating the bias analytically we propose an unbiased estimator and derive the theoretical limits for unique direction estimation. The results are illustrated by means of simulations and measurements.

Directional Audio Coding Using Planar Microphone Arrays

Multichannel sound systems become more and more established in modern audio applications. Consequently, the recording and the reproduction of spatial audio gains increasing attention. Directional Audio Coding (DirAC) represents an efficient approach to analyze spatial sound and to reproduce it using arbitrary loudspeaker configurations. In DirAC, the direction-of-arrival and the diffuseness of sound within frequency subbands is used to encode the spatial properties of the observed sound field. The estimation of these parameters is based on an energetic sound field analysis using three- dimensional microphone arrays. In practice, however, physical design constraints make three-dimensional microphone configurations often not acceptable. In this paper, we consider a new approach to microphone array processing that allows for an estimation of both direction-of-arrival of sound and diffuseness based on planar microphone configurations. The performance of the proposed method is evaluated via simulations and real measured data.