Microphone Arrays: Fundamental Concepts

Abstract

Microphone array beamforming is concerned with the extraction of a desired acoustic signal from noisy microphone measurements. The microphone array problem is a more difficult one than that of classical sensor array applications due to several reasons: the speech signal is naturally analog and wideband. Moreover, the acoustic channel exhibits strong multipath components and long reverberation times. However, the conventional metrics utilized to evaluate signal enhancement performance do not necessarily reflect these differences. In this chapter, we attempt to reformulate the objectives of microphone array processing in a unique manner, one which explicitly accounts for the broadband signal and the reverberant channel. A distinction is made between wideband and narrowband metrics. The relationships between broadband performance measures and the corresponding component narrowband measures are analyzed. The broadband metrics presented here provide measures which, when optimized, hopefully lead to beamformer designs tailored to the specific nature of the microphone array environment.