A Practical Beamformer-Postfilter System for Microphone Arrays on Seat Belts

Belt microphones are an elegant and interesting alternative to conventional microphones used for speech recognition or handsfree systems. Three microphones are integrated into safety belts of the car, which are placed around the shoulder and chest of the passenger after fastening the belt. When compared to common microphone positions such as mirror, center console etc., belt microphones offer an improved speech quality in terms of SNR (signal-to-noise ratio) as they are very close to the passenger's mouth. A microphone with the highest SNR on the belt is often selected. The performance can be further improved by combining all microphone signals to generate an enhanced output. In this contribution the signal combination is performed with a carefully controlled adaptive beamformer followed by a spatial postfilter. The system's overall performance designed for belt microphones is evaluated and compared with the single best belt microphone in terms of SNR and SIR (signal-to-interference ratio).