50. Microphone Arrays

This chapter introduces various types of microphone array beamforming systems and discusses some of the fundamental theory of their operation, design, implementation, and limitations. It is shown that microphone arrays have the ability to offer directional gains that can significantly improve the quality of signal pickup in reverberant and noisy environments.

Hands-free audio communication is now a major feature in mobile communication systems as well as audio and video conferencing systems. One problem that becomes evident to users of these systems is the decrease in communication quality due to the pickup of room reverberation and background noise. In the past, this problem was dealt with by using microphones placed close to the desired talker or source. Although this simple solution has proven to be quite effective, it also has its drawbacks. First, it is not always possible or desirable to place the microphone very close to the talkerʼs mouth. Second, by placing the microphone close to the talkerʼs mouth, one has to deal with rapid level variation as the talker moves his or her mouth relative to the microphone. Third is the negative impact of speech plosives (airflow transients generated by plosive sounds) and forth, microphone structure-borne handling noise has a detrimental effect. Finally, for directional microphone elements, there is also a nearfield proximity effect (where the frequency response of the microphone is modulated by the relative position of the microphone to the mouth). With these issues in mind, it is of interest to investigate other potential solutions. One solution is to use beamforming microphone arrays, which can offer significant directional gain so as to result in similar audio performance to that of closely placed microphones.