Subject: Re: Directional microphone From: James Beauchamp <jwb(at)TIMBRE.MUSIC.UIUC.EDU> Date: Tue, 30 Apr 1996 08:03:16 -0600Argiris Kranidiotis writes: > Is it possible to simulate the effect of a highly directional >microphone using an array of two or more omni-directional microphones ? I >suspect that this could be done by using a simple time-delay filter,but I >am not sure how... Off the top of my head, here is my answer. Please correct me if anyone knows better. If you have two omini-directional (pressure) mikes spaced a distance small compared to a wavelength, and one of them is subjected to a time delay equal to the maximum delay that can exist between the two mikes (this depends on the angle of arrival of the sound wave), you can difference the two resulting signals and achieve a cardioid pattern, which is the basic unidirectional pattern. By elaborating on this scheme using several omni-directional mikes together with suitable delays and attenuation factors one can achieve a highly directional pattern. The closer the mikes are together, the wider the frequency range of operation. Therefore, for most applications the mikes might as well be built into a single enclosure. Design for a particular spatial pattern is very much like digital filter design for a particular frequency response. Jim Beauchamp j-beauch(at)uiuc.edu