James E. West
G. W. Elko
D. R. Morgan
R. A. Kubli
Acoust. Res. Dept., AT&T Bell Labs., 600 Mountain Ave., Murray Hill, NJ 07974
Directional microphones are best noted for their noise reduction properties in communication systems. Close-talking differential microphones are particularly useful when the noise environment disturbs the ability to communicate without error, such as in public and cellular telephony, aircraft communications, etc. These differential microphones work best when they are placed within 1 cm from the lips of the talker where the sound field has a large gradient. For a plane-wave sound field the sensitivity rises proportional to (omega)[sup n], where n is the order of the difference. Users of differential microphones do not always correctly position the sensor at the proper distance from the mouth and therefore the sensitivity of the microphone may also rise proportional to (omega)[sup n] especially at high frequencies. A method is described of correcting for this high-frequency gain without significantly degrading the noise canceling properties of first- and second-order differential microphones.