Radio Telephone Noise Reduction by Voice Control at Receiver

TN transmitting speech over radio telephone circuits there are a number of conventional methods of increasing the signal with respect to the noise. Examples of such methods are the use of higher power, directive antennas, diversity reception and filters to narrow the received frequency band. In addition, there are other methods of a special character which reduce the effect of the noise interference with the speech transmission. One example of such a device limits the noise interference by eliminating the high peaks of noise of very short duration and depending upon the persistence of sensation of speech in the ear to bridge the gaps. Another method diminishes the noise in intervals of no speech. This is the method which will be discussed here. SPEECH AND N O I S E CONSIDERATIONS Speech signals may be represented by a group or band of frequencies occupying a certain interval of time. In using the conventional method of narrowing the received frequency band, filters eliminate all noise outside the band actually required. In fact we sometimes go beyond this and remove some of the outer frequency components of * Presented at the Pacific Coast Convention of A. I. E. E., Spokane, Washington, September 2, 1937. Published in Elec. Engg., August, 1937. 475