Masking of Crosstalk by Speech and Noise

l.i General Background In the process of transmitting speech over telephone channels, a portion of the speech energy occasionally gets transferred from one channel to another. This transferred energy is technically referred to as crosstalk. The presence of crosstalk in telephone circuits is objectionable for two main reasons, (i) Its presence may indicate to customers that they are receiving a telephone service which does not protect their * T h e material of this paper was presented before the 74th Meeting of the Acoustical Society of America, 16 November 1967; "Masking of Crosstalk by Speech and Noise," J. Acoust. Soc. Am,. Ifi, 1198(A)-1967. 561 562 THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1970 own privacy. (ii) It may interfere with speech transmission and thus degrade the circuit quality. Since the Bell System strives to maintain a certain standard of transmission quality and provide privacy to the customers, it is concerned with controlling all sources of circuit degradation, including crosstalk interference. Designing the telephone plant to guarantee complete absence of energy transfer between channels is not economically feasible. Therefore, to guarantee privacy and to maintain a certain standard of transmission quality, the usual engineering strategy (which is maintained with a high degree of probability) is to limit the crosstalk energy below a threshold such that (i) it is not intelligible and (ii) it does not subjectively degrade the circuit quality. This threshold is experimentally determined by subjective testing, using simulated telephone connections.