TASI Quality - Effect of Speech Detectors and Interpolation

TASI ( Time Assignment Speech interpolation) is a new component in the telephone system that can approximately double the message capacity of existing long submarine cables. With TASI many calls share the same facilities, each requiring an available channel only when speech is transmitted. In order to recognize that speech is being transmitted by the subscriber, a highly sensitive speech detector is required. To assign the speech to an idle channel and to connect the proper talker and listener at each end requires a rapid switching system. A description of the switching system and other related matters can be found in other sources. 1,2,3 This paper deals with: (a) the work carried out to select the parameters of a speech detector satisfactory for TASI operation and (b) the results of subjective tests made to determine the approximate effect of the type of speech clipping that can occur in a fully loaded TASI during busy traffic periods. Some speech is lost whenever the number of individuals talking or starting to talk in one direction on TASI circuits exceeds the number of available channels. The amount of lost speech must be kept small so that the transmission quality is not affected appreciably. On the average, less than 0.5 per cent of the total speech is lost due to interpolation, as long as the number of calls in progress is held to no more than twice 1455