Variable and Constant Volume Operation in Telephone Communication System

The objective in voice communication circuit design is to deliver adequate acoustic power to the listener's ear in the presence of incidental circuit noise and thus permit satisfactory conversation between the talker and listener. The ranges of volumes applied to the circuit and the range received at the listener's ear in general are the same. The average received volume is essentially the average transmitted volume displaced by the net loss of the connecting circuit. The circuits between the talker and listener must carry the maximum volume without serious overloading. The minimum volume talker must be maintained at a high enough volume so that the listener will have an adequate signal-to-noise ratio to carry on a satisfactory conversation. The signal-to-noise for higher volume talkers will be greater by the difference in volume, which means the circuit is better than it needs to be for satisfactory conversation. It is suggested that the volume range be reduced by applying volume regulators to each long distance circuit. In addition, the peak-to-rms ratio of the signal is reduced by applying peak limiting. The average volume transmitted is raised to obtain the same overload expectancy. The increased signal power improves the signal-to-noise ratio. The improvement can be used to increase the signal-to-noise ratios in marginal circuits, or to reduce the cost of providing the service in new installations. It is shown that constant volume regulators applied to the present long haul plant will improve the poorer 10 per cent of the circuits by 15 dB or more.