The use of level controlling devices in the radio-telephone service

This paper introduces the subject of speech level control as applied to radio-telephone service by presenting statistical data describing talker level variations and anticipated levels at the telephone central office. Because speech measurements are difficult to make, mention is made of speech to sine wave relationships that are convenient for system line-up. Next, maximum levels are established for the output of the controller and application to the wire-line or the radio transmitter. The operational characteristics of three available types of level controlling devices are discussed. These are: the Agamp and Vogad which were designed specifically for control of speech levels into radio transmitters; the clipper-limiter commonly used in radio broadcasting; and the Compandor which is familiar in telephone applications. Recordings were made of these devices in operation. Analysis of these recordings as related to the "ground rules" established in the text allowed conclusions to be drawn concerning the most advantageous use of each. In discussing the use of level controlling devices, it is necessary to determine the nature of the signals that are to be controlled. Where telephone facilities are to be used, consideration must be given to plant practices. These practices as well as the transmitter input requirements will establish the output level limits for the device. Having an idea of the input and output requirements and taking into account unusual noise and environmental conditions, the next step is to examine the characteristics, and cost of available units to determine the extent to which they meet the system application.