Amplitude Range Control

TN a "non-linear" transducer, the o u t p u t power is not proportional to the input power. Consequently, the ratio of m a x i m u m to m i n i m u m power at the o u t p u t differs from that at the input. B u t the ratio of m a x i m u m to m i n i m u m power is an expression of amplitude range. A device designed to alter this ratio m a y be called a range controller. In telephony the term range controller includes m a n y devices 1 having specific names, such as limiters, volume control devices, range reducers, compressors, vogads, expandors, etc. These devices have m a n y properties in common with telephone repeaters, and a repeater m a y be considered as a special case in which any non-linearity which m a y exist between the o u t p u t and i n p u t is unintentional. The purpose of one type of range controller is to reduce the range of significant intensities of signals applied to a telephone circuit so as to ease the requirements of the transmission medium with respect to overloading and noise interference. Such a device is placed at the transmitting end of the circuit. W h e n the range is compressed at the sending end of the circuit it m a y sometimes be desirable to expand it at the receiving end to the original range. This is done with a device having, in general, the same dynamic characteristic as the compressing device, but a range change which is complementary. The purpose of the expandor is to reduce the noise heard by the listener as well as to compensate for whatever characteristic signal modification occurred in 1