AMPLITUDE RANGE CONTROL 521 



the process of compressing the original wave. Sometimes an expander 

 is used at the receiving end to reduce the gain in the intervals between 

 the main signals even when no compressor is employed. This is an 

 example of using a range controller to correct defects in the medium. 



As is well known, the performance of a repeater is specified by such 

 characteristics as impedance, amplification, frequency band, noise, 

 and output carrying capacity. The performance of a non-linear device 

 involves some additional characteristics. The primary ones are (1) 

 the slope of the input-output curve, which tells how the range is 

 changed, (2) the dynamic operation, which tells the manner in which 

 the output varies with time following a given change in input, and (3) 

 the range, which tells the region over which the device exercises control. 



It may be helpful to imagine a range controller as an amplifier in 

 tandem with an adjustable attenuator, the loss of which may be 

 changed either instantly or slowly to follow in some predetermined 

 fashion changes in the signal. For simultaneous operation, this device 

 could put out a wave which is a simple function of the input, but if 

 the operation were delayed by a definite interval the device would be 

 required to respond in a complex fashion in accordance with a re- 

 collection of what had occurred in the signal during the delay period. 

 Such delayed adjustment would be very crude for intervals comparable 

 with the periods of fundamental speech frequencies. To obtain 

 practical regulation of the delayed type it is necessary to increase the 

 delay beyond this range and base the control upon the amplitudes of 

 the syllables. When the delay is increased to a point where it is 

 comparable with the syllabic periods its usefulness is again reduced. 



Part 1 — Control Ratio 

 Fundamental Characteristics 

 Figure 1 shows how waves may be altered by a device having a 

 given output-input characteristic, assuming the operation is instan- 

 taneous. As this figure is plotted on a db scale, only the stronger 

 portions of positive values of the wave are shown. A similar diagram 

 could be drawn for negative values. The output-input characteristic, 

 although a straight line in this kind of diagram, would of course be 

 parabola-like if plotted on a current or voltage basis. By selecting 

 points, such as A (or B), on the input wave and determining the rela- 

 tive outputs A" (or B"), the corresponding resultant wave is obtained. 

 In this case, the resultant has a flatter top than the original sine wave, 

 and this illustrates the capabilities of the device in increasing weak 

 signals with respect to the strong ones and also suggests that distortion 



