AMPLITUDE RANGE CONTROL 535 



input range of the device, and also from the range over which control 

 is exercised. 



This control range may be defined as the difference between the 

 maximum and minimum values of an applied wave over which a 

 device is designed to function in a specific non-linear manner. It is 

 usually expressed in db, and may apply to any measure of the applied 

 signal, such as instantaneous voltage, rms steady-state sine waves, or 

 a dynamic measure such as volume. The values dividing the con- 

 trolled range from the uncontrolled ranges may be referred to as the 

 "control points." 



Certain advantages in some cases have been found from restricting 

 the control range. This is accomplished by placing one or both of the 

 control points inside the useful amplitude range. The position of the 

 control point may be moved arbitrarily over a wide range by putting 

 an ordinary repeater (or attenuator) in tandem with the range con- 

 troller. A given amount of compression at the high amplitude end of 

 the range gives a real signal-to-noise advantage for a much greater 

 proportion of applied e.m.f.'s than the same amount of compression 

 at the low end of the range. In either case the distortion would be less 

 than that of a full range compressor. When expanders with limited 

 range are used, they are subject to the limitation that variations in the 

 medium are increased, but to a lesser extent than full range expandors. 



Part 4 — Classification of Range Controllers — 

 Secondary Characteristics 



Table I, page 536, suggests how the conceptions of control ratio, 

 time actions and range already discussed might be employed to dis- 

 tinguish a variety of devices. In cases where more than one device 

 is covered by a given control ratio and time action the distinction is 

 that the ranges are different. The names of devices used in this table 

 are those which have been used in the past to distinguish the devices 

 one from another. 



Nomenclature 



Using the above conceptions of the three primary characteristics, 

 it has been found possible to devise a notation to distinguish all the 

 known devices in this field. As an example of how this proposed 

 system of nomenclature would be applied. Table II, page 537, gives 

 three columns. Column 1 sets forth the arbitrary names that have 

 been used in the past to distinguish certain devices which have come 

 into use. Column 2 gives descriptive names which specify the three 

 fundamental characteristics. In column 3 each device is named by 

 three symbols defining the three fundamental characteristics, and a 



