AMPLITUDE CHARACTERISTICS OF TELEPHONIC SIGNALS 547 



range includes a region within which compression at a syllabic rate can 

 take place; at other inputs the device is a linear transducer. Its 

 connecting diagram and time functions are the same as those shown in 

 Fig. 5 except that the control circuit contains a limiting device, so that 

 compression takes place in only a portion of its input range, analogous 

 to the action of the limited range expandor of Fig. 6. As a special case 

 the limited range compressor may have no linear range above its 

 compression range, thus becoming one type of peak limiter. 



6. The peak limiter (Fig. 8) is a device whose gain will be quickly 

 reduced and slowly restored when the instantaneous peak power of the 

 input exceeds a predetermined value. The amount of gain reduction is 

 a function of the peak amplitude, and in practice is usually intended to 

 be small to prevent material reduction of the range of intensity of the 

 signal. 



7. The peak chopper (Fig. 9) is a device which prevents transmission 

 of peak amplitudes exceeding a critical amount, an essential charac- 

 teristic being that the loss it inserts is completely determined by the 

 instantaneous voltage of the signal. That is, its operating and 

 releasing times are substantially equal to zero. 



8. The crosstalk suppressor (Fig. 10) is a device which normally 

 presents a prescribed loss to transmission, which loss is removed 

 rapidly when the input amplitude exceeds a certain threshold and is 

 reinserted at a definite time after the input is removed. It reduces low 

 amplitude unwanted currents such as crosstalk but does not affect 

 amplitudes in the useful signal voltage range. This device differs from 

 the limited range expandor in that the time during which the low loss 

 condition is maintained is considerably greater, so the transition from 

 one gain to the other occurs less frequently. 



9. A rooter is an instantaneous compressor. Such a circuit can be 

 made to produce an output whose instantaneous voltage is, for example, 

 the square root or some similar function of the instantaneous voltage 

 applied to the input. An inverse rooter is an instantaneous expandor 

 whose characteristic is complementary to that of the rooter. A 

 combination of rooter and inverse rooter will reduce the load require- 

 ments on a transmission system between the two units but requires 

 that it transmit a wider band of frequencies than that for the original 

 signal, and that it be essentially free from phase distortion. This does 

 not seem to be an attractive arrangement from a commercial viewpoint 

 and is included here simply as an illustration of one of the possible 

 modifications of signal energy. It is not shown" in the group of 

 diagrams. 



