634 



BELL SYSTEM TECHNICAL JOURNAL 



curves can be obtained for w = 1, 4, 16, 64; furthermore, the fact that 

 the distribution for « > 64 is normal permits drawing the asymptote 

 for large values of n. The points read from Fig. 2 and replotted in 

 this way give the full lines shown in Fig. 3. 



In order to make practical use of these curves, it is necessary to 

 know what value of e corresponds to satisfactory performance of the 

 amplifier. Experiments have been conducted on a number of different 

 multi-channel amplifiers, each loaded by various numbers of active 

 channels all at the same volume. It has been found that for low 

 enough values of e, no audible disturbance is produced but that as e is 

 increased by increasing the load on the amplifier, the disturbance 

 falling into a channel not energized increases rapidly to a large value. 

 Two different amplifiers having the same computed load capacity 

 may show noticeable differences in performance in this respect when 

 subject to identical fixed loads of the type being considered, thus in- 

 dicating the influence of circuit design on the value of e. In general, 

 however, the allowable values of e measured for all of the amplifiers 

 that have been tested lie in a relatively narrow band on either side of 

 the curve for « = 0.001. The broken curve of Fig. 3 represents the 



-1^40 

 Occ 35 



O'^ 20 



'^l? 15 



O 



ceo 10 



>u. 



I 5 10 50 100 500 1000 



NUMBER OF ACTIVE CHANNELS fn) 



Fig. 3 — ^Overload voltage for n active channels. 



approximate upper limit of the observations, extrapolated parallel to 

 the € = 0.001 curve above n = 14. It is possible that some amplifiers 

 would overload even if operated in accordance with this curve, but for 

 the great majority of amplifiers of types thus far tested the operation 

 would be satisfactory, with perhaps a small margin. 



Multi-Channel Peak Factor 

 It is useful at this point to introduce the concept of "multi-channel 

 peak factor," which is defined as the limiting ratio cf the overload 



