. The Bell System technical journal . ^ ^ -^ -^ ^ •- r^^ B_, ■- - —- —* ^^ ^- ^ - A - -^ -- ^^ C -^ -• ■ ^ — 5 10 20 30 50 100 200 300 500 1000 NUMBER OF CHANNELS IN SYSTEM (N) Fig. 6—Equivalent volume for systems of N channels. 638 BELL SYSTEM TECHNICAL JOURNAL case where the volume of each of the active channels is controlled soas to be db below reference volume. The choice of this particularvolume is purely arbitrary, but it corresponds to the average power ofthe single talker volume distribution. The equivalent volumes given by curve A of Fig. 6 are a measureof the average power of th
. The Bell System technical journal . ^ ^ -^ -^ ^ •- r^^ B_, ■- - —- —* ^^ ^- ^ - A - -^ -- ^^ C -^ -• ■ ^ — 5 10 20 30 50 100 200 300 500 1000 NUMBER OF CHANNELS IN SYSTEM (N) Fig. 6—Equivalent volume for systems of N channels. 638 BELL SYSTEM TECHNICAL JOURNAL case where the volume of each of the active channels is controlled soas to be db below reference volume. The choice of this particularvolume is purely arbitrary, but it corresponds to the average power ofthe single talker volume distribution. The equivalent volumes given by curve A of Fig. 6 are a measureof the average power of the N channels, as computed by means ofequation (2). To determine the required instantaneous load capacityof the system, the average power must be corrected by the multi-channel peak factor which is read directly from Fig. 4, using for thenumber of active channels the values read from Fig. 5. For design purposes, it is more convenient to use the rms powerof the single frequency test tone whose peak value represents the. 5 10 50 100 500 1000 NUMBER OF CHANNELS IN SYSTEM (n) Fig. 7—Load capacity for systems of N channels. instantaneous load capacity. As the ratio of the peak to rms power ofa single frequency tone is 3 db, this test power is obtained by subtract-ing 3 db from the instantaneous load capacity. This required test-tone capacity is plotted as a function of N in curve A of Fig. 7, whichgives the output capacity required for an iV-channel system withvolume control as specified above. Uncontrolled Volumes For systems in which volume control is not used, the application of this procedure becomes more involved. To study this more general case, it is convenient first to interchange the conditions of the preceding section, letting the number of active channels be fixed at any value n LOAD RATING THEORY 639 and examining how the distribution curve of equivalent volume maybe obtained for this fixed number of channels. The relation betweenvolume and average speec
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