. The Bell System technical journal . omething like the rectified envelope. Figure 6 shows the impressions of the wave of Fig. 3a, using fourdifferent values of time constant RC as compared to P, the period *of the envelope. Figure 7 shows smoothed summation curves of theimpressions of Fig. 6 formed during the time P/2. Comparing thiswith Fig. 4, it is evident that the bunching effect for the distributionof impressions is largely between those for the rectified instantaneousand envelope curves. For the longer time constants, , weak im-pressions, this is not the case for the weaker
. The Bell System technical journal . omething like the rectified envelope. Figure 6 shows the impressions of the wave of Fig. 3a, using fourdifferent values of time constant RC as compared to P, the period *of the envelope. Figure 7 shows smoothed summation curves of theimpressions of Fig. 6 formed during the time P/2. Comparing thiswith Fig. 4, it is evident that the bunching effect for the distributionof impressions is largely between those for the rectified instantaneousand envelope curves. For the longer time constants, , weak im-pressions, this is not the case for the weaker * This is twice the duration of Fig. 3, since only half a cycle is illustrated. It isassumed that C is completely discharged at the time this wave is applied. In prac-tice, the rectifier impedance varies with the applied so that the results arenot as simple as in this illustration. In general, the time actions are different de-pending on whether the applied is increasing or decreasing. 530 BELL SYSTEM TECHNICAL JOURNAL. IMPRESSION AMPLITUDE RANGE CONTROL 531 Referring again to Fig. 6, it will be seen that for the two smallervalues of RCJP the impression curves are composed of (1) the envelopefrequency, (2) double the fundamental frequency, and (3) a small delaywhich can often be neglected. An approximation to envelope com-pression is therefore possible by choosing RC/P to be in the properrange, , .0025 to .025, and making the output vary as a root or powerot the impressions thus formed. Figure 8 shows the result of compressing the wave of Fig. 3a byusing the impressions of Fig. 6 to determine the amplification. It was 0 RC _P ^ ^ «=-^^---]7 ^ ^^ -^ - // ^^^ .^r X - / ,4 / J 1/ / / / / 60 0 10 20 30 40 50 60 70 80 90 100 PER CENT OF TIME IMPRESSION IS EQUAL TO OR LESS THAN IMPRESSION SHOWN Fig. 7—The amplitude ranges of the impressions shown in Fig. 6 are buncheddifferently, depending on the time constant. A volume measurement means thata given impression i
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