Dynamic range control

Abstract

A dynamic range controller consists of a multiplier 14 controlled by a side chain 18 comprising: a level detector 20, a log circuit 22, a threshold subtractor 24, a non-linear circuit 26, a slope multiplier 28, and an antilog circuit 30. The level detector (Fig. 4) comprises a peak detector with separate attack and decay time constants, in which the decay time constant is itself dependent upon the output of an r.m.s. detector. The slope and threshold values vary such that two or more different threshold/slope factor pairs are used for different sections of the signal amplitude so that the device provides different DRC functions (limiter, compressor, expander, or noise gate) for the different amplitude sections (Fig. 6). A smoothing recursive filter (Fig. 9) may be included between the antilog circuit 30 and the multiplier 14, and has a time constant which varies as to whether the detector is in the attack or the recovery mode, this mode determination being made with a degree of hysteresis. The response time constant of the filter is about one-third of that of the level detector 20. <IMAGE>

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