DAFX: Digital Audio Effects, Second Edition

4.2 Dynamic Range Control

Dynamics processing is performed by amplifying devices where the gain is automatically controlled by the level of the input signal. We will discuss limiters, compressors, expanders and noise gates. A good introduction to the parameters of dynamics processing can be found in [Ear76, pp. 242–248].

Dynamics processing is based on an amplitude/level detection scheme sometimes called an envelope follower, a static curve to derive a gain factor from the result of the envelope follower, a smoothing filter to prevent too abrupt gain changes and a multiplier to weight the input signal (see Figure 4.7). Optionally, the input signal is delayed to compensate for any delay in the side chain, the lower path in Figure 4.7. Normally, the gain factor is derived from the input signal, but the side chain path can also be connected to another signal for controlling the gain factor of the input signal.

Figure 4.7 Block diagram of a dynamic range controller [Zöl05].

An example of a dynamic range controller's impact on a signal is shown in Figure 4.8. In this example, the dynamic range controller is a compressor: during periods of low signal level (first half of the shown input signal x(n)), the gain g(n) is set to 1, while for higher input levels (second half), the gain is decreased to reduce the signal's amplitude. Thus the difference in signal levels along time is reduced, ...