As touched upon previously, some dynamics processors have filtering or EQ in their sidechain, causing them to react more (or less) to certain frequencies. This is known as frequency-conscious dynamics processing, and the most common form is the de-esser, a tool used to control high-frequency sibilance in vocals. However, the same concept is also found in general purpose frequency-conscious dynamics and dynamic EQs. .
For a de-esser or frequency-conscious compressor, the filtered sidechain signal feeds (aka keys) the detector, so gain reduction is caused predominantly by the focus frequencies. In the case of a dynamic EQ, the sidechain keys the gain of a filter circuit, and so it’s basically a specialised EQ and we therefore won’t be covering it in this article as we want to focus on the core dynamics processors (note, however, that some de-essers do use this technique of dynamically controlling EQ filters).
In a basic de-esser, ‘ess’ sounds will trigger broadband (full frequency) compression, which will cause the whole signal to be reduced in level during the sibilant parts. However, by using a filter circuit to split the signal, it is possible to process just the relevant frequency range, leaving the rest unscathed, and some de-essers offer this functionality – in essence, what you’re seeing is a basic multiband dynamics processor (which we’ll cover in detail on page 48).
“In essence, what you’re seeing is a basic multiband dynamics processor”