Frequency-conscious dynamics
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).