Frequency-selective dynamics act on one frequency band only when that band exceeds threshold

Some mix-balance problems live in the time and frequency domains at once: they occur only at certain frequencies and only at certain moments, so neither a static EQ (fixed, always-on) nor a full-band compressor (level-triggered but broadband) can fix them alone. Frequency-selective dynamics — multiband compression, dynamic EQ, a parallel dynamics return that is EQ’d, or side-chain EQ on an ordinary processor — apply a gain change to a specific frequency band only when the level in that band crosses threshold. Any dynamics processor can be made frequency-selective by placing it in a parallel setup with an equalized return, or by equalizing its side-chain. This targets a specific imbalance without touching the rest of the signal; side-chain EQ is also useful for refining gate triggering and for taming sibilance or pumping in heavy compression.

Examples

A dynamic-EQ band at ~4–6 kHz that cuts only when that band is loud de-esses on sibilants and harsh loud high notes while leaving normal vowels untouched — something static EQ or full-band compression cannot do alone.

Assessment

Define frequency-selective dynamics and explain why it solves problems that neither static EQ nor full-band compression can, giving a concrete de-essing example. Describe how to make an ordinary compressor frequency-selective.