Empirical Labs' DerrEsser brings multi-function dynamic filtering to the API 500 series module format. At its most basic, the DerrEsser is an effective de-esser. Employing a unique crossover technique the DerrEsser uses its Voltage Controlled Amp to reduce the volume of high or harsh high frequencies while maintaining musicality. Set your threshold, pick the frequency you want to control, and you're pretty much up and running. Of course, there are a variety of functions available depending on the settings, so plug in and see what DerrEsser can do for your vocals! Empirical Labs DerrEsser at a Glance: DS Mode HF Limit Highpass Lowpass DS Mode (Bypass Button in, all other buttons out). As a de-esser in the DS mode (HF Limit off), one can set the threshold to tame harsh S's (sibilants) that result from an overly bright singer or from EQ'ing to make a vocal sound aggressive and clear.