Empirical Labs EL500 Plus 1U Horizontal Racks Configuration. The very first entry by ELI into the 500 series format, the DerrEsser is a multi function dynamic filtering unit. Readily available in vertical or horizontal versions. An ideal fit for our EL500 powered shelf. In its fundamental “DS” mode, it is an effective, level insensitive “de-esser” – an unit that will certainly adjust the high frequency gain on extremely trebly or spiky vocals or additional sources in an exceptionally musical manner. Nevertheless, unlike additional de-essers, the device permits multiple use of its powerful circuitry.