"Back in 2001, while designing the Quartet Tube Recording Channel, I decided that it needed a de-esser as one of the four elements. Though I'd never bothered to look into how they operate – much less built one myself – I blindly went off and started tinkering. Attempts at de-essing via the sidechain of a compressor to pull down the amplitude of the "s" worked ok, but did not sound natural to my ears or leave enough of the "s" to make it recognizable. <br/><br/>
So, I decided to try using the fast opto cell from the OCL-2 as part of a triggerable LC notch filter, which covers a specific range of fundamental frequency where the "s" is most annoying. By varying the depth and the bandwidth of the notch, I discovered that there is a sweet spot  where the "s" is recognizable, but not splashy. Because the sweet spot is often singer-dependent, I added a depth control to allow the user to determine how much of the "s" to leave in. Owners of the Quartet often praised the de-esser, and found it effective in many other applications, including removing finger squeaks in acoustic guitar tracks, and "wisp" sounds on electic bass. <br/><br/>
Ten years (and many requests) later, I've been convinced to put out the de-esser in a stand-alone 500 series card. It is identical to the one in the Quartet, but implemeted around a unity-gain class A solid-state line stage."<br/><br/>
Greg Gualtieri<br/>
<em>Designer</em><br/><br/>
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		Don’t forget to check out 
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