Here’s a plug-in that I’ve put together based on the above description.
I’ve only done basic testing, and don’t have a good selection of sibilant speech recordings to test with, but from limited tests it seems to work reasonably, though a bit fiddly to set up. Previewing the “Residual” (the “S’s”) helps, as does checking the frequency response in Plot Spectrum.
I’ve commented just about everything so that you can see what it’s doing and how, so hopefully it will be a useful starting point for your own plug-in. de-esser.ny (2.87 KB)