Examples of DeEssers:
This one is from Waves.
These can be set to trigger on frequencies in the high range where these “sss”/harsh guitar string bite/cymbal crashes, etc… sounds reside.
It’s focus filter was set around 3kHz.
The DeEsser will turn down all sounds that get louder than the threshold.
Don’t over do it. More than 6-10dB reduction, in some cases, can make people sound like they have a lisp!!!