DeHiss has just one control, Threshold. Sounds below this threshold will be de-hissed.
It’s not like a simple EQ: the algorithm’s doing freaky things relating to the mean level of samples, but for all practical purposes it acts like a gate that can clamp down brutally on high-frequency noise. The plugin was designed to cope with a tacky little prosumer USB mic pre that I won’t mention here, except to say it is the MXL Mic Mate and its claims of having a “Fully balanced, low-noise analog front end” are BAAAHAHAHAHA… erm, possibly somewhat exaggerated. But for $40 I suppose it’s all right (you can pay that much for a really high quality JACK…)
DeHiss maybe isn’t very sophisticated, but it sure as heck clamps down on noise. Most of what it’s doing codewise is dragging musical tone out of a pit of raw hiss. It’s a pretty good sounding lowpass in some ways and could be used as one if you just crank the threshold to full. I’ve tried it on basses and guitars, and it can produce pops and ticks from the threshold engaging/disengaging but it can also work pretty well as a gate, or as purely a lowpass. Since the method of clamping noise is so unusual, it produces a distinctive tone when used in place of a traditional lowpass, with a bit more muscle to it.
DeHiss declares one sample of latency.