PC4K Compressor HPF?

Hello,

Can someone enlighten me exactly what this red knob does?

Thank You,
Adam

TS

"High Pass.

Applies a High Pass filter to the sidechain input. The valid range is OFF to 2 kHz."

 

X2 Reference Guide, page 980

Thanks for the reply.  I did read that, but don't totally understand what it means.   What is happening when its all the way to the right (Default State) and then all the way to the left?   
 
I notice in a kick/bass situation, more gain reduction is applied by turning it to the left, but I just don't understand why.  
 
Sorry if it's a newbie question.
 
Adam

Keni
A high pass filter does exactly that... It rolls off low end and allows the highs to pass... The knob adjusts the chosen frequency to use as the roll off point and will then reduce the gain from that frequency down at its pre-defined ratio...

Keni

So if I move it to the left, it only compresses based on the highs?   Is it compressing only those frequencies?  I guess im not understanding the concept of what is coming in, what is being used to compress and what frequencies it is compressing.
 
I understand what an HPF is, but not how it relates to this compressor.

Thanks,
Adam

one of the intricacies of a compressor is that the input signal going into it affects how it works!
bass frequencies are stronger than are high frequencies-- that's why we hear thunder from miles away but not the clap of the lightning-- and therefore trigger the compressor to work harder, and can result in squashing a mix to death.  
a sidechain hipass on a compressor helps compensate for this and will allow the bass frequencies to go through untouched, while the rest of the frequencies above gets compression. in dance music, this is key, because the kick/bass don't always need to be compressed in a mix; they need to stand out.
starting from OFF-- meaning NO sidechaining compression is happening, the whole mix will be compressed.
turning the knob fully the other way will gradually raise the cutoff frequency for what gets compressed.
 
in the sonitus compressor, you can sidechain in a different way by putting the compressor on a sustaining pad or string sound. then you send a kick into the sidechain input and it will dip the strings down in volume every time it "hears" the kick drum. also used heavily in dance music for that pumping/throbbing sound.

Great explanation from Scook and Cliffr. Thank you! 

The way I read the reference guide, the HP filter is a filter for an external input to the compressors side chain.

Which would make soundsub explanation of a typical use of a side chain FXs correct.