threshold on the PC76 U-Type Channel Compressor

hi,
i would assume this question must have been asked by now, so please excuse me, i didn't catch it.
it appears that of the two modes of compression on the prochannel comp, the default pc76 u-type compressor does not have a threshold control (the pc 4k s-type buss comp does).

is the threshold on the 76 fixed? if so, at what level?

thanks.

thanks jose,
when i read the description of it in the help files i missed this part that explains it:
 
Tip: The PC76 U-Type Channel Compressor does not have a dedicated threshold control, but instead has a fixed threshold level and uses the Input control to determine the relative threshold as well as the total amount of gain reduction. To set a specific amount of compression, first turn the Input and Output controls all the way down, adjust the Attack control in order to engage gain reduction, then finally adjust the Input control until the desired amount of gain reduction is achieved.

that's pretty interesting. i guess you don't really know at what level the compressor is engaging, just that it is and how much. still don't quite understand how the input level becomes the threshold though.

thanks humble, very informative.