Now explain the circuit in YOUR OWN WORDS. Copying and pasting from Wikipedia isn't understanding - if it were, there'd be no end of experts on everything everywhere.
You're just avoiding a very simple question - do you know how shit works? It's not indicating much confidence, and only driving my point further. Anyone can make their own multiband compressor by splitting a track with EQs, compressing the split tracks, and then recombining. Do you know what the fuck heterodyne actually means? Hell, if you could regurgitate basic trigonometry to back yourself up (NOT from Wikipedia!) I'd be damn impressed.
The original poster wanted to learn more about plugin designing, not have one magical black box replaced with a bafgiquintizillion other magical black boxes. That involves more than copying and pasting. It's not hard - hell, some funny-looking eccentric jackass with a little too much time on his hands figured it out, it can't be that hard - but the sooner people give up the mindset of 'well, I understand things better because I have a lot of little things I don't understand instead of a few big ones' the better.
Jeff