Transient Shaping?

If anyone of you have tried using a transient shaper, you will know it's a bit different from a normal compressor, I'm interested in doing this in msp... I guess I should start out with an envelope follower, but, how do I differentiate between an attack and a release? And what exactly is it doing when it's puch-i-fying the attack, cutting off the release?

Here's a free transient shaper vst if you want to try the effect out:
http://www.digitalfishphones.com/main.php?item=2&subItem=4

I know I could just use it, however, it's sound quality is far from satisfactory...

Any ideas would help... cheers