Ableton Live 8 Compressor
Ableton updated the compressor in Live 9 adding a new user interface and changing the guts to create a very powerful and awesome new compressor.
With one exception Ableton removed the old model Types and Envelope Follower Modes. A lot of people have come to love Ableton lives old compressor.
FF1 model is great for fast side chaining with no clicks. A Feedback/Opto combo was great for smooth and lush vocal compression or to compress a drum buss.
The Live 9 compressor does not have these features but never fear, you can load the old compressor into Live 9 and 10.
It will have the really useful new graphical interface of the Live 9 compressor but all the features of the old Ableton Live compressor from Live 8.