Discussion about the Korg PolySix synthesizer

Hi Folks,

Based on a previous post regarding frequency response of the synth's output, Johannes suggested that I check out the "compressor/expander" circuit on the KLM-368 effects board.  I totally agree that the circuit has an interesting effect on the sound of the synth.  I was hoping to figure out how it worked so I could better understand its purpose.

Below I show a schematic of this circuit along with some annotation and discussion of the individual elements:

http://synthhacker.blogspot.com/2013/02/mystery-circuit-polysix-post-effects-vca.html

Am I getting it right?  What is this thing actually doing?  Is it just a noise gate?

I'd love your thoughts.

Chip