this was used by the Game Blaster and SAM Coupé. it's pretty similar to the AY-3-8910, stereo sound, twice the channels and two envelopes, both of which are highly flexible. The envelopes work like this:
an instrument with envelope settings is placed on channel 2 or channel 5
an instrument that is used as an "envelope output", is placed on channel 3 or channel 6. You may want to disable wave output on the output channel.