The Envelope is not at all like the CS80 envelope...I will explain
The CS80 has 2 level controls for EG Depth of the 2 filters....
IL 0 to -5 and
AL 0 to +5
When you set your HPF and LPF filters, you are doing it at Sustain level...
This allows you to set your filter as you would want to hear it if the note was held down...
IL is and AL is = to the sustain level if set to 0, thus no envelope is heard...
If you raise the "Attack Level" to +5 the attack will start at sustain level, and rise based on attack time to the decay point, where decay or release time will return to the sustain level ... this is an eg that starts and ends at sustain level...
If you Zero the "AL" and move the "Initial Level" to -5 , the attack will start below the sustain level and rise to the sustain level and then release to the lower level...
This is now acting like the Arp AR envelope....
If you +5 the AL and -5 the IL, the attack starts at a lower than sustain to a higher than sustain at the decay point which then decays to the sustain point, and upon release returns to the lower than sustain level creating an ADSR envelope...but keep in mind, the sustain level is fixed to the HPF and LPF cuttoffs....
The reason they built it like this was for speed in building patches... you dont need to go back and forth between the 2 touchy cutoff controllers and the EG levels to set your sustain levels..
with the Current filter EG your sustain level will change if you adjust the eg amount ...
so you wont be able to do the (-5 IL) AR type EG or the (+5 AL) releases at sustain levels EG