...here's an attempt using three KarmaFX Synth instances:http://www.youtube.com/watch?v=hH8Im2oo5qU
Not sure what you mean by "track off input" (?), but a standard "analog" envelope controlled VCF is simply a matter of hooking up an ADSR modulator to control cutoff on a Filter module. But if you're looking for envelope _tracking_ then the you need to hookup and Input module and route it into an EnvFollow module.