You’ve created an ADSR with this line of code:
kadsr mxadsr iatt,idec,isus,irel ;mxadsr — Calculates the classical ADSR envelope using the expsegr mechanism.
Now all you need to do is use this variable to affect your filter cutoff. For example, if I wanted to use it to control a lowpass filter I might do something like this:
aOut moogladder aSignal, kadsr*10000, 1
The 10000 represents the cutoff frequency. This is required as madsr only moves between 0 and 1. You can take a look at this simple instrument:
It also uses ADSR envelopes to affect filters.