[sdiy] Help with lm339

[J C]

I am trying to use a lm339 comparitor to determine when an ADSR signal
reaches the sustain level.  What I want to do is add a small voltage
to the sustain level voltage so that the comparator fires just above
when the envelope reaches it (if I don't do this, it just waffles
around when the two voltages are equal ie:when the envelope is
sustaining).  Is there a simple way to do this (without adding a
summing opamp)?