[sdiy] Inverting an envelope?

[James Coplin]

What is the best (hopefully also easiest) way to invert an envelope?  I'm
finally getting around to racking up my SEMs and I wanted to add negative
versions of the two envelopes.  I don't want to invert the shape in the
positive voltage range but mirror it in the negative range. In other
words, instead of going from 0v to 10v and back to 0v, to go from 0v to
-10v back to 0v.  Thoughts?

James R. Coplin