[sdiy] More elegant trigger derivation?

[sbernardi at attbi.com]

I've been thinking about Harry's idea of deriving a 
trigger by differentiating the control voltage. So, I 
run the CV into a differentiator, which outputs a 
positive or negaitive going pulse depending on whether 
the the CV went up or down. Then this goes into a window 
comparator, because I don't care what the polarity is, I 
just want to indicate that it has changed. Say we set 
the window threshholds at +/- 100mV. 
I also want to generate a trigger when the gate goes 
high regardless of whether the CV changes (i.e., you 
could press the same note multiple times). So I run the 
gate into a positive edge detector and OR it with the 
window comparator output. Then I use this to trigger a 
oneshot such as a 555 to generate the actual trigger.
This can all be done with an op amp, a dual comparator, 
some logic gates, and a 555. Seems like a lot of parts - 
is there a simpler, more elegant way to do this?