Envelope trigger circuit for guitar

[johns at oei.com]

     Can anyone recommend and/or point me to a good source (circuits or 
     methods) for making or designing a good, reliable, and easy to use 
     guitar envelope trigger?  I want to use my guitar to trigger an 
     envelope generator that will drive a VCF and VCA for guitar effects.
     
     In the past, I've casually tried to cook up cheap and dirty triggers 
     using an envelope follower and comparator but quickly found out that 
     it's not a simple job.  The input signal can vary so much that you 
     constantly need to ride the comparator trigger level to get a reliable 
     trigger.  I was hoping to find a more adaptive trigger that would be 
     "smart" about the trigger level.
     
     Thanks.
     
     John Speth - johns at oei.com