Actually, I am looking for a generalized technique that will let me strip odd harmonics. I have an application that's using the boxcar as I described, both to indicate distortion level, and to subtract said distortion from a signal, but the odd harmonics have me stumped. I use one boxcar to take the signal, but of course it also passes the 2H, 3H, 4H... right on up, though past the 4th it's pretty well damped since it's an eight cap boxcar :) The second grabs the 2h and 4h components perfectly, but I have no simple answer for 3h and 5h. (Maybe I only need 3h, but you get the idea.)