I recently did a swap-out of exhaust systems.  I used a Palm Pilot (Handera) to record the exhaust note with the stock exhaust, and with the Cobra exhaust.  Bike was positioned the same, and the Palm Pilot was placed on a piece of cardboard, to keep it consistent (and to keep from rattling against the ground).  

I think the mic auto-adjusted the record level, so don't try to figure-out which one is louder (hint: the Cobra is much louder).  Even so, I think you can hear the difference in pitch.  The stocker exhaust note has a whine and a hiss to it, while the Cobra is pretty much "Brrrrap": much lower pitch, more percussive, like someone beating a canvas curtain with a board.  Also, there are some "backfire"-like noises with the Cobra exhaust, whenever you roll-off the throttle, even if the bike is not moving.

Stock exhaust sample #1 (idle sound, then revved to 6500 rpm, then back to idle):  http://gs500.specialgreen.com/sounds/stocker-a.wav

Stock sample #2 (idle, revved to 6500, back to idle):  http://gs500.specialgreen.com/sounds/stocker-b.wav

Cobra F1r #1 (idle, not fully warmed-up yet, only revved to 5500, I think, then back to idle): http://gs500.specialgreen.com/sounds/cobra-f1r-a.wav

Cobra F1r #2 (idle, revved to 6500, then back to idle):  http://gs500.specialgreen.com/sounds/cobra-f1r-b.wav

yep thats what mine sounds like. (sort of) i think putting it on a computer dilutes the sound a little bit. but yea i like my F1R pipe. i wish i could put dual F1R's. i wonder what that sounds like. i know leveller has dual pipes but i dont know if they are stock or aftermarket. oh yeah sounds good