Guitar String Replucks I'm analyzing guitar string plucks and sustains.  I'm having good success with auto correlation using FFT's.  Now I'd like to detect plucks while the string is still vibrating.  Since I already am periodically taking FFT's to find the pitch, I thought maybe I can take advantage of the fft results and look for changes that might indicate a repluck.  Do I simply add up the bins for some kind of power measurement?

Any ideas?
A pluck might produce significantly more broadband noise than a free string.  An FFT of such noise would show more relative energy outside of all the FFT result bins that are related to (F0 or overtones of) a single pitch.  

Also, a free string has a more predictable decay rate in any FFT magnitudes related to the pitch across successive offset FFT frames windowing the sound data.  A sudden change from this decay rate (a stop or a big increase) might infer a disturbance, such as a pluck.