extracting data (peaks) from signal.

So i have a wav file of me playing my guitar. I have smoothed it, and computed the derivative of it so i can see the 'attack point' of each note if you will.

http://oi46.tinypic.com/30shcmt.jpg

^There is my plot of the smooth signal, the red points are the data i want to aquire (x and y value is preferable). How would i do this, I assume the find peak function, some sort of threshold?

if you zoom in on the graph:

http://oi48.tinypic.com/33nz1bs.jpg

You see why its a little more complicated. It doesnt have to be 100% accurate but i need to roughly know when in relation to time each new note is hit (approx).

Any ideas HUGELY welcomed. and if there is anything i can do for you in return just let me know :D

Thanks

[Carlos]

I've had the same problem, but in a much easier case. Have you tried something like?

[pks,locs]=findpeaks(data,'minpeakdistance',5e4);

In your case minpeakdistance should have a value like 5e4.

[David Mehr]

Believe me i have tried this, using a boundary like this works sometimes but the drastic changes in notes take place over 3 or 4 elements, i was thinking of maybe implementing something that looks at the difference in height of several elements?

Bit of a lost cause really to try and find something so general for such obscure data.