A few references and sites for sampling and MIDI
"Making Music with Samples" by Daniel Duffell , 2005.
This book is for the beginner who wishes to use sound samplers.
"Principals of Digital Audio" by Ken C. Pohlmann, 5th edition, 2005, Mac Graw Hill.
This book is meant audio engineers and covers tapes, DAT, Optical Discs, CDs, DVDs, desktop audio, internet audio, and digital radio and TV.
The lecture on this site covers the basics and is easy to read.
"A Practical Guide to MIDI in the Project Studio" by David Miles Huber, 2007.
This book covers a lot of material and also is easy to read.
The above website contains a good overview of various topics that include MIDI and sound sampling.
There is also an excellent discusion of problems with the FFT, the Fast Fourier Trransform.