"Discrete Time Signal Processing" by AlanOppenheim and RonaldSchafer (ISBN:0137549202).  One of the classic introductory textbooks into DigitalSignalProcessing.  Now in its second edition.  Excellent book.  Focuses on elementary DigitalSignalProcessing theory, including discrete signal transforms (DFT, Z-transform, FFT), digital filtering (FIR, IIR), sampling and reconstruction theory, etc.



-----

CategoryBook.