The following is a sampling of text-books that are considered
standard. You can consult any one of them profitably. All
of them contain excellent end-of-chapter problems that should be worked
out if you really want to understand the subject thoroughly.
Textbooks:
Discrete-Time Signal Processing by Alan V. Oppenheim and Ronald W. Schafer, 3rd edition, 2010, Prentice Hall, Upper Saddle River, NJ.
Digital Signal Processing by John G. Proakis and Dimitris K. Manolakis, 4th edition, 2007, Prentice Hall, Upper Saddle River, NJ.
Digital Signal Processing by Sanjit Mitra, 4th edition, 2011, McGraw-Hill, New York, NY.