According to Textbook Revolution, "This is the free online edition of one of Amazon’s bestselling DSP textbooks. In 640 pages over 33 chapters, it covers the topic very thoroughly. Well-reviewed and clearly written, the book keeps equations to a minimum and has over 500 graphs and charts to spice things up. Nice bonuses include problem sets and free software to go along with the book. Smith gets bonus points from TBR for using the word “revolution” in his intro (see below). The book has standard copyright with a number of exceptions. You can print one copy, you can download the whole thing, professors can distribute one chapter in class, etc. See the site for all the details." And from the website itself: "Digital Signal Processing is one of the most powerful technologies that will shape science and engineering in the twenty-first century. Revolutionary changes have already been made in a broad range of fields: communications, medical imaging, radar & sonar, high fidelity music reproduction, and oil prospecting, to name just a few. Each of these areas has developed a deep DSP technology, with its own algorithms, mathematics, and specialized techniques. This combination of breath and depth makes it impossible for any one individual to master all of the DSP technology that has been developed. DSP education involves two tasks: learning general concepts that apply to the field as a whole, and learning specialized techniques for your particular area of interest. This chapter starts our journey into the world of Digital Signal Processing by describing the dramatic effect that DSP has made in several diverse fields. The revolution has begun."