dspGuru is a site dedicated to digital signal processing (DSP) designers. It has a good collection of resources for both beginners and seasoned users. Many open-source software titles can be freely downloaded, ranging from implementations of DSP algorithms to compilers and other software development tools. Five frequently asked questions lists cover some important DSP subjects, like finite and...

Dr. Steve Smith offers his book about digital signal processing (DSP) free, in its entirety, on this site. The DSP guide introduces the reader to the fundamentals, and then delves into digital filters, applications, and complex techniques. All 33 chapters can be downloaded individually or as a whole. The book is quite well written, with plenty of figures, graphs, and illustrations that accompany...