http://eceweb1.rutgers.edu/~orfanidi/intro2sp/
it has
- explanations
- equations
- FIR block-diagrams of filters
- code for the filters
- etc.
lots of presentations of the information in one. the thing that finally helped me start understanding intermediate DSP and filled in gaps in the basics. You should read this if you want to try doing DSP and don't know where to start. Or if you want a DSP filter cookbook for a lot of common filters. Free online but I bought a physical copy from their print on demand shop a couple years ago and it's been great.