The subject of digital filter design is enormous--much larger than we can hope to address in this book. However, a surprisingly large number of applications can be addressed using small filter sections which are easily designed by hand, as exemplified in Appendix B. This appendix describes some of the ``classic'' methods for IIR filter design based on the bilinear transformation of prototype analog filters, followed by the simple but powerful weighted equation error method for general purpose IIR design. For further information on digital filter design, see the documentation for the Matlab Toolboxes for Signal Processing and Filter Design, and/or [64,68,60,78].