Although learning analog and digital filter design techniques is the first objective of this text, many readers may be interested in the use of C in the design and implementation of analog and digital filters. Therefore, supplementary material dealing with these programming issues is included in this and succeeding appendixes. All of the C code discussed in the first eight chapters of this text (and much more) is also included on the CD in the directory called \C_Code. The three short FFT functions in Chapter 9 are provided in the text.

The C programming language (and its successor C++) is a predominant force in engineering and computer science. In particular, C is the primary language used in digital filter design (with the possible exception of hardware-specific assembly language). C provides the combination of higher-level constructs while producing fast, compact executables. Other languages are available, and could be used in filter design, but C provides the best combination of efficiency and effectiveness. Several C language references are listed in Appendix A.

The primary data elements describing our filter will be used by a number of the design functions and therefore should be made available in a neat package. An array would be nice, but arrays require that all elements are of the same data type. Therefore the only reasonable choice is a structure.

We will store our filter data elements in a structure called Filt_Params. We can assume that we will need all of the filter specifications discussed in the...