Any introductory text on SISO (single input/single output) control theory will be a good start, since the same underlying tools are used for signal processing a

Any introductory text on SISO (single input/single output) control theory will be a good start, since the same underlying tools are used for signal processing as well as active control systems. The Wikibook on control systems is OK, and will at least get you a feel for some of the mathematics. Modern Control Systems by Dorf and Bishop is a great SISO textbook. Modern Control Theory by Brogan is a great MIMO (multi-input/multi-output) text, too. For just noodling and doodling around, the functions 'tf', 'ss', 'bode', 'freqz', 'butter', 'tf2sos', 'besself', and 'c2d' are a decent start. https://ccrma.stanford.edu/~jos/filters/filters.html https://ccrma.stanford.edu/~jos/filters/filters.html and http://dspguide.com/ http://dspguide.com/ are great online references for digital signal processing, and you'll find that many of the underlying mathematical tools for discrete-time analysis carry over into the continuous domain, too.