Page "Linear filter" Paragraph 47

Before the advent of computer filter synthesis tools, graphical tools such as Bode plots and Nyquist plots were extensively used as design tools.

Even today, they are invaluable tools to understanding filter behavior.

Reference books had extensive plots of frequency response, phase response, group delay, and impulse response for various types of filters, of various orders.

They also contained tables of values showing how to implement such filters as RLC ladders-very useful when amplifying elements were expensive compared to passive components.

Such a ladder can also be designed to have minimal sensitivity to component variation a property hard to evaluate without computer tools.