Many people are put off using Digital Signal Processors (DSPs) by the thought of grappling with complex mathematical algorithms. In some situations a DSP offers the most cost-effective solution and in practice you don’t need to be Einstein to use them successfully. In this article we deal with a practical application and take a look at some of the background theory.Back in March 1998 we published a series of articles titled “Introduction to digital signal processing” which gave a good insight into the theory behind signal processing and used software routines running on a PC and its sound card to process signals. This article takes a different slant. Here we take a proprietary DSP chip (just a special form of high-speed processor using an instruction set that allows mathematical computations to be performed efficiently) and together with the author’s filter design software we build a practical filter circuit.