ABSTRACT
The EQ/tone control theory is the most diffi cult of all the effects to explain in a simple way. These effects are based on DSP fi lter theory which involves complex algebra, that is, the algebra of complex numbers. Complex numbers contain real and imaginary parts. There are two basic ways to explain basic DSP theory. The fi rst is intuitive and involves no complex math but requires some bookkeeping and can be tedious. The second method uses complex algebra to solve the problem. We’ll start with the intuitive method, and then (optionally, if you desire) make the leap into complex math. Don’t worry-we don’t want to get mired down in theory and forget the fun part, which is making audio effects. If you skip the second part, you will still be able to code EQ and tone control plug-ins, but you will better understand where the equations come from if you know a little theory too. The transfer functions you will learn along the way will reappear in many effects algorithms.
