<From: Sam Ismail &lt;dastar(a)wco.com&gt; <Now contrast this with an analog filter, which performs a singular <function based on the laws of physics. No instructions, no codes, no <processing unit. Therein lies the distinction. The explanations of physics is based on the core of mathmatics. That's one way to look at it. Consider it from the perspective of a mathmatics view. Signal goes in FNC(x) is performed on it and signal comes out. FNC(x) can be performed using a DSP or analog circuits Computing is a process of calculation. Analogue functions perform calculation vastly different than the digital forms it does not negate the calculation performed. If this wasn't true digial signal processing would not be possible. I still have the Popular Electronics article that simulates the bounce of a ball in analogue form using opamps while displaying it graphically on a scope. Yes the ball would even flatten at the bottom of the bounce. Years later I would write a program to do the same, the mathmatics were unchanged as where the physics. The analogue form was faster at showing how small changes had an effect, it could be real time. The digital form allowed me to express those as floatingpoint numbers. Even on a PDP11 at the time, it would never approach real time. Allison