A recurring problem in ac filter circuit design, is the calculation of attenuation at a particular frequency or conversely the calculation of a frequency given the attenuation. In addition related calculations deal with estimations of time constants and filter parameters such as resistance and capacitance. These calculations play a crucial role in the design of anti-aliasing filters, low pass filters, phase lock loops etc. A paper published recently by the techteam at Signal Processing Group Inc, documents these calculations and provides examples for interested readers, cookbook fashion. The paper is located at http://www.signalpro.biz >engineer’s corner.