I was thinking about 3-tone stacks. I know about high and lowpass filters. However, what i don't understand is how you can make a filter for a particular frequency. Perhaps you could combine two filters (high and low pass) centred around the freq. in question, but there mut be an easier way than this.
Any help appreciated.
Look at the article on "simple easy parametric EQ" at Geofex. It's all explained there with some working examples. http://www.geofex.com/Article_Folders/EQs/paramet.htm