Hi, all I've been reading these forums for a while, and now that I have a question, I've finally decided to join. The question I have is school-related, but not really direct coursework since it's very open-ended. I am part of a group (in electronics class) that is building an LED bar-graph based spectrum analyzer. The concept is pretty simple - a bunch of filters each of which selects a frequency, and an LED bar graph circuit that lights up according to the amplitude of each filter's output. We are currently trying to figure out what kind of filter to use for this and how to quantify our specifications. Since op amps a re a point of great emphasis in the course, we came to the decision to use an active filter (Sallen-Key or something similar). Does anyone have any general advice on what kind of filters to use for such project? Should we use a butterworth bandpass filter for every band with a good amount of bandwidth, or is it better to go for hi-q filters and label each bar graph in terms of its center frequency? Also, how tolerant should we be of roll-off for this application? Would something like 40-60 dB per decade be OK. PS. If i make myself sound ignorant that's because I am. No one in the group has any real signal processing or filter-design experience. We have not been formally introduced to active filters, and the point of the project is to do something not necessarily within the official scope of the course.