Hello All. Let me explane what I am trying to achive and what I problems I have hit. I am trying to make a device that will allow me to plug a mic into, and a pot that will allow me to sweep through the ENTIRE audio frequency range at a bandwidth of 500hz. Here is an ilistration of what I meen: My first attempt was to do it all analog. Using a simple RC Filter set up as a bandpass and using pots. However the accuracy of the components meant that I couldnt have enough control over the values and I found the bandwidth would fluctuate. So Im now attempting to do it digitaly with an Arduino. I have managed to input audio from a mic that passes through a preamp. I had to directly adjust regestry values to allow a fast enough frequency for the ADC and the PWM. The output is fitered to remove the fast PWM carrier frequency. A lot of reading about FFT has helped understand it. Ive looked at demos of spectrum analysers and had the idea that: With spectrum analysers you have many bins of diferent groups of frequencys and you output the amplitude of each bin, well how about having 3 bins, 2 bins get discarded (the two bins below and above the accepted 500Hz bandwidth) and the 3rd bin is what we want and output the contents of that bin. Can I then just adjust the values of the bin's boundries. Does this sound feasable? Thanks, Phil.