I've decided to task myself with building a large scale spectrum analyser to get me back into electronics as I figure it will use the most common base components (transistors and op-amps) and will jog my memory on what does what. I know there are a few guides around, but they either give the circuit diagram with no explanation of what's going on, or talk about things that I've long since forgotten. I'm trying to piece together how to build this circuit myself rather than follow a suck-eggs-follow-and-learn-nothing style guide, and trying to re-learn what and how each component works. Right now I've figured that I should be looking to split the output signal into different frequencies and then indicating the volume of each frequency separately. So I plan on using low and high pass filters (band pass?) to split the frequencies into manageable chunks. For getting the volume display I want to do it in roughly 3db intervals as this is roughly double the sound intensity (not entirely sure how I'm going to achieve this), then it's a case of somehow triggering the LED when a certain voltage (volume) is achieved. Finally, rather than triggering a single LED, I want it to set off a large cluster of LEDs (as this is going to be a rather large display), so I'll need some way of triggering the cluster. So my questions here are mainly: Am I going the right way about the project as a whole, or am I in totally the wrong direction? Should I be looking at another method to split the frequencies, or is a low pass plus high pass filter good enough for the job? For the actual volume display, how would I discern the ~3db different? Would I need to double the voltage required to trigger the LEDs (as this I believe would be the double intensity that an ~3db increase would incur)? For triggering the LED section of the circuit, should I be looking at op-amps or transistors? Lighting a large cluster of LEDs from what I assume to be a low voltage output, should I be looking at using a transistor as a switch? Finally, can anyone recommend some good online reading material while I try and source my old college paperwork (it's been a fair few years, but I know it's here somewhere...)? Hopefully I've not just reduced you to a shaking wreck with my obvious obliviousness, and thanks in advance to anyone who helps!