This is my idea for a guitar tone control... but I would have alot better control with an eprom set to fire 65000 different capacitances....
so I want to build a digital version with more lights!
Using a simple op-amp you can make a filter (or multiple filters) for the bands you want and the LED is usually a 'column' that indicates the level of signal.
For single frequency bands (simple lo/hi) you could use the LM3915 to drive a bar graph LED display (use two - one for lo, one for hi).
If you want the full audio spectrum then look for a dedicated device - they do exist.
That makes absolutely ZERO sense. It's a good example of what I call "voodoo electronics," in which a person who has no understanding of electronics believes stuff happens by magic.
I have many blinking and colors-changing LEDs all over my home and my yard. I have a sound level indicator in my family room but it is not a spectrum analyser. My experience and understanding of electronics make the magic for it to happen.