Before there was digital music and fancy computers and music software, people use to employ the power of the electric color organ (now more commonly known as the "light organ") to add some visuals in sync with their music. MAKE shows you how to build your own sound-to-like circuit— your very own light organ!
Schematics for building such a beast based on AC power and incandescent bulbs can be be found fairly easily on the web, but plans for comparable LED-based designs seem a bit harder to come by, until now…
Collin built his analog LED Color Organ (a larger updated schematic can be found here to enhance his aural experience, and it was adapted from Aaron Cake's 3 Channel Spectrum Analyzer. The circuit uses 4 operational amplifiers plus ultra-bright 5mm LEDs to respond visually for bass, mid, and treble frequencies. A parts bundle for building your own incarnation of the project is now available from Jameco.
In order to simplify the construction process, Collin drew up and printed a label specifying the pinout for quad op amp ICs. Those interested in printing their own can download the design here.