The Spectrum Analyzer is a visual device which reads audio information and displays it in 7 frequency bands, from 63Hz to 16kHz, represented by classic LED Bar Graphs. It reads information from any source that can be plugged into it—a computer, a guitar, a synth, a cellphone—or it can read the sound around it through a built-in microphone.
It's pretty freaking rad.
Like all Dr. Scientist pedals, the Spectrum Analyzer can be used with guitar, bass, synths, and many other instruments.