Students in introductory physics courses encounter harmonics when they study standing waves on strings and in pipes. The Fourier spectrum, which plots amplitude against harmonic number, can describe all periodic tones imaginable. However, most sounds are aperiodic and therefore have additional spectral components. A real-world application that includes frequencies outside the harmonic series can be found in guitar pedal effects used by rock musicians. This interdisciplinary paper gives the teacher an opportunity to connect frequency spectra to a real-world invention used in the world of rock music. Here the musician wants to extend the natural sound of the guitar by including strange effects to enhance the rock music experience. Students are sure to find this audio application of physics interesting.