My unit on sound and waves is embedded within a long-term project in which my high school students construct a musical instrument out of common materials. The unit culminates with a performance assessment: students play the first four measures of "Somewhere Over the Rainbow"--chosen because of the octave interval of the first two notes--in the key of C, and write a short paper describing the theory underlying their instrument. My students have done this project for the past three years, and it continues to evolve. This year I added new instructional materials that I developed using a freeware program called Audacity. This software is very intuitive, and my students used it to develop their musical instruments. In this paper I will describe some of the inexpensive instructional materials in my sound unit, and how they fit with my learning goals.