Audacity is popular, free, open-source, cross-platform audio editor. This talk will introduce Audacity and explain from a Computer Science perspective how a simple, free editor can perform many operations orders of magnitude faster than expensive "professional" editors. While most users see only the graphical interface, Audacity has an embedded scripting language based on the powerful, Lisp-based, Nyquist programming language. I will describe how Audacity interacts with Nyquist and show how to extend Audacity with new signal processing operations. Some examples of how users have extended Audacity include: support for developing podcasts, software to separate multiple songs from LP records into separate files, and new digital audio effects.