Audio and MIDI data are fundamentally different, yet intertwined in the world of computer-based music composition and production. While a musical performance may be represented in both forms, MIDI data can always be edited and modified without compromising sound quality, and musical notation can be produced from it rather straightforwardly. Thus, having a performance stored as MIDI data can sometimes be preferable to having it stored as audio data. However, in the absence of a MIDI-enabled instrument, the MIDI data would need to be generated from the audio data, putting some rather severe restrictions on the possibilities. This thesis presents the foundation of an audio-to-MIDI application developed in Java, following an introductory discussion on pitch detection, MIDI, and the general problem of audio-to-MIDI translation. The audio-to- MIDI performance of the application is generally good for music with fairly simple sounds, but more work is needed for it to properly handle the more complex sounds expected in the typical usage scenario.