DOI: 10.1145/1095534.1095541This special issue on music visualization focuses on the visual conveyance of music structural information through the automated analysis of digital music and the graphical rendering of its analytical forms. Music can be described as highly organized sounds that exhibit time-varying structures in the pitch (frequency) and time domains. When we listen to music, our minds group pitch structures into horizontal streams (such as melodies) and vertical bunches (such as chords and keys). These pitch collections create musical contexts that situate and orient our hearing of the music. It is the visualization of these time-varying pitch contexts that forms the common theme among the contributions in this special issue.In music-theoretic terms, all four articles are concerned with the tonal structure of music. Tonal structure emerges in music that is tonal, music for which the pattern of notes generates the perception of varying levels of stability amongst the pitches. The term "tonal" applies to almost all of the music that we hear. Computer systems for music visualization that automatically capture and display such structures will enable people to see, and better understand, the tonal patterns that they hear.The large-scale availability of music in digital format, coupled with the rapid increase in computational prowess, has made the automatic visual rendering of musical structure more accessible than ever. According to Jeremy Strick, one of the organizers of the Visual Music exhibit (2005) at the Los Angeles Museum of Contemporary Art and Hirshhorn Museum of the Smithsonian Institute, "In digital media, ... music and visual art truly are united, ... They are created out of the same stuff, bits of electronic information, infinitely interchangeable. ... the aspiration to novel experience created by the compounding of sensation and association has never been more possible" [Strick 2005, p.20]. Even though scientific visualizations of musical structure do not pretend to be fine art, the interlocking of visual and musical sensations featured in this collection similarly seeks to evoke what might be illusive mental associations between music and its analytical structures through visual mediation.