  We present a new system for real-time visualisation of music performance,
focused for the moment on a fugue played by a string quartet. The basic
principle is to offer a visual guide to better understand music using
strategies that should be as engaging, accessible and effective as possible.
The pitch curves related to the separate voices are drawn on a space whose
temporal axis is normalised with respect to metrical positions, and aligned
vertically with respect to their thematic and motivic classification. Aspects
related to tonality are represented as well. We describe the underlying
technologies we have developed and the technical setting. In particular, the
rhythmical and structural representation of the piece relies on real-time
polyphonic audio-to-score alignment using online dynamic time warping. The
visualisation will be presented at a concert of the Danish String Quartet,
performing the last piece of The Art of Fugue by Johann Sebastian Bach.
