This paper describes an empirical study of source code visualisation as a means to communicate the programming process in "live coding" computer music performances. Following an exploratory field study of a live-coding performance at an arts festival, two different interaction-driven visualisation techniques were incorporated into a live coding system. We then performed a more controlled laboratory study to evaluate the visualisations' contributions to the audience experience, with emphasis on the (self-reported) experiential dimensions of understanding and enjoyment. Both software visualisation techniques enhanced audience enjoyment, while the effect on audience understanding was more complex. We conclude by suggesting how these visualisation techniques may be used to enhance the audience experience of live coding.