From driving to expressive music performance: ensuring tempo smoothness

This paper focuses on the mapping strategies in the interface design for the Expression Synthesis Project (ESP). The goal of ESP is to use the metaphor of driving to allow non-experts to interactively create expressive renderings of music pieces. In ESP, the road represents the music, with bends and straight segments representing places where one might slow down and speed up respectively. The user controls the tempo (rate of beats) and dynamics (amplitude) by the way s/he drives through the road. Our design objective in the ESP environment is to define mapping strategies that guarantee tempo smoothness, a hallmark of expert and practiced performances, under all driving conditions. Because the road has non-zero width, several strategies exist for mapping the car's position on the road to the musical score. We propose mapping strategies that ensure tempo smoothness, and provide mathematical and empirical proofs for the success of these strategies.