Automatic arrangement is the problem of transforming an input score into a full orchestration, e.g. realized with samples. A subproblem, on which arrangement depends, is to establish the dynamic levels of individual parts, their articulations, and how parts are to align. A new kind of structural analysis is described: the interpretation of music means the delineation of existing structure, so that the performance synchronizes with the music. These ideas are realized in a system that creates fully articulated string orchestra renditions of concerti by Bach and Vivaldi. While still at an early stage, the system demonstrates how structural analysis can be deployed to solve complex musical tasks. We conclude with some speculations about the future of musical practices as suggested by this research.