How the presence of an audience shapes skilled performance has been studied for over a century, largely through laboratory tasks testing whether being watched improves or impairs. Music offers a richer test case: a demanding skill performed for others in which how the performance changes can be measured, not only whether it improved. We compared an expert pianist’s performance of the same six-piece programme alone in a private rehearsal and a public concert, measuring her motion, beat-level timing, sound intensity, and pedalling. The two performances were remarkably similar, with the pianist reproducing her expressive interpretation with high fidelity across every feature. Further, the passages she had marked as most expressive in the score were no more affected by the audience than the rest. Despite this overall consistency, audience presence introduced small but reliable changes: greater variability in her motion, timing, and soft pedal use, and at the least intense moments in the music (as rated by listeners) she drew out the tempo and shaped the quietest passages more with the soft pedal in concert. For this performer, an audience did not impair her performance but facilitated it, supporting a faithful execution of her prepared interpretation while increasing expression through enhanced variability.
