What does vibrato refer to in musical performance?

Vibrato is defined as a slight wavering in pitch that is primarily used by singers and string players to enhance the expressiveness of their performance. This technique involves slight oscillations above and below the main pitch, creating a richer and warmer sound. It adds emotional depth and fullness to sustained notes, allowing performers to convey nuances in their music. Singers often use vibrato as part of their vocal technique, while string players utilize it by oscillating the pitch of the note produced by the bowing action. This expressive tool is valuable in many musical genres, contributing significantly to the overall interpretation and stylistic delivery of a piece.

The other options reference different musical concepts: dynamic changes in tempo relate to rubato or accelerando, an increase in volume pertains to dynamic markings, and harmonics involve specific techniques for isolating frequencies on instruments rather than pitch modulation.