What is the process of changing from one key to another within a piece of music called?

The process of changing from one key to another within a piece of music is called modulation. Modulation is a fundamental concept in music composition and performance, as it allows for a shift in tonal center and adds variety and emotional depth to a piece. By modulating, composers can create tension, resolve into a different mood, or highlight specific musical themes.

In contrast, the other terms refer to different musical concepts. Acapella refers to singing without instrumental accompaniment, while articulation pertains to the clarity and distinctiveness of musical notes, influencing how they are played or sung. Intonation refers to the accuracy of pitch in performance, which is crucial for harmonious singing but is separate from the concept of changing keys. Understanding modulation enriches one's musical expression and enhances the ability to interpret varied genres.