What is an example of a crescendo?

A crescendo is defined as a gradual increase in volume, which means that music or sound becomes progressively louder over time. This dynamic technique is commonly used in various musical compositions to build intensity and emotional impact. For instance, a crescendo can create excitement or anticipation as the music swells to a climax.

The other options clearly do not describe a crescendo. A sudden decrease in volume would be termed a decrescendo or diminuendo, indicating a drop in loudness rather than an increase. A constant level of loudness does not involve any change in dynamics at all, and a shift from one key to another pertains to harmonic changes within music, unrelated to volume changes. Thus, the correct answer effectively captures the essence of what a crescendo represents in musical terminology.