Final answer:
Changes in volume levels as a note is played represent the intensity or loudness of the sound, which is tied to amplitude variations.
Step-by-step explanation:
The changes in volume levels as a note is being played represent intensity, which is perceived as loudness. Loudness measures the perceived intensity of a sound and has units of phons. When we hear changes in volume, we're experiencing variations in the intensity of the sound waves, which can be associated with amplitude. It is crucial to differentiate loudness from other sound characteristics such as pitch, which relates to frequency, and timbre, which refers to the unique quality or tone of the sound that allows us to distinguish between different instruments playing the same note. Timbre involves a complex interplay of frequencies and intensities which make an instrument sound unique, and is more subjective in nature than pitch or loudness.