In scientific terminology, amplitude is the level of strength of sound vibrations — more precisely, the amount of energy they contain and convey. As big guitar amplifiers attest, very small string vibrations can be amplified until the energy in the air transmitting them rattles the eardrums.

In musical terminology, the level of sound is called its dynamics. Musicians use subtle dynamic gradations from very soft to very loud, but they have never worked out a calibrated scale of dynamics, as they have for pitch. The terms used are only approximate. Like the indications for tempo, the terms used for dynamics are in Italian.

The main categories are simply loud and soft, forte (pronounced fór-teh) and piano, which may be qualified by expanding to “very loud” or “very soft” and by adding the Italian word for “medium,” mezzo (mét-so):

Changes in dynamics can be sudden (subito), or they can be gradual — a soft passage swells into a loud one (crescendo, “growing”), or a powerful blare fades into quietness (decrescendo or diminuendo, “diminishing”).