Amplitude
The size of a sound wave's vibration, measured as its greatest displacement from rest, which determines loudness.
Also called: amplitude of a wave, wave height
Amplitude is the size of a vibration, measured as the greatest displacement from the resting position of the air or the vibrating body. For a sound wave, greater amplitude means greater pressure change and a louder sound. Amplitude does not set pitch. A tone at 440 Hz can be played at any amplitude and still sound as A4. Loudness is perceived on a logarithmic scale. Doubling the pressure amplitude raises the sound level by about 6 decibels, which listeners hear as a clear increase but not a doubling of loudness. In a vibrating string, amplitude is how far the string moves from its rest line. Amplitude also shapes the envelope of a note, which rises at the attack, peaks, and falls on release.
Related terms
- FrequencyThe number of complete vibration cycles per second, measured in hertz (Hz), which sets a sound's pitch.
- TimbreThe quality of a sound that lets listeners tell two sources apart at the same pitch and loudness.
- DynamicsThe relative loudness of music, shown by markings such as p for soft and f for loud, and by hairpins for gradual change.