Amplitude

The maximum deviation from the average or equilibrium value of any repeatedly changing quantity, such as the position of a vibrating object, pressure, velocity, voltage, current and many others. The amplitude of a sound wave is the maximum amount by which the instantaneous sound pressure differs from the ambient pressure. See diagram under simple harmonic motion.

Two cycles of a sine wave showing the amplitude of the pressure variation.

The variation of (maximum) amplitude over time is called the envelope of the sound.

Compare: Intensity, Loudness, Power, Volume. See also: Decay Time, Oscillation, Particle Velocity, Rise Time, Root Mean Square, Sine Wave, Threshold of Hearing, Tremolo, Waveform.