- 1: extent of dignity, excellence, or splendor
- 2: the quality or state of being ample : fullness, abundance
- 3: the extent or range of a quality, property, process, or phenomenon: as
- a : the extent of a vibratory movement (as of a pendulum) measured from the mean position to an extreme
- b : the maximum departure of the value of an alternating current or wave from the average value
The amplitude of a periodic variable is a measure of its change over a single period (such as time or spatial period). There are various definitions of amplitude which are all functions of the magnitude of the difference between the variable's extreme values.
In general, the use of peak amplitude is simple and unambiguous only for symmetric periodic waves, like a sine wave, a square wave, or a triangular wave. For an asymmetric wave (periodic pulses in one direction, for example), the peak amplitude becomes ambiguous. This is because the value is different depending on whether the maximum positive signal is measured relative to the mean, the maximum negative signal is measured relative to the mean, or the maximum positive signal is measured relative to the maximum negative signal (the peak-to-peak amplitude) and then divided by two. In electrical engineering, the usual solution to this ambiguity is to measure the amplitude from a defined reference potential (such as ground or 0 V). Strictly speaking, this is no longer amplitude since there is the possibility that a constant (DC component) is included in the measurement.
Pulse amplitude is measured with respect to a specified reference and therefore should be modified by qualifiers, such as "average", "instantaneous", "peak", or "root-mean-square".