The extent to which a waveform (as displayed on an oscilloscope) rises above, or falls below, the X-axis. The difference between the highest point and the lowest point is referred to as the peak ampltude. Various mathematical schemes such as root-mean-square (RMS) exist which average the amount of time the signal is above or below the axis; these measure, for example, the amount of power required to amplify the signal to a given peak amplitude. The average amplitude is proportional to the volume of the signal.

See also amplitude modulation, envelope.

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