A waveform specifies how a wave-related quantity varies with time or position. For an electrical recording it may be , an electric potential difference; for sound it may be the sound pressure . Both the shape and its physical scale matter: a normalized trace alone omits amplitude and time units.
For example,contains a fundamental frequency and a third harmonic. It has the same period as the first sinusoid but a different shape. Varying the relative phase of the third harmonic changes that shape even when the two component amplitudes stay fixed. A Fourier series describes periodic waveforms through such harmonic amplitudes and phases.
A microphone and oscilloscope can record an acoustic waveform after calibration. The recording is also affected by the instrument's frequency response and signal sampling: a narrow-band microphone smooths sharp features, and inadequate sampling can misrepresent oscillations. The observed waveform therefore represents the signal together with the measurement chain.
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