The basic rate of repetition of a complex periodic waveform, measured in Hz. A complex waveform may be viewed as the result of the addition of a number of sinusoidal waveforms of differing frequencies and amplitudes. The waveform’s fundamental frequency is the highest common factor of the frequencies of the component waveforms.

Some examples:

• Components at 100, 200 and 300 Hz – fundamental frequency = 100 Hz
• Components at 200, 400 and 600 Hz – fundamental frequency = 200 Hz
• Components at 150, 200 and 300 Hz – fundamental frequency = 50 Hz
• Components at 100, 300 and 400 Hz – fundamental frequency = 100 Hz

Note that it is not the case that the fundamental frequency is the same as the lowest frequency component present, as the third example demonstrates. This situation is sometimes called a missing fundamental. Neither is it the case that the fundamental is the same as the spacing between two adjacent components. This is demonstrated by the last example above.

Fundamental frequency is related to the perception of pitch.