The base frequency, the lowest sine wave frequency in a range of frequencies. The fundamental is the original frequency from which harmonics are developed. Harmonics are additional frequencies that are multiples of the fundamental. For example, a fundamental of 2 kHz would have harmonics of 4 kHz, 6 kHz, 8 kHz and so on up beyond audibility with each harmonic decreasing in amplitude or power. The fundamental is the base frequency from which the others are developed.