Finding the fundamental frequency of a periodic wave, acoustic tone, or electrical signal involves identifying the lowest frequency component that dictates the repetition rate of the entire waveform. In musical acoustics, you can determine it by analyzing the pitch of a vibrating string or air column using digital spectrum analyzers, frequency counter software, or a Strobe tuner. In mathematical and signal processing applications, you analyze the Fourier transform or power spectral density of a signal to locate the primary peak frequency divider from which all higher integer-multiple harmonic frequencies are derived.