sound spectrum
the representation of sound in terms of its frequency composition. Any physically realizable sound and, more generally, any waveform can be represented as a function of time or of frequency. These representations are uniquely related by the Fourier transform or Fourier series (see Fourier analysis). The spectrum is the frequency-domain representation and consists of the amplitude spectrum (or power spectrum) and the phase spectrum. Both are necessary to describe the sound completely. For example, a sound played backward has the same amplitude spectrum but an altered phase spectrum, and usually the sounds are perceptually very different. Periodic sounds have a line spectrum with a nonzero amplitude only at discrete frequencies. Other sounds have a continuous spectrum; the spectrum is then described in terms of spectral density, which involves units of amplitude or power per hertz. Sound spectra are useful
partly because the mammalian auditory system performs an imperfect Fourier analysis. Also called acoustic spectrum; tonal spectrum. See tonotopic organization.