1. Amplitude and phase characteristics as a function of frequency for the components of a wavetrain or wavelet. See Fourier analysis. 2. Filter response characteristics. See transfer function. 3. Quantities displayed in order to show the relative content of various components. Thus a velocity spectrum (or normal-moveout spectrum) shows the amount of coherent energy which appears to have various amounts of normal moveout as a function of arrival time. A dip spectrum shows the amount of coherent energy which appears to have various amounts of dip moveout (or apparent velocity).