Since the th spectral sample is properly regarded as a measure of spectral amplitude over a range of frequencies, nominally to , this range is sometimes called a frequency bin (as in a ``storage bin'' for spectral energy). The frequency index is called the bin number, and can be regarded as the total energy in the th bin (see §7.4.9). Similar remarks apply to samples of any bandlimited function; however, the term ``bin'' is only used in the frequency domain, even though it could be assigned exactly the same meaning mathematically in the time domain.