Although with the advent of the fast Fourier transform and digital filtering the constraints of available analog filter specifications are no longer really pertinent, the tendency to use the ANSI standard frequency bands for reference and comparison is widespread, particularly the so‐called13‐octavebands. However, in problems involving complex spectra with shifting narrow‐band components, it becomes obvious that the13‐octaveapproach is not adequate and may give misleading results, particularly at low frequencies, where the bandwidth is narrow. Similarly, because of their conceptual nature and also the way in which the bands are specified, consistent subdivision into narrow proportional bands is not possible, and such subdivision is now desirable, if not essential. For this reason, a return to the decimal system, in name as well as in fact, is strongly recommended. The problems encountered with standard “13‐octave” bands are discussed in detail, in the context of the band specifications, and alternative methods of band specification, which avoid the problems entirely, are described, including a new look at the concept of “spectrum level.” [Work supported by NUSC.]