This standard defines the preferred frequencies, or nominal band-center frequencies to be used for acoustical measurements. Frequency levels or band numbers are associated with these sets of frequencies and the preferred frequencies are rounded values obtained from those for which the corresponding frequency levels ore band numbers are integers.
ANSI/ASA S1.6-1984 history
1984ANSI/ASA S1.6-1984 Preferred Frequencies, Frequency Levels, and Band Numbers for Acoustical Measurements