filter nominal midband frequency

7.08  filter nominal midband frequency. For a set of contiguous one-third octave bandpass filters, frequency of a specified series such as the preferred-frequency series that includes 100, 125, 160, 200, 250, 315, 400, 500, 630, 800, and 1000 hertz, extended by successive multiplication or division by 10. For a set of contiguous octave bandpass filters, the nominal midband frequency is one of a series such as the preferred frequency series that includes 16, 31.5, 63, 125, 250, 500, 1000, 2000, 4000, and 8000 hertz, extended by successive multiplication or division by 10³. Unit, hertz (Hz).

Annotation 1          Preferred frequencies are defined in ANSI/ASA S1.6-1984 (R 2011) American National Standard Preferred Frequencies, Frequency Levels, and Band Numbers for Acoustical Measurements. The reference frequency for Band Numbers is 1 Hz.

Annotation 2          Over any 1:10 range of frequency the average difference between exact and nominal midband frequencies for the G₁₀ frequency ratio is –0.047%; the maximum difference is –0.944%. Over the usual audio range of frequency from 20 Hz to 20,000 Hz the average difference between exact and nominal midband frequencies for the G₂ frequency ratio is –0.202%; the maximum difference is 0.825%.