filter exact midband frequency

7.07  filter exact midband frequency. Geometric mean of the lower and upper band-edge frequencies, symbols f₁ and f₂, respectively, of a bandpass filter. Midband frequency, symbol f_m, has a specified relationship to a reference frequency, f_r, such that the ratio of the exact midband frequencies of any two contiguous bandpass filters of a specified fractional octave bandwidth is the same. When the denominator of the bandwidth designator, 1/b, is an odd number (e.g., 1/3 octave), exact midband frequencies of any filter in a set of filters are determined from