Octave and fractional octave band digital filtering based on the proposed ANSI standard

A software implementation has been developed which is based on the proposed ANSI standard "Specification for Octave-Band and Fractional Octave-Band Analog and Digital Filters". This standard is a revision of S1.11- 1966 (1976) "Octave, Half-Octave, and Third-Octave Band Filter Sets". Significant changes to the standard are the inclusion of digital filters, definition of octaves based on powers of 2 in addition to powers of 10^0.3, and relaxation of filter symmetry requirements. The implementation is divided into three parts: 1) fractional octave-band filter design, 2) an efficient decimation-in-time algorithm to perform the filtering, and 3) application of A, B, C, and D weighting curves. Numerical calculations and graphical displays of the output of the filters for white noise input verify the efficacy of the implementation. An evaluation of the digital filter design compared to the proposed standard elucidates the difficulties in maintaining similar specifications in the analog and digital domains.