ASA S1.11-2004 (R2009) Historical

This standard provides performance requirements for fractional-octave-band bandpass filters, including, in particular, octave-band and one-third-octave-band filters. Basic requirements are given by equations with selected empirical constants to establish limits on the required performance. The requirements are applicable to passive or active analog filters that operate on continuous-time signals, to analog and digital filters that operate on discrete-time signals and to fractional- octave-band analyses synthesized from narrow-band spectral components. Filter designs are described by an Order number which is usually related to the number of poles in the analog prototype low-pass filter or the number of pole pairs in the analog prototype bandpass filter. The overall accuracy of a filter set is described by a Type number, which is determined by the accuracy of a measurement of a white noise signal, and a required Sub-Type letter, which is determined by the accuracy of the measurement of signals with moderate spectral slopes. Four accuracy grades are allowed: the most accurate for precise analog and digital filters; the next for filters achievable with the technology of the 1980s. The two least accurate grades describe filters which meet the requirements of S1.11-1966. An Appendix is included for reference to terminology used in digital signal processing.