Formulae describing frequency selectivity as a function of frequency and level, and their use in calculating excitation patterns.

The auditory filter may be considered as a weighting function representing frequency selectivity at a particular centre frequency. Its shape can be derived using the power-spectrum model of masking which assumes: (1) in detecting a signal in a masker the observer uses the single auditory filter giving the highest signal-to-masker ratio; (2) threshold corresponds to a fixed signal-to-masker ratio at the output of that filter. Factors influencing the choice of a masker to measure the auditory filter shape are discussed. Narrow-band maskers are unsuitable for this purpose, since they violate the assumptions of the power-spectrum model. A method using a notched-noise masker is recommended, and typical results using that method are presented. The variation of the auditory filter shape with centre frequency and with level, and the relationship of the auditory filter shape and the excitation pattern are described. A method of calculating the excitation pattern of any sound as a function of level is presented, and examples and applications are given. The appendix gives a Fortran program for calculating excitation patterns.