Patent ID: 7321913

Claim:
A method of determining filter coefficients for filter stages in a multirate digital filter device to achieve a desired filter response, the method comprising the steps of: (a) determining a plurality of log-scale sample points representing the desired response function on a logarithmic frequency scale, (b) determining a first series of evenly spaced sample points representing the desired response function on a logarithmic time scale, such that the sample points of the first series have an increasing spacing when viewed in a linear time scale, including deriving the sample points of the first series from the log-scale sample points, and (c) determining a respective plurality of filter coefficients for each filter stage from an associated group of sample points out of the first series of sample points, such that each plurality of filter coefficients is determined from determined log-scale sample points, wherein each successive filter stage in the multirate digital filter device is for linearly spaced samples at a sampling rate that is decimated by an integer factor from the previous filter stage, and wherein at least two associated groups of sample points for at least two respective pluralities of filter coefficients for at least two respective successive filter stages have one or more sample points in common.