Patent ID: 7400676

Claim:
A tone quality adjustment device designing method using a type of digital filter which multiplies several fold signals of respective taps of tapped delay lines made up of a plurality of delayers by filter coefficient groups and adds up results of multiplication and outputs a sum, comprising: inputting a numeric value string or function expressing a desired frequency characteristic, carrying out a reverse Fourier transform on said input numeric value string or function, extracting real number terms of a result of the reverse Fourier transform, rearranging a first half portion and second half portion of a numeric value string made up of said extracted real number terms, performing rounding processing of multiplying the numeric value string consisting of said real number terms by 2 n (n: natural number), rounding off all digits right a decimal point and multiplying a result of the rounding processing by ½ n (n: natural number), to generating an output numeric value string as a filter coefficient group of a first filter; and carrying out a predetermined calculation on said numeric value string or function input, applying said reverse Fourier transform, said rearrangement processing and said rounding processing on a result of the predetermined calculation so as to obtain a filter coefficient group of a second filter having a frequency characteristic symmetric to said first filter with respect to a gain reference value as an axis.