Digital equalizer capable of varying the center frequency, quality factor, and gain to perform various frequency characteristics

摘要

A digital filter having a band-pass filter characteristic or a band- elimination characteristic is constructed by a designing procedure comprising a step in which a function H(z) is obtained from a Z-transform of a bi-quad transfer function H(s) in a Laplace transfer form comprising conjugate pairs of poles and zeros, and establishing a center frequency of the filter characteristic from the radius of a circle in the s-plane in which the poles and zeros of the bi-quad transfer function H(s) are on the same circle, a step in which a quality factor Q of the filter characteristic is established so as to satisfy the following two equations (I) and (II) in which &sgr;.sub.1 is the real-axis projection part and &ohgr;.sub.1 is the imaginary-axis projection part of the above two poles in the s-plane, and &sgr;.sub.2 is the real-axis projection part and &ohgr;.sub.2 is the imaginary-axis projection part of the above two zeros, and a step in which a gain at the center frequency of the filter characteristic is established from a ratio &sgr;.sub.2 /&sgr;. sub. 1 of the real-axis projection part &sgr;.sub.1 of the poles and the real- axis projection part &sgr;.sub.2 of the zeros in the s-plane ##EQU1##