The modified ultraspherical low-pass filter
J. Attikiouzel, Dang Tan Phuc · International Journal of Electronics · 1978
The problem of approximating the ideal low-pass filter characteristic using modified ultraspherical polynomials is considered. The modification of the ultraspherieal polynomials is achieved by normalizing these polynomials in such a way that their largest absolute extremum is always equal to unity in the interval [-1,1]. A number of amplitude responses can be obtained from this approximation by the specification of two parameters. The filters obtained are compared with other well-known approximations in the frequency and time domain.