An approximation procedure for selective linear phase filters

A method is proposed for the simultaneous approximation of attenuation and group delay characteristics of analog and digital filters. The attenuation is approximated to be equal ripple in the passband and the stopband, while the group delay is equalized in the passband using a least-mean-square norm. The number of attenuation ripples in the passband, and the degrees of freedom for the group delay equalization can be traded off for the best possible approximation.