spj@spanky.UUCP (09/01/83)
Frankly, I am puzzled by the statements on the net that all filters have the same attenuation rate ( for the same order ) regardless of the filter type. I have read numerous papers that cite differences in the attenuation rates for Besel and Butterworth filters. The ELECTRONIC FILTER DESIGN HANDBOOK by A. B. Williams reproduces attenuation charts from HANDBOOK OF FILTER SYNTHESIS by A. Zverev for both Bessel and Butterworth low pass filters ( the high pass are symmetrical). According to these charts the following is true: Response at 2Fc Response at 4Fc Response 10Fc Butterworth (4) -24db -48db -80db Bessel (4) -12db -34db -65db These figures are read from the graphs so are approximate. Steve J.