Root and delay parameters for normalized Bessel and Butterworth low-pass transfer functions
Roger M. Golden, James F. Kaiser · IEEE Transactions on Audio and Electroacoustics · 1971
Tables are given for the roots of the normalized low-pass Bessel and Butterworth transfer functions in both Cartesian and polar form. The latter form is especially useful when designing transitional (Butterworth-Thomson) functions. The tables cover the orders 1 through 30 inclusive. In addition, the group delay characteristics for each of the above orders are tabulated for both the Bessel and Butterworth functions.