Bessel Filter -3dB frequency

The documentation for besself states: "[b,a] = besself(n,Wo) returns the transfer function coefficients of an nth-order lowpass analog Bessel filter, where Wo is the angular frequency up to which the filter's group delay is approximately constant."

Is there a way to determine what frequency one should input in order to obtain a -3dB amplitude response at a specific frequency?

I realize the bessel filter is used primarily for its phase response and group delay, but I would like to plot the response of several poles of filters all normalized to -3dB at 1 rad/sec for comparison purposes as is often done with the butterworth filter.

Thanks for any help you can provide

Answer 1

[filippo tosi]

Dear Craig,

you can achieve this result by applying some scaling coefficients when designing your filter, as shown here:

http://www.crbond.com/papers/bsf2.pdf

For example, in the case of a 3rd order filter with fcut=1000Hz -3dB:

[b,a]=besself(3,1000*2*pi*sqrt(1.755672389));

I hope this helps,

Fil