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Is Bessel filter linear phase?

Question asked by J3627 on Feb 12, 2013
Latest reply on Feb 12, 2013 by BrettG

In the General 2nd Order block, you can select a Bessel LPF.  Is this digital Bessel filter generated using bilinear transform or some other transform?  As I understand, the bilinear transform does not produce a true linear-phase filter:

 

Note that the digital Bessel filter is designed using BLT. That introduces a phase response error due to the frequency warping. In the other words, the linear phase will be considerably distorted if Fc is higher then Fs/4 approximately. You should use impulse invariant approach or other phase preserving technique to design Bessel filter for high frequencies.

 

http://freeverb3.sourceforge.net/iir_filter.shtml

 

The only advantage of a Bessel design over a Butterworth or Chebyshev is that the phase response is nearly linear throughout the passband, i.e. the group delay is almost constant throughout the passband.  The ``warping'' inherent in the bilinear transform method upsets this linearity.

 

http://www-users.cs.york.ac.uk/~fisher/mkfilter/mzt.html

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