In a car, does matching the EQ of both the left and right side using IIRfilters mean that I'm matching the phase of each side? I have someone telling me that the car's environment is mostly minimum phase and that matching the left and right side will match its phase response. I have never heard of such a thing. I know they would match amplitude but would highly doubt they're matching the phase which is something an FIR filter would actually do. Any help would be appreciated.

  • $\begingroup$ you should ask them for mathematical clarification of what they mean by minimum phase ? $\endgroup$
    – Fat32
    Aug 21, 2019 at 12:55
  • $\begingroup$ They are definitely not going to know that... I do know that in a car's environment there are non-minimum phase regions. I used Room EQ Wizard to identify these regions by viewing the Excess Group Delay graphs. So it got me thinking, when using FIR filters, those regions where there is non-minimum phase, the phase information is retained between both L and R speakers; which should result in better imaging compared to using solely IIR filters. $\endgroup$
    – Tony N.
    Aug 22, 2019 at 13:44

1 Answer 1


Two minimum phase IIR filters with different magnitude responses generally will have different phase responses. But two minimum phase IIR filters with exactly same magnitude responses will exactly have same phase responses. (How can two systems with exactly same transfer functions have different magnitude/phase responses?). If the first filter is a minimum phase filter and the second filter has exactly same magnitude response but different phase response then the second filter is not minimum phase.

In contrary, two linear phase FIR filters with different magnitude responses may have exactly same phase responses when the required conditions are fulfilled. (E.g same delays, same symmetric types, and no negation).

  • $\begingroup$ This was exactly what I was looking for. I now need to look up what symmetric types and negation is. If you have time and wish to further explain that'll be great! =) $\endgroup$
    – Tony N.
    Aug 22, 2019 at 13:03
  • $\begingroup$ @TonyN. Type I to IV symmetry. Negation: I mean for 180 degree phase shift, e.g a = [1,2,1] b = [-1,-2,-1]. $\endgroup$
    – mfcc64
    Aug 22, 2019 at 14:31

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