I heard that an IIR filter has delay and phase shift effect, but not clearly what are they. For example, 1-pole Lowpass has 90 degree phase shift, 2-pole Lowpass has 180 degree? So does it mean two 2-pole Lowpass filters has 360 degree phase shift? Beside the HighPass, LowPass, AllPass filter, other IIR filter like LowShelf, HighShelf, Peak... has phase shift too?
When I apply an IIR filter using biquad transfer function, does it has any phase shift diffirent if I use direct form I (4 delay registers) vs direct form II (2 delay registers)?
If IIR filter has phase shift, the phase shift occurred at the filter's target frequency, or all the frequencies? How can I phase shift (all frequencies) 90 degree clockwise & counterclockwise just using AllPass filter?

I know some of my questions are noob, but I'm just study dsp myself, and there're somethings that I really confused about. Sorry for my bad English too :)

  • $\begingroup$ As Rick says, your question is very unclear. All realizable, non-trivial filters have a phase shift. The phase shift generally depends on the frequency, and changes with frequency. Higher-order filters can induce a higher phase shift than lower order filters. Check out the different sorts of IIR filters: Chebyshev, Bessel, etc. and look at their phase responses. $\endgroup$
    – Peter K.
    Jul 3 '15 at 14:59

I believe you have received no answers to your questions because your first three questions are so strange, so puzzling, that no one where to start to even begin to compose answers. See:




Good Luck.

  • $\begingroup$ About the phase shift and frequency, it's seem that the phase response is shifted from 0 zo Z degree (correspond to frequency 0 Hz to x Hz). But I still don't know how the phase response is effected by diffirent IIR filter coefficients. Are there any way to track the phase shift and biquad coefficiets? $\endgroup$
    – MPhuc
    Jun 24 '15 at 13:02
  • $\begingroup$ Hi. I don't know what phase shift you are looking at, so your 1st sentence has no meaning for me. You can see how an IIR filter's coefficients affect the filter's phase by writing the z-domain transfer of you filter. (It will be a ratio of polynomials in terms of variable 'z'.) Then replace each 'z' with e^(jw), where 'w' is the frequency variable measured in radians. The Oppenheim & Schafer and Proakis & Manolakis textbooks have methodical and thorough descriptions of all of this. (What you're asking is: "How do IIR filters work?" And that question can't be answered in any detail here.) $\endgroup$ Jun 26 '15 at 16:32
  • $\begingroup$ Actually I want to know how the phase response, frequency response... is effected by applying multi IIR filters. I'm a programmer, so I just know how to code, but don't understand how it work. I think I'll have to study more about the theory before going else. Thanks for your suggestion, I'll try to have a look at it. $\endgroup$
    – MPhuc
    Jun 27 '15 at 11:55
  • $\begingroup$ Hi. If you have moderate skill with algebra and a decent understanding of complex numbers, then with enthusiasm on your part you should be able to learn what you need to know. Good luck. $\endgroup$ Jun 28 '15 at 19:08

Not the answer you're looking for? Browse other questions tagged or ask your own question.