I am designing an IIR notch filter using pole-zero placement method. I am trying to convolve the two zero locations using

b1 = [1 exp(i*pi*filterFreq)];
b2 = [1 exp(-i*pi*filterFreq)];
b3 = conv(b1, b2) 

which is producing the output of

b3 =

    1.0000    1.5917    1.0000

when instead I need it to be

b =

    1.0000   -1.5917    1.0000

I feel like this is just a misunderstanding of the math rather than MATLAB. Any advice appreciated.



A zero at $z = e^{j\theta_1}$ corresponds to the transfer function $H_1(z) = 1 - e^{j\theta_1}z^{-1}$. You have an implicit plus sign (rather than minus) in your vectors b1 and b2.

| improve this answer | |
  • $\begingroup$ what an oversight by myself. Thank you! :) $\endgroup$ – Mikey Aug 8 '19 at 0:45

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