[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
## freqz gives weird response

**From**: |
Jurgen Defurne |

**Subject**: |
freqz gives weird response |

**Date**: |
Thu, 29 Sep 2011 09:43:02 +0200 |

Dear all,
I am busy learning poles and zeros, and I have the following function:
1((1 - lz^-1)(1 - l*z^-1))
where l and l* are a conjugate pole pair.
If I create two column vectors B and A:
B A
0 0.5+0.5i
0.5-0.5i
and use zplane(B,A) I get what I expect.
However, when I use freqz, instead of a low-pass filter
response I get a resonator response with one sharp peak.
I do not (really) think that freqz is incorrect, but more
that it is not really clear how to go about using zfreq.
I added some small sample code.
B = [ 0 ];
A = [ 0.5 - 0.5i;0.5 + 0.5i];
figure;
zplane(B,A);
figure;
freqz(B,A);
Recreating this pole/zero plot with a small program call IIR
Explorer, I get a low-pass function.
Regards,
Jurgen

**freqz gives weird response**,
*Jurgen Defurne* **<=**