Re: freqz question (clarified)

[Julius Smith]

I agree that freqz should simply plot the magnitude and phase 
response of the filter.  Since the arguments to freqz are merely 
filter coefficients B and A, there is no guarantee that the concepts 
of "pass band" or "stop band" make any sense for the given filter. 
For example, what if B/A is an allpass filter?

We ARE guaranteed, on the other hand, that every filter B/A (with 
A(1)==1) has a frequency response, and the most commonly desired 
frequency-response display, in my experience, is magnitude and phase 
versus frequency.

I would be happy implement this change (magnitude in dB, phase in 
degrees), but freqz appears to be in the base Octave distribution, 
while I can only change things in octave-forge, as far as I know.

- jos

At 02:03 PM 9/12/2009, Scott.Raevsky wrote:
> Content-class: urn:content-classes:message
> Content-Type: multipart/alternative;
>         boundary="----_=_NextPart_001_01CA33E4.15CEB18C"
>
> Hello,
>
> Just to clarify my previous question, Matlab's output of freqz is as follows:
>
> freqz(b,a,...) plots the magnitude and unwrapped phase of the 
> frequency response of the filter. The plot is displayed in the 
> current figure window.
>
> Why does Octave's freqz not plot magnitude and phase?  Instead it 
> plots 1) pass band, 2) stop band, and 3) phase.  Plotting a separate 
> pass band and stop band doesn't make sense to me.
>
> Thanks
>
>
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Julius O. Smith III <address@hidden>
Prof. of Music and Assoc. Prof. (by courtesy) of Electrical Engineering
CCRMA, Stanford University
http://ccrma.stanford.edu/~jos/