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## Re: freqz plot question

 From: Scott Raevsky Subject: Re: freqz plot question Date: Fri, 11 Sep 2009 15:34:51 -0700

```Thanks.  I should clarify that I know these concepts well.  However,
whenever I have seen frequency plots before, they include magnitude
and phase--two separate plots.  The "pass band" and "stop band" (if
they truly exist) are plotted on the magnitude plot.  But freqz in
octave plots two separate plots for "pass band" and "stop band," which
makes no sense to me.  Why does it do this?

On 9/11/09, bharat pathak <address@hidden> wrote:
> Dear Scott,
>
> when we design any digital filter, example low pass, high pass,
> band pass and band stop. the filter is supposed to pass certain
> frequencies to the output and stop certain other frequencies.
>
> practically we cannot stop the frequencies, we just attenuate
> them enough such that they do not fall in the dynamic range
> of the datapath. for example if your datapath is 8 bit (DR = 40 dB)
> then if you provide 40dB attenuation (1/100 in linear) to incoming
> signal of full strength then we would not see such signal at the
> output, provided the output datapath is also having 8 bit precision.
>
> hence stop band is the region in frequency domain magnitude response
> plot where those input signals whose frequency lies in the stop band
> region would undergo certain attenuation before coming out of the
> processing module.
>
> hope this gives some clarity,
>
> Regards
> Bharat Pathak
>
> Arithos Designs
> www.Arithos.com
>
> DSP Design Consultancy and Technical Trainings.
>
> --------------------------------------------------
> Sent: Friday, September 11, 2009 10:45 PM
> Subject: freqz plot question
>
>> Hello,
>>
>> It's been years since I used Matlab, but one thing I remember is freqz
>> plotting the mag and phase response.  In octave, freqz plots a pass
>> band, a stop band, and phase.  What is the stop band for, and why is
>> it seperate from the pass band?  Seems like it should be just mag and
>> phase, where the pass and stop bands are part of the mag plot.
>>
>> Thanks
>>
>> --
>> Sent from my mobile device
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