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Re: freqz plot question

From: bharat pathak
Subject: Re: freqz plot question
Date: Sat, 12 Sep 2009 03:53:22 +0530

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,

Bharat Pathak

Arithos Designs

DSP Design Consultancy and Technical Trainings.

From: "Scott Raevsky" <address@hidden>
Sent: Friday, September 11, 2009 10:45 PM
To: <address@hidden>
Subject: freqz plot question


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.


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