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# Window Choice in FIR filter design

Posted on 2004-11-24
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I want to design using the windowed fourier series approach a linear phase FIR lowpass filter of lowest order with the following specifications: passband edge at 0.3pi, stopband edge at 0.5pi, and minumum stopband attenuation of 40dB. Which window function is the best appropriate for this design and why?? (examples: hamming, hanning, blackman....etc)
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Question by:mte01

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Expert Comment

IIRC each window has its advantages and disadvantages.  Some are going to give you better amplitude accuracy, some better phase accuracy.   Some give weird but small artifacts in the stop band, others give regular but larger quirks.

I'd download one of the many excellent filter design applets and play with the window selection buttons.

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Author Comment

I want the window that would provide the filter with the least order
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Expert Comment

Sin^2 t
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Expert Comment

Hmm, I'm mighty fuzzy on this stuff, but I think applying the window just surpresses the endpoint artifacts and how they appear on the amplitude and phase analysis results.   The actual filter design is independednt of this-- the windowingg just helps clear up the picture.

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Yes maybe.....
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Author Comment

The correct window turned out to be the hanning window.........I want to ask the moderator: should I delete this question grg99's answer with a grade of C??
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Accepted Solution

Hi mte01,
I'm an engineering student and i've just studied this functions last semester. Well, after reading your specification, you shall use Hanning Window, Hamming and BlackMan windows functions but Hanning is prefered. This is because with hanning, the Stop Band Attenuation that can be achieve is 44dB ( according to my lecture notes and it's standard). Below is the StopBand Attenuation that can be achieve using the three window functions mentioned:

Hanning 44dB
Hamming 55dB
BlackMan 75dB.

We should take the smaller value of SBA because it's more than sufficient according to your specification.
Cheers :)
SokhodoM
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Author Comment

It's amazing how I thought of deleting the question at the same time that you got the correct answer!!!

Yes, you are correct and thanks for the explanation....
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Expert Comment

You are welcome m8, and thanks for the grade.
Cheers :)
SokhodoM
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Author Comment

if you can sokhodom, also have a look at this question: http://www.experts-exchange.com/Programming/Q_21219067.html
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