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Topic: Why is the number of decimation FIR filter states different with that
of number of numerator?

Replies: 1   Last Post: Apr 10, 2013 2:45 PM

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 Navan Posts: 67 Registered: 7/20/06
Re: Why is the number of decimation FIR filter states different with that
Posted: Apr 10, 2013 2:45 PM

Hi,

Polyphase filters are implemented by decomposing the original filter into several smaller filters that run on decimated signal. The number of filters is equal to the decimation factor. For an FIR filter the number of states is equal to (number of coeffecients - 1). So if there are say 6 filters each having 97 coefficients then you have a total of 582 (97*6) coefficients and 576 (96*6) states.

Navan

fl <rxjwg98@gmail.com> wrote in message <fb687bb3-7c7c-45c7-a40d-4d67722fd26d@googlegroups.com>...
> Hi,
> I design a decimation low pass filter (decimation 16). It is an FIR, low pass 16 Hz, stop frequency is 50 Hz, sampling rate is 10000 Hz. I use filterbuidler design this filter. To my surprise, when I click the mfilt.firdecim variable, it shows:
>
>
> FilterStructure: Direct-Form FIR Polyphase Decimator
> Numerator: [1X582 double array]
> State: [576X1 double array]
> ...
>
>
> How to explain the difference between Numerator and State?
>
> Thanks,

Date Subject Author
4/9/13 fl
4/10/13 Navan