# FIR notch filters using the Windowing method

Started by April 13, 2005
```"Jerry Avins" <jya@ieee.org> wrote in message
news:Bb6dnSQA2uHZS_zfRVn-pw@rcn.net...
> Rick Lyons wrote:
>
>    ...
>
> >   I just went through an analysis of narrowband notch FIR
> > filters and discovered that we can build a
> > computationally-efficient 3-tap narrowband FIR notch filter.
> >
> > The FIR filter's coefficients are [1, b, 1].
> > The value for "b" is equal to:
> >
> >    b = -2cos(4*pi*Fnotch/Fs)
> >
> > where Fnotch is the center freq of the filter's notch
> > in Hz, and Fs is the sample rate in Hz.
>
> WOW! Zowie! This I have to plot!

It makes a nice deep notch, but I wouldn't exactly call it narrow-band,
especially with low notch frequencies and considering the bandwidth in terms of
octaves.

```
```Jon Harris wrote:
> "Jerry Avins" <jya@ieee.org> wrote in message
> news:Bb6dnSQA2uHZS_zfRVn-pw@rcn.net...
>
>>Rick Lyons wrote:
>>
>>   ...
>>
>>
>>>  I just went through an analysis of narrowband notch FIR
>>>filters and discovered that we can build a
>>>computationally-efficient 3-tap narrowband FIR notch filter.
>>>
>>>The FIR filter's coefficients are [1, b, 1].
>>>The value for "b" is equal to:
>>>
>>>   b = -2cos(4*pi*Fnotch/Fs)
>>>
>>>where Fnotch is the center freq of the filter's notch
>>>in Hz, and Fs is the sample rate in Hz.
>>
>>WOW! Zowie! This I have to plot!
>
>
> It makes a nice deep notch, but I wouldn't exactly call it narrow-band,
> especially with low notch frequencies and considering the bandwidth in terms of
> octaves.

Yeah. As the French say, tant pis. You generally get what you pay for.

Jerry
--
Engineering is the art of making what you want from things you can get.
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