Notch filter

Started by May 10, 2005
```Hi,
I am searching a mathematical solution for a notch filter.

I measured a signal with a ADC and I want to kill one frequency (50Hz)
out of the measurement data.

Does anyone of you know a mathematical function for a notch filter ?

best regards
Oliver
```
```On Tue, 10 May 2005 12:22:45 GMT, OZ <Oliver.Zind@web.de> wrote:
> Hi,
> I am searching a mathematical solution for a notch filter.
>
> I measured a signal with a ADC and I want to kill one frequency (50Hz)
> out of the measurement data.
>
> Does anyone of you know a mathematical function for a notch filter ?
>

There are infinitely many, though I suppose you can limit yourselves to
analog filters that are practical to construct and digital filters that

Take a look at the Scientist and Engineer's Guild to DSP over here:

http://www.dspguide.com/pdfbook.htm

Read chapters 14-21.  There are examples of exactly what you want to do.

Charles

```
```Be aware that if you have a signal contaminated by AC line noise, that
this line noise often contain harmonics of the 50 Hz (or 60Hz in the
US) as well.

If it sounds like a BUZZ instead of a hum, it has harmonics.

Mark

```
```in article yg2ge.198756\$cg1.137609@bgtnsc04-news.ops.worldnet.att.net,
Charles Krug at cdkrug@worldnet.att.net wrote on 05/10/2005 09:01:

> On Tue, 10 May 2005 12:22:45 GMT, OZ <Oliver.Zind@web.de> wrote:
...
>> I measured a signal with a ADC and I want to kill one frequency (50Hz)
>> out of the measurement data.
>>
>> Does anyone of you know a mathematical function for a notch filter ?
>
> There are infinitely many, though I suppose you can limit yourselves to
> analog filters that are practical to construct and digital filters that
> fit in your time/memory constraints.

if the latter (digital filter), you can check out the biquad notch filter at
the Audio EQ Cookbook at harmony-central.com .

--

r b-j                  rbj@audioimagination.com

"Imagination is more important than knowledge."

```
```Hi,
thanks a lot for the tips. I will check.

Greetings Oliver
```
```"OZ" <Oliver.Zind@web.de> wrote in message
news:4280a789.21786457@news.btx.dtag.de...
> Hi,
> I am searching a mathematical solution for a notch filter.
>
> I measured a signal with a ADC and I want to kill one frequency (50Hz)
> out of the measurement data.
>
> Does anyone of you know a mathematical function for a notch filter ?
>
> best regards
> Oliver
A high-pass filter should do the trick - don't need a notch normally.

Rimmer

```
```On Tue, 10 May 2005 12:22:45 GMT, Oliver.Zind@web.de (OZ) wrote:

>Hi,
>I am searching a mathematical solution for a notch filter.
>
>I measured a signal with a ADC and I want to kill one frequency (50Hz)
>out of the measurement data.
>
>Does anyone of you know a mathematical function for a notch filter ?
>
>best regards
>Oliver

Hi,

here's an efficient 3-tap FIR filter that you might
want to consider.  The filter's 1st and 3rd coefficients
are both ones.  The center coefficient is

-2cos(2*pi*Fn/Fs)

where Fn is the notch location in Hz, and Fs
is the sample rate in Hz.

Good Luck,
[-Rick-]

```
```So easy ? I will try it. Thanks

Oliver

>On Tue, 10 May 2005 12:22:45 GMT, Oliver.Zind@web.de (OZ) wrote:
>
>>Hi,
>>I am searching a mathematical solution for a notch filter.
>>
>>I measured a signal with a ADC and I want to kill one frequency (50Hz)
>>out of the measurement data.
>>
>>Does anyone of you know a mathematical function for a notch filter ?
>>
>>best regards
>>Oliver
>
>Hi,
>
>  here's an efficient 3-tap FIR filter that you might
>want to consider.  The filter's 1st and 3rd coefficients
>are both ones.  The center coefficient is
>
>   -2cos(2*pi*Fn/Fs)
>
>where Fn is the notch location in Hz, and Fs
>is the sample rate in Hz.
>
>Good Luck,
>[-Rick-]
>

```