Forums

Notch filter

Started by OZ 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 fit in your time/memory constraints. 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-] >