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Does increasing sampling size help to keep noise down ?

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watertreader

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Does increasing sampling size help to keep noise down or is there any method to keep noise down by increasing samplng size if the noise is a fixed but unknown constant or gaussian in nature?

Thanks
 

Increase sampling

incrasing sampling rate will definately reduce the noise but required more space. hence sampling rate should be 2.1-3 times of of input frequency.
 

Re: Increase sampling

What about the sampling size? ie the number of samples? My sampling rate is almost 20 times of the interest frequency.

THanks
 

Re: Increase sampling

An analog, low-pass filter prior to the input of the ADC eliminates or significantly reduces aliased noise. The corner frequency of the filter must be lower than fsampling/2. Increasing the order of the filter can minimize the noise.
 

Re: Increase sampling

If the noise is contributed mainly by my acquisition card, would it be possible for me to amplify the signal first before sampling and digitising?
 

Re: Increase sampling

Gaussian noise will not go out if you increase the number of samples or the resolution (8 to 16 or 24 bit) because it is mixed within the signal. Sampling the signal will sample the noise.
Increasing number of samples (oversampling) is used just to make sure you won't get aliasing. Increasing resolution reduces quantization noise, not gaussian noise.
If what you want is to eliminate a constant permanent noise from a signal you should first pass this signal through a differential amplifier with a high CMRR (Common mode rejection ratio) and then perform the sampling.
 

Increase sampling

Hi

definetely there is a gain in sampling at a rate higher than the Nyquist one, and you can not filter it out as it was said before.

In order to prove my point do the following, let us assume that the Nyquist frequency require X samples from you signal, but you increment the sampling rate in a factor A, therefore, you have now AX samples of your signal. Take this AX samples and divide them in sets of A samples, find the average of them and you will end up with X samples for which the higher the value of A, the better the resulting signal resemble your noiseless signal.

good luck
 

Re: Increase sampling

Hi,

I think the noise I would want to reduce would be the noise in the backend, probably quantisation noise from the digital sampler. SO by increasing number of samples(not sampling rate), I could improve the SNR?

Thanks again
 

Increase sampling

After digitizing pass it through a digital low pass filter that will reduce the noise, set the cut of frequency depending on the signal frequency interested.
 

Re: Increase sampling

the area under the noise spectrum is always a constant. so on incresing the sampling rate, the noise spectrum widens in length and to maintain the same area comes down in height. by low pass filtering we take that part of the signal we want. this is called oversampling.
 
Re: Increase sampling

amriths04 said:
the area under the noise spectrum is always a constant. so on incresing the sampling rate, the noise spectrum widens in length and to maintain the same area comes down in height. by low pass filtering we take that part of the signal we want. this is called oversampling.
Click to expand...

so increasing the sampling rate and low passing it will further reduce the noise?

Thanks
 

Re: Increase sampling

yes exactly. you are right. the oversampling technique would make sense only when it is later low-pass filtered.
 

Re: Increase sampling

well what about increasing the sample length? would it work?
 

Re: Increase sampling

you will have to define what you term noise. if there is already a noise corrupted signal, noo matter how well you sample, you cannot change the same. but if it is the quantization effect that you talk off, then by improving the no of levels on the quantizer, you can decrease the noise and improve net SNR. also good care has to be taken during sampling to avoid out of band aliasing.
 

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