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Topic: How to calculate Signal to Noise Ratio (Read 5 times) previous topic - next topic

fkeel


I need to compare the signal to noise level of two sensors.

Is there some standardized way of doing this? Wikipedia & ehow and the rest of the internet seem to magically assume I already know the power of the noise & the power of the signal.

I could use a filter to seperate high-frequency parts of the signal from low frequency parts of the signal and then compare the magnitude of these two values. However, if I did this I can just randomly change the parameters of the filter and come up with either really good or really bad results.

So my question stays: Is there a standardized way of measuring signal to noise ratio of a given sensor/circuit?

thanks
p.

IngHooch

First of all, can you assume that the noise is white?
The brightest flame burns quickest

fkeel

no. I dont know anything about the noise.

in both cases its an analogue sensor connected to a 10 bit AD converter.

I guess I could just measure the noise without changing the input to the sensor. This should give me a pure noise signal. I can then take the root mean square of that... and then what?
Or I calculate the distribution of the noise and then... ?

The other problem is: how do I measure the signal without the noise? I can apply a low-pass filter, but by doing so I manipulate the signal ...

*

lets just assume that the noise *is* white. what then?

*

I am pretty sure I can find a method of calculating signal to noise ratio. I am just trying to figure out if there is a scientifically "correct" way of doing it.

fkeel

can anyone help me with this? some recommended reading or something?

MarkT

The standard way I think to measure a signal in the noise is to compare with a signal of known power - ie you take a strong signal, put through a programmable attentuator and compare to the signal of interest.  You can measure the strong signal accurately and use a calibrated attentuator - so the problem is reduced to one of comparison (you may want to add synthetic noise too).

If you haven't read the relevant section of "The Art of Electronics" then do so, its a very place to start for practical issues.
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