how to calculate signal to noise ratio from the graph?

[sukhiray]

In my current project, I have read voltage signal from a periphera. the signal has significants noises even after filtering it.  So, to identify the  required data, I have averaged the signal. 

I have attached the file having a picture of graphs. In this graph, the recorded data is plotted in black line and average graph is plotted in red. Now, I have to calculate the signal to noise ratio to specify with this values of peak. How to do it?

[johnsold · Accepted solution]

Since your signal goes through zero, you need to be careful in how you define the signal to noise ratio.  For sinusoidal signals the ratio is defined as the RMS value of the noise (the total signal with the desired sinusoidal signal removed) divided by the RMS value of the sinusoidal component.

First I would subtract the averaged value from the raw signal.  The difference represents the noise.  Then you can define the signal to noise ratio.  An RMS calculation might work.  If you have a mathematical model for the desired signal, a fitting to that model might be useful also.

Lynn 

[sukhiray]

Thank you very much for your response.

I have subtracted the actual signal to get the noise value.

now I have both of them, the actual signal and noise signal. 

Now what to do to get the signal to noise ratio. I do not have any RMS model to fit. I have to do all calculation myself. Please give me the guide line for the calculations I have to do on it to get the snr.

[johnsold]

It really does depend on what the signal means or what produced it.

One thing to try is to just use the RMS.vi from the Mathematics palette, if your data is an array or the Basic Averaged DC-RMS.vi from the Signal Processing >> Waveform Measurement palette.  USe two copies of the VI, one for the averaged signal and one for the noise.  Then divide.

Lynn