How to measure SNR of an EMG Signal?

hi
i want to measure SNR (Signal to Noise Ratio) of an EMG signal. I have attached a VI. Please have a look in the front panel. Among the three XY-graph, one is EMG, 2nd one is ECG and last one is EMG+ECG. I want to measure SNR for the signal EMG+ECG. Here ECG should be considered as noise. How to do so? I didn't find any convenient way for this. Please help me out.
Thanks at advance-
Taslim
Attachments:
SNR-1.vi ‏140 KB

Taslim,
Typically signal to noise ratio is defined on simple signals such as sine waves. Even if you have a "clean" version of the ECG signal, you cannot simply subtract or divide it because it will have a a slight phase shift and probably a small difference in the waveform due to the separation of the ECG electrodes from the EMG electrodes.
The SINAD VI in the Signal Processing >> Waveform Measurements palette uses FFT methods to identify the fundamental frequency and to isolate that "signal" from other components in the total signal.
With a signal which looks much like noise (the EMG) you must define exactly what you mean by signal to noise ratio and how it could be measured.
You might be able to take the RMS of the composite signal and compare that to the RMS of a clean ECG, but you would need to normalize the amplitudes in some way to make the result reproducible and meaningful.
Lynn

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Here are 2 other forum posts that had good responses about SNR and VIs that can be used to take the measurement:
http://forums.ni.com/t5/LabVIEW/Signal-to-Noise-Ratio-SNR-measurement/td-p/99326
http://forums.ni.com/t5/LabVIEW/how-to-calculate-signal-to-noise-ratio-from-the-graph/td-p/813558
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How to measure the baseline of a noisy, pulsed signal

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drawing of torque signal.gif ‏26 KB

Thanks for the reply. I understand what you are saying. However, I might have to modify my method for measuring the peaks if I choose to implement your idea. I have taken a screenshot of my "peak finder" code and attached it.
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Attachments:
peak_find_screenshot.jpg ‏45 KB

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Attachments:
Results_Waveforms.doc ‏141 KB

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http://sine.ni.com/apps/utf8/niae_asc.main
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Message Edited by kuroshio on 07-11-2005 10:49 AM
Message Edited by kuroshio on 07-11-2005 10:55 AM

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