Calculating SNR for ECG signals I'm reading through the literature for finding the best way to calculate SNR for a ECG signal. While there are many algorithms for improving SNR, I couldn't find any that details any standard procedure for evaluating the SNR itself. The following are my questions.


What is the SNR of a typical ECG signal from the MIT/BIH database? What is considered a good SNR for a typical ECG signal?
http://www.physionet.org/physiobank/database/mitdb/
What would qualify as Signal and Noise for ECG? The assumption that I worked with is to apply a bandpass filter with cut-offs fc=[0.5Hz,45Hz] on the recorded ECG signal to get the Clean ECG signal, then subtract the clean ECG signal from recorded signal to obtain noise and then use the matlab snr function to evaluate  SNR with the clean signal and noise as arguments. But, in some papers it is recommended to reject everything except the QRS complex to get the clean signal. Is there any standard/recommended procedure for calculating SNR for ECG?
http://en.wikipedia.org/wiki/QRS_complex
What would be the best way to calculate ECG SNR in real-time in an embedded platform?
I don't know about real time application normally what I am doing is to calculate $\mathrm{PRD}$ first and calculate $\mathrm{SNR}$ from $\mathrm{PRD}$ 

$$\mathrm{SNR}=-20\log_{10}(0.01\mathrm{PRD})$$

$\mathrm{PRD}$ -  Percentage Root Mean Square Deviation