# I have a noisy ECG Signal. want to use PSD to analyse the Signal to noise ratio

I have a really noisy ECG Signal which contain, motion artifacts,muscle noise, a very high amplitude noise.

I am beginner to DSP. Can someone tell me in a simple language,how do i interpret the signals feature when i get this kind of image. samping frequency is 1000hz. i used psd.welch in matlab.

Why it is plotting against only 500hz and what information i can get on this

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Can you attach the image please? – Atul Ingle Sep 7 '12 at 15:26

• Plotting against $500Hz$: Because that is the frequency of the sampled signal. We usually sample a signal at least two times of its max frequency in order to avoid aliasing. In your case $fs=1000Hz$ (sampling frequency), so max frequency is (no higher than) $500Hz$.
• The information you can get: Which frequency corresponds to high powers. You can avoid power below $0$ frequencies. High frequency components are usually our signal while low power is noise.