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50 Hz noise ECG filtering using FFT and its inverse in LabVIEW

I have to write a LabVIEW Program to put the 50 HZ noise in the ECG spectrum using the FFT and then with the Inverse of the FFT I must take it out,but without using any if anybody can help me with that, I will be thankful.
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Your explanation was not very clear. Are you trying to add noise to a signal, remove the noise, or both. Please explain in more detail what you are trying to do.
Randall Pursley
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I have a normal EGG signal,and its Spectrum. Then I add the 50 Hz noise.In the Spectrum I will get this long peak at the x-axis at 50Hz.So,what I'm trying to do with LabVIEW, is to get out this noise without using a filter,but with the FFT and of course with its inverse to reconstruct the signal.
(the EGG signal is created at first with a simulator and not with human body, the signal is going through the "line-in" of the soundcard in the computer)

I hope you understand a little bit what I mean, I will attach what I did in the program till now,maybe you can understand it better.

Thank you

Message Edited by b_rani on 05-18-2005 01:46 PM

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What you would do is after applying the FFT multiply by a window that zeros out everything above a set frequency (in this case 40 Hz) and then do an inverse FFT. This will remove the noise.

See the attached file. The data I have loaded into the top graph has some 60 Hz noise on it that I filter out.

Don't forget, you are still filtering. Filtering is a convolution in the time domain and multiplication in the frequency domain.
Randall Pursley
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