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FFT and 60 Notch filter software

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loop123:

--- Quote from: gf on March 13, 2024, 01:45:39 pm ---
--- Quote from: loop123 on March 13, 2024, 12:52:00 pm ---
--- Quote from: gf on March 13, 2024, 12:11:05 pm ---Is the .wav file supposed to contain any useful information?
Besides the spurs, everything looks like random noise to me :-//

--- End quote ---
It is just sine wave generator output of 10uV, 50Hz sine wave. Simple only but why is the output at Audacity has so much noise? Goal is simply to remove the noise and regain the pure 10uV, 50Hz sine wave. pls help do that.

--- End quote ---

My understanding was that the 50 Hz component (and the other spurs) are interfering signals which you want to suppress. If, OTOH, the 50 Hz signal is the useful signal you want to keep (while all the other spectral components should be suppressed), then this can easily be done with a narrow bandpass filter. However, I think this is not what you really want. A real EEG signal is not a pure 50 Hz sine wave, therefore such a bandpass filter would suppress most of the useful components in a real EEG signal. Is the EEG simulator not able to simulate a more realistic EEG signal?

--- End quote ---



Above is the specs of the Netech simulator I'm using. It can only output 0.1, 0.5, 2, 50, and 60 Hz.  I chose 50Hz signal. The amplitude choices are 10, 30, 50, 100, 500 μV, 1,2, and 2.5 mV.  I chose 10μV signal.  And I fed the 50Hz, 10uV signal into the BMA-200 bioamplifier. And connect the BNC output of the BMA-200 to the E1DA Cosmos ADC and into Audacity. 

Yes, 50Hz is the signal, not the noise. It's just to test the unit. So if 10uV, 50Hz sine wave is the signal. Why does Audacity show it with so many noises like in following? Are they harmonics? but where is the resultant in 2nd image?  This is only present if 10uV are used and not only higher amplitude signal which has better SN Ratio.






Please remove the noises and present the pure 10uV, 50Hz output from the Netech simulator.

loop123:

--- Quote from: Karel on March 13, 2024, 02:01:59 pm ---I opened your wav file in EDFbrowser and it doesn't look noisy.

--- End quote ---

The one you downloaded is the 2.5mV, 60Hz output from Netech Simulator. Instead download the attached one with 10uV, 50Hz signal from the Netech simulator.

I loaded at audacity now and the following is the waveform

gf:
That's what I get if I notch out 60Hz and 78 Hz and cut-off the bandwidth at 100 Hz. What bandwidth do you need to keep?
Audacity has notch and lowpass filters, too, so I guess you could do the same in Audacity.

loop123:

--- Quote from: gf on March 13, 2024, 03:18:40 pm ---That's what I get if I notch out 60Hz and 78 Hz and cut-off the bandwidth at 100 Hz. What bandwidth do you need to keep?
Audacity has notch and lowpass filters, too, so I guess you could do the same in Audacity.

--- End quote ---

Did you used my audio file above? I want to keep 1000Hz. I just ran EDFbrowser for first time and loaded it up but I can't find how to run the Amplitude FFT done by Karel. where to find it. He loaded  up the 2.5mV file, not the 10uV, 1000hz file which is in my last message. Please remove the noises and retain 1000Hz, 10uV.

WatchfulEye:
Most of the noise is between 50 Hz and 1000 Hz - it is broad band noise, not at any specific frequency.
Apart from the 60 and 78 Hz spurs, the only way to reduce the noise is reduce the bandwidth. You cannot keep up to 1000 Hz and reduce the noise any further with any simple filter process.

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