General > General Technical Chat
FFT and 60 Notch filter software
loop123:
--- Quote from: Andy Chee on March 12, 2024, 02:15:17 am ---
--- Quote from: loop123 on March 12, 2024, 01:19:50 am ---From the file, can you tell if the noise is external or in the circuit??
--- End quote ---
Are you only measuring one channel/electrode, or multiple channels/electrodes? Your photo only shows one waveform, so I'm assuming you're only measuring a single channel/electrode.
If you measure multiple electrodes, you can mathematically remove the common noise. The theory is that the skin potentials will be different at each electrode, but the noise (particularly 60Hz and other EMI) will be the same in all channels.
EEGlab can do this multiple channel common noise reduction, and I'm pretty sure Audacity should be able to do it with two channel stereo. The key is that you need multiple channels, not single.
--- End quote ---
Sorry. The following audio attachment (at bottom) is the file showing the distortions in the 10uV, 50Hz signal input, you have to zoom in the amplitude at Audacity or other editors to see them. I used single electrode pair connected to the Netech EEG simulator as shown in photo. My concern is the waveforms are distorted and even after I shielded the entire Netech and connector box. I still got distortions. So I just want to see the Fourier breakdowns of the waveforms to see what is the component frequencies causing the interference (if it is external or in the circuit). Please try loading it in Audicity and let me know. Your description about using multiples samples is a separate task. Remember at 30uV and higher, no distortions. only in the 10uV which happens to be the region I'd focus in.
Andy Chee:
--- Quote from: loop123 on March 12, 2024, 03:23:19 am ---
--- Quote from: Andy Chee on March 12, 2024, 02:15:17 am ---
--- Quote from: loop123 on March 12, 2024, 01:19:50 am ---From the file, can you tell if the noise is external or in the circuit??
--- End quote ---
Are you only measuring one channel/electrode, or multiple channels/electrodes? Your photo only shows one waveform, so I'm assuming you're only measuring a single channel/electrode.
If you measure multiple electrodes, you can mathematically remove the common noise. The theory is that the skin potentials will be different at each electrode, but the noise (particularly 60Hz and other EMI) will be the same in all channels.
EEGlab can do this multiple channel common noise reduction, and I'm pretty sure Audacity should be able to do it with two channel stereo. The key is that you need multiple channels, not single.
--- End quote ---
I used single electrode pair connected to the Netech EEG simulator as shown in photo.
Your description about using multiples samples is a separate task.
--- End quote ---
It's actually not a separate task, all the channels can be done all together. Noise removal is performed on all channels simultaneously, not individual channel one-by-one.
loop123:
--- Quote from: Andy Chee on March 12, 2024, 05:53:32 am ---
--- Quote from: loop123 on March 12, 2024, 03:23:19 am ---
--- Quote from: Andy Chee on March 12, 2024, 02:15:17 am ---
--- Quote from: loop123 on March 12, 2024, 01:19:50 am ---From the file, can you tell if the noise is external or in the circuit??
--- End quote ---
Are you only measuring one channel/electrode, or multiple channels/electrodes? Your photo only shows one waveform, so I'm assuming you're only measuring a single channel/electrode.
If you measure multiple electrodes, you can mathematically remove the common noise. The theory is that the skin potentials will be different at each electrode, but the noise (particularly 60Hz and other EMI) will be the same in all channels.
EEGlab can do this multiple channel common noise reduction, and I'm pretty sure Audacity should be able to do it with two channel stereo. The key is that you need multiple channels, not single.
--- End quote ---
I used single electrode pair connected to the Netech EEG simulator as shown in photo.
Your description about using multiples samples is a separate task.
--- End quote ---
It's actually not a separate task, all the channels can be done all together. Noise removal is performed on all channels simultaneously, not individual channel one-by-one.
--- End quote ---
What I want to determine for now is whether the noise is caused by EMI or the amplifier not capable of 10uV as Ataranov remarked. Bec even if I spent $3000 on human size Faraday cage. The distortion would still be there if it is the amplifier that has problem. If thats the case, then have to dive and spent $5000 on USBamp software and actives if it is the only means of last resort. So how do you know if the distortion is really caused by EMI or the amplifier just not capable of handling 10uV even if the amp used is the 5nV/sqrt(Hz) noised AMP01?
I just want to know the frequencies involved in the distortions for now and not about eliminating them right away.
BrianHG:
--- Quote from: loop123 on March 12, 2024, 06:04:56 am ---
What I want to determine for now is whether the noise is caused by EMI or the amplifier not capable of 10uV as Ataranov remarked. Bec even if I spent $3000 on human size Faraday cage. The distortion would still be there if it is the amplifier that has problem. If thats the case, then have to dive and spent $5000 on USBamp software and actives if it is the only means of last resort. So how do you know if the distortion is really caused by EMI or the amplifier just not capable of handling 10uV even if the amp used is the 5nV/sqrt(Hz) noised AMP01?
I just want to know the frequencies involved in the distortions for now and not about eliminating them right away.
--- End quote ---
Oh, so you must be doing your tests somewhere along Salaberry Blvd in Dollard Des Ormeaux / or in Kirkland...
Good luck, you will never get rid of that interference in that area of town.
loop123:
So in Audacity Frequency analysis, the frequency sides are being displayed. I want an app that can see the components (inside in illustration) in the following. What is the software called?
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