General > General Technical Chat

FFT and 60 Notch filter software

<< < (13/18) > >>

Karel:

--- Quote from: loop123 on March 13, 2024, 03:24:41 pm ---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.

--- End quote ---

To view the powerspectrum of a signal, leftclick on the signallabel and choose "Spectrum".

https://www.teuniz.net/edfbrowser/EDFbrowser%20manual.html#Powerspectrum

BrianHG:
LOL, you could just apply a deep 3D statistical FFT noise remover algorithm.  (There is an 20 year old audio editor which can do it, but, I don't think its what you want since it requires example sample noise to work with, then it removes just that noise and leaves everything else automatically.  Though, it only supports 24bit integer sampling, maybe 32bit floats.)

However, since you have been delivered a simulated sample and not working with true hardware where you can make sure there is no 60hz/50hz noise from the source, you are working with someone who wants you to make your own specific filter for these EEG cases which you will not easily achieve.

NOTE: In real life, the 50hz/60hz over a 24 hour period is typically good, but from minute to minute, I've seen it drift up and down by as much as 0.2hz.  There have been recorded cases where the line frequency has been off by as much as 1hz or more.

tggzzz:

--- Quote from: Karel on March 13, 2024, 04:59:50 pm ---
--- Quote from: loop123 on March 13, 2024, 03:24:41 pm ---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.

--- End quote ---

To view the powerspectrum of a signal, leftclick on the signallabel and choose "Spectrum".

https://www.teuniz.net/edfbrowser/EDFbrowser%20manual.html#Powerspectrum

--- End quote ---

You had better tell him how to "leftclick", before he asks us.

BrianHG:
What you really need is to sample all the EEG channels in parallel.  Then, make an algorithm which subtracts the common noise from all the channels channels together leaving you with the pure EEG signals.  This means you need a 16 channel sampler with 16 channel amp and 16 channel capture software.

Remember, the 60hz/50hz/6.7khz noise will be on all channels, just at slightly different amplitudes and for the high 6.7khz, slightly different phase.  With all that source info, you can negate just the commonalities between channels.  No notch filtering.  This means a filter with no ringing, echo, bounce.  A filter which will also follow power interruptions and surges since the same junk will be present on all channels.  A notch filter may be useful as a selector to zero in on these selective frequencies, but for low frequencies like 60hz, with a 44.1khz sample rate, you will have a huge 65kpoint sample lag to teeth out that narrow band.

loop123:

--- Quote from: WatchfulEye on March 13, 2024, 03:50:12 pm ---Only the 60 Hz noise is powerline.

There is a mystery 78 Hz noise.

The main noise is broadband noise - which looks like noise floor, but by my calculations it is about 100-150 nV/sqrt Hz - much higher than specified noise of the AMP01. It could be noise from the waveform generator.

However, note that BMA-200 specifies 7uV noise - and your recording shows less noise than this.

You could try measuring the noise directly by using a 1 kohm resistor instead of the waveform generator. It would be interesting to have a series of recordings with different waveforms and 1 with just a resistor - all settings left exactly the same.

--- End quote ---

Edit: this is 30uV in the 2nd BMA instead of 10uV. With both set to 10uV. the noises are identical.



Anyway. Out of curiosity. Have you guys encountered an amplifier that has no obvious damage but the noise just became 20 times worse like from 5nV/sqrt (Hz) to 100 nv/sqrt (Hz)?

What about ADC. Can ADC damaged by ESD etc cause much more noises too and not obvious non-functional state? Because I have another unit, the expensive $16750 g.USBamp used by major R&D centers worldwide. I got it used for $1100. The following are the waveforms. At 10uV, 1000Hz, the waveforms have bad noises which I guess are not powerline noises at all but the noise floor itself? The g.USBamp doesn't have any amplifier, it uses ADC only with +-250mV range. It's noises are Noise level   < 0.4 µV rms 1-30 Hz. Extrapolating it to 1000Hz, I guess the noises would be above 1 uV? Yet the $16750 unit sells so much. I still haven't bought their $4000 software to use it fully so I used their demo software just to test it.

See its specs at

https://www.gtec.at/product/gusbamp-research/

The following are the outputs from USBamp demo (offset is adjusted to 100uV or it can go off the scale). Input all 10uV, 50Hz from the Netech simulator

The following with 100Hz bandwidth in the USBamp app with Notch Filter off:



The following with 100Hz bandwidth in the USBamp app with Notch Filter on:



The following with 250Hz bandwidth in the USBamp app with Notch Filter off:



The following with 250Hz bandwidth in the USBamp app with Notch Filter on:



The following with 500Hz bandwidth in the USBamp app with Notch Filter off:



The following with 500Hz bandwidth in the USBamp app with Notch Filter on:



The following with 1000Hz bandwidth in the USBamp app with Notch Filter off:



The following with 1000Hz bandwidth in the USBamp app with Notch Filter on:




Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod