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FFT and 60 Notch filter software

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loop123:

--- Quote from: ataradov on March 11, 2024, 11:37:53 pm ---
--- Quote from: loop123 on March 11, 2024, 11:11:31 pm ---The waveform disappeared so it is not on at default.

--- End quote ---
I did not say it was on by default. This is not even how Audacity works, nothing is on by default. The workflow if such that you apply plugins. I said that the default value when you apply the filter is 60 Hz.



--- Quote from: loop123 on March 11, 2024, 11:11:31 pm ---When I tried Frequency Analysis. Why don't I get just a peak at 60Hz (or 50Hz), instead, it shows many frequencies up to 9kHz like the following.

--- End quote ---
Enable logarithmic scale for the frequency axis and increase the size of the FFT.

This is basic FFT stuff. If you can't figure that out at this point, you are not likely to get anywhere.
--- End quote ---

Done. So the other frequencies shown besides 60Hz is the noise floor?  What kind of application where it will only show the 60Hz and the component frequencies from Fourier breakdown of the frequencies actually displayed. This is what I want to see. Not the inclusion of noise floor or whatever the wide frequency in the plot.

tggzzz:

--- Quote from: loop123 on March 11, 2024, 11:46:36 pm ---
So the other frequencies shown besides 60Hz is the noise floor? 

--- End quote ---
No.

ataradov:

--- Quote from: loop123 on March 11, 2024, 11:46:36 pm ---Done. So the other frequencies shown besides 60Hz is the noise floor?

--- End quote ---
They are artifacts of the transform and quantization. You can apply different windowing functions and see how they change.



--- Quote from: loop123 on March 11, 2024, 11:46:36 pm --- What kind of application where it will only show the 60Hz and the component frequencies from Fourier breakdown of the frequencies actually displayed. This is what I want to see. Not the inclusion of noise floor or whatever the wide frequency in the plot.

--- End quote ---

You are looking at it at the result of the transform. You can extract the full information. There is an export button where it will save this information into the file and you can take whatever you need.

I don't understand what you want from it, so it is hard to tell what to do exactly.

loop123:
This is actually what I want. I inputted 10 microvolt 50Hz into the amplifier I always get this waveforms and not a uniform sine wave. I even enclosed the electrodes in metal box so it is shielded from capacitive coupling and intereference current. What I want to know is what is causing the interference such tha the waveforms are distorted and not pure 10uV 50Hz sine wave?

ataradov:

--- Quote from: loop123 on March 11, 2024, 11:53:24 pm ---I inputted 10 microvolt 50Hz into the amplifier I always get this waveforms and not a uniform sine wave.

--- End quote ---
What makes you think your source is a pure sine wave in a first place? Have you characterized your amplifier for noise and distortion?

You are working with very low levels and shitty electrical setups. Of course there will be all sorts of distortions.

I don't see how FFT would be of a lot of help here.

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