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FFT and 60 Notch filter software

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oPossum:
Band-pass filter.

You really seem to be 'in over you head' on this.

tggzzz:
Or he could look at p374 in https://www.worldradiohistory.com/UK/Wireless-World/70s/Wireless-World-1974-10.pdf and find an article "Mains Rejection Tracking Filter - using a tracking 'n-path' filter with wide dynamic range" to remove not only the fundamental but also the harmonics.

Not many people understand weird and wonderful n-path filters. I expect it would blow the OP's mind.

BrianHG:

--- Quote from: tggzzz on March 12, 2024, 06:44:33 pm ---Or he could look at p374 in https://www.worldradiohistory.com/UK/Wireless-World/70s/Wireless-World-1974-10.pdf and find an article "Mains Rejection Tracking Filter - using a tracking 'n-path' filter with wide dynamic range" to remove not only the fundamental but also the harmonics.

Not many people understand weird and wonderful n-path filters. I expect it would blow the OP's mind.

--- End quote ---
I completely forgot about that concept.  Yes, done right, you can eliminate the mains interference completely.  However, if loop123 is using his amp to read human biometrics, you have the problem that every time you re-wire to a new person in a different place, you may too radically change your source interference characteristics.

If loop123 has enough input channels, just sacrifice 1 channel as you mains reference noise channel.  Then, subtract that channel's signal from all your channels of interest and you will null out your main's noise.

It's basically how a differential line signal works.

loop123:

--- Quote from: BrianHG on March 13, 2024, 12:47:41 am ---
--- Quote from: tggzzz on March 12, 2024, 06:44:33 pm ---Or he could look at p374 in https://www.worldradiohistory.com/UK/Wireless-World/70s/Wireless-World-1974-10.pdf and find an article "Mains Rejection Tracking Filter - using a tracking 'n-path' filter with wide dynamic range" to remove not only the fundamental but also the harmonics.

Not many people understand weird and wonderful n-path filters. I expect it would blow the OP's mind.

--- End quote ---
I completely forgot about that concept.  Yes, done right, you can eliminate the mains interference completely.  However, if loop123 is using his amp to read human biometrics, you have the problem that every time you re-wire to a new person in a different place, you may too radically change your source interference characteristics.

If loop123 has enough input channels, just sacrifice 1 channel as you mains reference noise channel.  Then, subtract that channel's signal from all your channels of interest and you will null out your main's noise.

It's basically how a differential line signal works.

--- End quote ---

For now the input is a Netech sine wave simulator. In the following 10uV (microVolt), 50Hz source is used because the simulator only has 0.1Hz, 2Hz, 5hz, 50Hz, 60Hz setting. And I can't chose 60Hz because the Audacity notch filter can totally null all amplitude.

In the following, the BMA200 Amp has 1000Hz bandwidth selected. Enclose in it is the Frequency Analysis. How do you remove the noises? What noises do you call them? It is the same input as the original file but only now the Amp bandwidth has 1000Hz selected instead of just 100Hz. Attached is also the audio file. Please check using your FFT what noises are they comprised off. If I 60Hz notch filter it, the amplitude went down but the noises remain. Please try to find ways to remove the noises and share what you did. From the Frequency Analysis below, what frequencies are the noises? If they are harmonics, where are the frequencies of the harmonics located in the FFT. Thanks!





BrianHG:
Oh man, that 6.7khz tone in the .wav is maddening.  And I see a main dominant 50hz spike. There was a weaker 60hz and 80hz tones as well.  Are you sure this was recorded in north America?  Or, did you attempt some sort of filter algorithm which injected some fundamentals?

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