General > General Technical Chat
FFT and 60 Notch filter software
loop123:
--- Quote from: BrianHG on March 13, 2024, 06:23:52 am ---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?
--- End quote ---
Thats bec the source is the Netech EEG simulator which produces 10uV, 50Hz output into the amplifier which is set at 1000Hz bandwidth. What is the origin of the noises at each waveform? No I didnt inject any filter algorithm. It is directly from the BMA-200 amplifier to the E1DA ADC (the world highest performing 32 bit ADC) and direct to Audacity. The ambient AC capacitive coupling in the location is 60Hz. Are the noises harmonics? Pls break it down into the fourier component FFT style and recover the 10uV, 50Hz input. I want to see examples how you fix it.
Karel:
Synchronize the sampleclock of the ADC to the powerlinefrequency e.g. using a PLL.
That makes it way easier to remove the powerline interference (including harrmonics).
https://www.mainsfrequency.com/
loop123:
First, please tell me what exactly are these noises? In the 2nd image, they don't look like harmonics:
If they are harmonics. They should be resultant in the waveform. But my audacity waveforms don't show any resultant. The noises are riding in each part of the sine wave. How do you differentiate between EMI, RFI, amplifier noise, and quantization ADC noises? How sure are you they are powerline noises or harmonics? Please tell me what exactly those are first.
loop123:
--- Quote from: Karel on March 13, 2024, 07:29:54 am ---Synchronize the sampleclock of the ADC to the powerlinefrequency e.g. using a PLL.
That makes it way easier to remove the powerline interference (including harrmonics).
https://www.mainsfrequency.com/
--- End quote ---
I talked to the designer of E1DA. Ivan said:
Well. Ivan is a Russian electronics wizard. If he could say that. How can I even counter it. Ok. Someone please give an actual example how to filter the waveforms in the file I sent 2 messages prior. Please do it directly using your Apps, then I'll filter hundreds of other inputs myself after you actually showed the filter output by actually running it in your software. Thanks.
Karel:
--- Quote from: loop123 on March 13, 2024, 10:39:58 am ---
--- Quote from: Karel on March 13, 2024, 07:29:54 am ---Synchronize the sampleclock of the ADC to the powerlinefrequency e.g. using a PLL.
That makes it way easier to remove the powerline interference (including harrmonics).
https://www.mainsfrequency.com/
--- End quote ---
I talked to the designer of E1DA. Ivan said:
(Attachment Link)
Well. Ivan is a Russian electronics wizard. If he could say that. How can I even counter it. Ok. Someone please give an actual example how to filter the waveforms in the file I sent 2 messages prior. Please do it directly using your Apps, then I'll filter hundreds of other inputs myself after you actually showed the filter output by actually running it in your software. Thanks.
--- End quote ---
That's because your samplerate is not an integer multiple of the powerline frequency.
I thought we were talking about EEG and/or EKG here and you could select the samplerate.
If your application is about recording audio, then it's much easier to get rid of powerline interference (compared to EEG/EKG)
but you need to pay attention to grounding.
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