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FFT and 60 Notch filter software

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loop123:

--- Quote from: Karel on March 13, 2024, 10:50:03 am ---
--- 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.

--- End quote ---

My amplifier target input is 10uV, 1000Hz with gain of 50000.  The output bandwidth is set at 1000Hz. So the output is 10uVx50000= 0.5V, 1000Hz.  The ADC is to record the 0.5V, 1000Hz.  What samplerate must I adjust in Audacity so I can filter the powerline frequency and harmonics? 

Karel:

--- Quote from: loop123 on March 13, 2024, 11:13:00 am ---
--- Quote from: Karel on March 13, 2024, 10:50:03 am ---
--- 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.

--- End quote ---

My amplifier target input is 10uV, 1000Hz with gain of 50000.  The output bandwidth is set at 1000Hz. So the output is 10uVx50000= 0.5V, 1000Hz.  The ADC is to record the 0.5V, 1000Hz.  What samplerate must I adjust in Audacity so I can filter the powerline frequency and harmonics?

--- End quote ---

Change the recording samplerate of your device from 44.1 KHz to 48 KHz which is an integer multiple of 60 (and 50) Hz.
Design a PLL controlled VCO that creates the clock for your ADC chip and synchronize it with the powerline frequency.
That gives you much more options to use sophisticated algorithms in order to remove the powerline interference.

But we can help you better if you tell us what you want to achieve. What is it what you want to measure? Audio? Something else?

WatchfulEye:

--- Quote from: loop123 on March 13, 2024, 09:46:05 am ---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.

--- End quote ---

You seem to be looking for an individiual frequency as the source of your noise/distortion. It actually appears that this is broadband noise/noise floor that you are seeing. Also, a hint when using the audacity spectrum viewer - you need to amplify the signal first, as the viewer has a fixed minimum on the Y axis. You can then magnify as required in the spectrum viewer.

This is the spectrum of the last waveform you posted. I've also calculated normalised amplitudes for narrow band noise, on the basis that the signal is 10 uV rms.

You can see the 50 Hz signal, and small 2nd and 3rd harmonics. You can also see a small amount of 60 Hz noise (1 uV), but no harmonics.
However, there are 2 unknown and more important noise sources - 78 Hz (1.7 uV) as well as harmonics of 78 Hz, and broadband noise (approx 100 nV/sqrt Hz).

The 60 Hz is likely coming from power line noise, and could be mitigated with better shielding, or the use of a notch filter (depending on the frequencies of interest in your signal), or differential measurement.
The 78 Hz is a mystery, and may be noise generated by the simulator.
The broadband noise may be the noise floor of your setup, and because of it's 1 kHz bandwidth, it has a total contribution of approx 3 uV.

I suggest repeating the measurements with other waveforms and amplitudes, to see what happens to the unknown noise sources. It may be that some of the unknown noise is from your waveform generator.

loop123:

--- Quote from: Karel on March 13, 2024, 11:23:03 am ---
--- Quote from: loop123 on March 13, 2024, 11:13:00 am ---
--- Quote from: Karel on March 13, 2024, 10:50:03 am ---
--- 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.

--- End quote ---

My amplifier target input is 10uV, 1000Hz with gain of 50000.  The output bandwidth is set at 1000Hz. So the output is 10uVx50000= 0.5V, 1000Hz.  The ADC is to record the 0.5V, 1000Hz.  What samplerate must I adjust in Audacity so I can filter the powerline frequency and harmonics?

--- End quote ---

Change the recording samplerate of your device from 44.1 KHz to 48 KHz which is an integer multiple of 60 (and 50) Hz.
Design a PLL controlled VCO that creates the clock for your ADC chip and synchronize it with the powerline frequency.
That gives you much more options to use sophisticated algorithms in order to remove the powerline interference.

But we can help you better if you tell us what you want to achieve. What is it what you want to measure? Audio? Something else?

--- End quote ---

Surface biopotentials of 10uV, 1000Hz. Experimenting on bionics implants. It will be difficult to "Design a PLL controlled VCO that creates the clock for your ADC chip and synchronize it with the powerline frequency.". Who has actually built them?  can you guys just do it on existing software? are you saying no software can even filter them? but pls answer 2 messages prior what those noises are in the first place bec they seemed not to be harmonics owing to lack the resultant as shown in the figure.

tggzzz:

--- Quote from: loop123 on March 13, 2024, 11:41:52 am ---Surface biopotentials of 10uV, 1000Hz. Experimenting on bionics implants. It will be difficult to "Design a PLL controlled VCO that creates the clock for your ADC chip and synchronize it with the powerline frequency.". Who has actually built them?  can you guys just do it on existing software? are you saying no software can even filter them? but pls answer 2 messages prior what those noises are in the first place bec they seemed not to be harmonics owing to lack the resultant as shown in the figure.

--- End quote ---

For medical electronics, especially implants, it is essential that you use hardware designed for such purposes in a way specified by the manufacturer.

Any homebrew hardware or hardware operated in a system not designed for medical purposes may be a safety hazard. The tone of your repeated questions makes me doubt that you are qualified to design and/or operate such hardware. Hence be very careful of the consequences of your actions and inactions. Consult the terms and conditions of relevant professional insurance policies, looking to see whether you might be personally liable.

If the digitiser has adequate dynamic range (see the ENOB specification) and higher than necessary sampling rate, then downconverting to any lower rate is a standard DSP operation with well known consequence. Consult any DSP textbook, and use DSP software. Do not expect standard audio hardware and software to be sufficient.

Wrtng sntncs like this mks u lk unprofessional.

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