Just curious- What is the signal I'm seeing
DashBarkHuss
Chicago
Hi, I'm not having any problems as this noise goes away with a filter pretty well. I'm just curious what it is.
When I turn off all notch filters and band pass filters* and then I hold the end of my computer charger in my hand while i'm wearing electrodes (lateral eog) I see this consistent pattern:
1 second
The little waves look like 60hz from the AC power grid. But what is that slower 5hz "envelope"- bead like shapes that the 60hz waves compose via their changing amplitudes?
*there's no way to actually turn the bandpass filters off so i set it to 0-5000hz
Comments
Dash, hi.
As you have concluded, the 60 Hz mains noise is absolutely HUGE and swamps out all biosignals. This is why we use bandpass AND notch filters together. The AC is so strong, that it forms 'harmonics' with other items in the environment. AC/DC power supplies used by computers and phones, have a complex assortment of electronics, such as 'switching power supplies'. These generate a wide bandwidth of noise components, including the 60 Hz primary frequency.
https://en.wikipedia.org/wiki/Switched-mode_power_supply
https://www.google.com/search?q=switching+power+supply+noise+characteristics
If you look at your signal with the FFT widget, you may be able to pick out some of the harmonic components.
https://www.google.com/search?q=wikipedia+harmonic+noise
Regards, William
Thanks @wjcroft. I wish there was a like button here so I didn't have to spam to say Thanks.
Thanks for the thanks! Switching power supplies have been a boon for electronics. But they certainly have added more 'noise' to the electromagnetic environment.
Gemini AI has some good info and links on this query:
https://www.google.com/search?q=are+some+switching+power+supplies+poorly+designed+and+emit+more+noise+than+they+should?
As just one example, super cheap poorly designed "LED light bulbs" are notorious for this, because the components are so tightly packed and the long-term heat degrades components.