So I have a pair of Bose noise-cancellation headphones that I plug into my keyboard every night to charge them (via my keyboard's USB port). My keyboard happens to be a metallic Apple keyboard. You will see why this may be important to note later.
Over time, I noticed a certain dull, electrical buzzing sound in my right earbud which occurred when I turned the noise-cancellation on. This buzzing sound was not constantly there. It would randomly appear for arbitrary periods of time and then vanish. It wasn't loud either, but it was loud enough to be noticeable and annoying.
For the longest time, I had no clue why this would happen. Sometimes the earbud would be perfectly silent (as it's supposed to be)… and then a buzzing noise would come out of nowhere. This was incredibly annoying and my only remedy was to listen to loud electronic music which blended in with the buzz and made it relatively unnoticeable. Of course, listening to almost any other kind of music proved annoying since my earbud would randomly, intermittently buzz at me.
Finally, one day, I noticed that when I touched my Android phone, the buzzing sound would increase in volume. I thought at first that this was due to my bodily position somehow stretching the wire, but with further testing I confirmed that my Android phone was the culprit. I slowly discovered that touching different objects, even when the headphones were not plugged into the speakers, would result in volume changes of this buzz.
One thing I noticed was that touching the headphone jack, whilst touching the Android phone that increased volume, would silence the buzz. With further testing, I noticed that touching my metallic keyboard would also silence the buzz, even whilst touching the Android phone or under any other circumstance in which there was a buzz.
I finally realized that my body is somehow conducting electricity when touching objects such as my Apple keyboard, headphone jack, or Android phone and that these are all related to the annoying buzz and nullification thereof. I found this bizarre and fascinating.
Ever since this discovery, I've found that I can silence this annoying buzz by pressing any of my fingertips on my metallic keyboard. This is also annoying, since it can make typing awkward to continually have one finger pressing against the metallic part. Nonetheless, I have no idea why this works at all; I suspect it might have something to do with my usage of the keyboard to charge the headphones via its USB port every night, but I have no substantiation of this hypothesis.
So my question is twofold:
- How does this bizarre phenomenon work wherein my body is apparently conducting electricity from objects which somehow control some anomalous buzz in my headphones?
- And how can I make this buzzing sound stop without keeping my body in contact with those objects? Obviously, I can't hold the headphone jack and listen to anything at the same time, and this habit of touching the metallic part of my keyboard is not great for typing nor my wrists which already suffer from CTS.
Any insight is appreciated.
Best Answer
The "buzz" is almost certainly RF pickup. This can be the mains (low frequency, 50/60/100/120Hz, unlikely in this scenario given a phone is involved) or rectification of the carrier frequency of the phone - remember how old tape players would make a "duh duh, duh duh" sound whenever a text message is received.
Human bodies are conductive. When your skin is dry you are about 100kOhm to 1MOhm. When your skin is wet, that goes down to about 10kOhm to 100kOhm. So there is nothing unusual about becoming a conductor.
As to why touching a metal keyboard kills the hum, or even touching the headphones jack. Basically as you are a nice large conductive area. When connected either to earth (e.g. via the keyboard shell and PC) or to the ground of the phone (e.g. headphones jack), you are basically changing how your body is interacting with the electric fields around you.
EMI is a dark art - it's hard to say exactly what current path you are interrupting, or how you are interacting with the fields. But generally if you ground yourself it stops you acting as an antenna - sort of like shorting yourself out.
One simple option you could try is to buy an anti-static wristband. That would allow yourself to be connected to earth (or to your keyboard) without having to touch the keyboard. Alternatively you could try simply charging your phone from something other than your keyboard to see if that stops noise injection.