Replies

1. Expert Member
   BILL WICHERS | Mar 07, 2021 11:30pm | #1

   "Ultrasound" implies frequencies above the range of human hearing, which means above 20kHz. I doubt any phone would be able to detect frequencies that high, certaintly not with any sensitivity. Due to the need for filtering ahead of the analog to digital converters in the phone to deal with aliasing, the phone will have low-pass filtering that would limit, and likely prevent, any app from doing anything much above the range of human hearing. You typically need specialized equipment to reliably measure high frequencies -- especially with any accuracy. I have a sound pressure level (SPL) app for my cell phone, for example, and it's close, but not accurate, and that's tested against professional level equipment.

   When making measurements of things in uncontrolled enviornments in general, which is basically what you're doing if you're measuring in various places like you are, there is a basic rule to keep in mind: if you see the same problems everywhere, then the "problem" is usually an issue with your measuring equipment, not something that you're actually measuring. If you see the same pulses at the same frequencies everywhere you go, then you are almost certainly seeing some kind of artifact or error with your phone and/or the phone app, or possibly your phone itself is generating the sound. Even 20kHz is low for typical switch mode voltage regulators a phone would use (they usually run in the hundreds of kHz or higher, which allows for smaller and lighter weight electronic components to be used), but I suppose something else could be going on.

   Nothing uses sound for a power supply. Smart meters usually use either an RF (radio frequency) communications system, or carrier current, which is like AM radio carried on the power line wires. None of it is audible.

   Anything talking about "dirty electricity" is immediately suspect -- "dirty electricity" is pseudo science. There has always been noise superimposed on electric signals, it's been that way forever. Most of the noise is naturally occuring. You can, for example, detect lightning anywhere on the earth (look up "Schumann resonance" for more info on this). There is also galactic background signals up into the microwave region. It's not anything to worry about.

   I read the link about that app. Oversampling to read high frequency signals is possible, but not with a low-pass filtered front end like is present in a phone. Oversampling relies on very precise timing between samples so that higher frequencies than the nyquist limit can be measured with relatively low sampling rates. Tektronix built early digital oscilloscopes that way, although modern ones just sample at high frequencies so they don't need to use oversampling tricks. Oversampling can miss things.

   I don't think I have a transducer than can reliably reproduce sound at higher than maybe 22kHz frequencies or I'd download the app and test it's claims for you -- I have suitable professional signal generators in my lab that could easily generate the signals electrically, I just don't normally work with audio so I don't have anything to convert the electrical signals into sound.

   The short answer is that you have likely been "detecting" a problem with your measurement tool -- either an issue with the app, the hardware of the phone itself, or your phone is actually the source of the noise you're detecting.

   Bill

1. 
   Trevor_Lambert | Mar 07, 2021 11:56pm | #2

   Further evidence that the readings are not real is that 7kHz is well within the audible range. (20kHz is theoretically in the range as well, but most people can't hear it and the minority than can don't hear it well). If there was a significant amplitude of that sound you wouldn't need a phone app to detect it; you'd hear it loud and clear. For it to be one of the dominant frequencies, as the app is indicating, it would be louder than all the other background sounds that you can legitimately hear with your ears.

2. 
   user-2310254 | Mar 08, 2021 10:38am | #3

   Donna,

   Have you ruled out tinnitus? My wife has it and "hears" a constant loud buzzing and humming sound at all times. It's a maddening condition.