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Is there anything that emits a high frequency that human ears can't hear yet would scramble digital voice recorder. Answered

As I'm a local chairman for a union. Sometimes an investigation isn't going as we would like it. And the company that employs us sets a portable voice recorder up so, that they can transcribe it at a later date. So my thought was if I could scramble or delete the recording somehow then everybody stays working. No harm. No foul, Right??? It may be wrong, but is it really. When you are trying everything you got to keep people employed, that have made an error or two on there job. Please Help. All the knowledge that you guys have brought forth so far is amazing. Thanks 



Best Answer 5 years ago

I would guess that you are trying to make a frequency that you couldn't hear while recording, but would over power anything recorded when played... right?

1. It is theoretically possible, I've just never heard of anyone actually figuring it out, and if they did, it would be more or less for one specific recording device... each has different frequency ranges and different distortions.

2. Just because the human ear can not hear the frequency does not mean that it can not cause damage. Every sound that is emitted has pressure even if you can not hear it. The pressure required for such a project would be a lot... and could cause damage to people's hearing... and could really drive your pets nuts. Literally. This is a question that a few people that I am aware of have worked on, but so far all they have is theories.  You would also have to take into consideration the inverse square law.  You might want to look into SPL, and who knows, this might be a good place to start.  (https://www.instructables.com/id/The-Concept-Of-Sound-Pressure-SPL/)

If you can't hear it live you can't hear it on a recording. You might be able to create what sounds like a little static but nothing that would destroy a whole recording. Unless you found the resonate frequency of the device and shook it to pieces.

Well, a recording (especially bad ones) change the frequencies, so in theory it is possible... I've just never seen it done and am not sure what frequency to use.

If the recorder had an AGC (automatic gain control) and the frequency response of circuitry up to the AGC could handle your high frequency signal then a loud, inaudible tone would then swamp the AGC so the recording gain would drop so low it would not 'hear' your speech.
More likely the recorder input is filtered to limit the response so this would not work.


The mic will only be so responsive, and a voice recorder will be filtered because less frequency response = easier to compress audio. If mp3, it already throws away the high and low frequencies. I doubt the AGC would ever hear the non-audible junk.

Assuming the mic could pick up the frequency you are shooting for it wouldn't effect the rest of the audio. Chances are if you could find such a frequency you wouldn't be able to get a speaker that could accurately reproduce it and at the level high enough to cause any damage to the recorder. Assuming you could find such a speaker and could play it load enough to damage the recorder it would likely cause damage to other things and people in the area. If your worried about being taped then do frequent sweeps of your area before discussing any sensitive issues.