During a studio recording, I heard a beep and paused the recording. I played it back and neither the actress, sound technician, or assistant director could hear it. I imagined that it could be the remote control unit of the air conditioning, which was turned off but still listening.

Listening to the tapes, I heard it again and found it in the frequency spectrum:

frequency spectrum

It is very, very faint, so here is the same picture with gamma correction and a note on the beep:

frequency spectrum, adjusted

Here is the recording.

I asked a musician and he didn't hear it either. I did frequency repair and it almost worked; doing it on the voice as well made it sound tinny. If I delete all frequencies above 6k, the voice sounds muffled; if I delete frequencies below, the voice becomes unintelligible. At 6k, it should be well within the frequency range of a human ear:

Frequencies capable of being heard by humans are called audio or sonic. The range is typically considered to be between 20 Hz and 20,000 Hz.

Why can I hear this beep sound and several people cannot?

  • Are you member of the K-9 family?
    – Alaska Man
    Commented Aug 8, 2020 at 21:43
  • @AlaskaMan What is the K-9 family?
    – emonigma
    Commented Aug 10, 2020 at 9:34
  • k-9 is American slang for 'canine' i.e. a dog.
    – Hobbes
    Commented Aug 11, 2020 at 6:41
  • 1
    Lol! No, I'm a real human curious about a newly discovered ability. That also explains trouble sleeping at night...
    – emonigma
    Commented Aug 12, 2020 at 9:55

1 Answer 1


I listened to the file several times and couldn't hear it. In a spectrum analyzer, I can see what you're referring to. It's at -90 dB, so you'd have to crank up the volume pretty far to be able to hear it.

Because the speech volume in the recording is at -20 dB, most people will set the volume to a level where that's comfortable to listen to, and the beep will disappear below the noise floor.

The spectrum indicates the sound is in a narrow frequency band (or even a single frequency), so you might be able to get rid of it with a very narrow notch filter.

enter image description here

  • Can you hear it if you increase the volume on that part only? I am also able to notice other background rumble when listening with volume at level comfortable for me and others cannot; does that simply mean that I have more sensitivity to background noise?
    – emonigma
    Commented Aug 8, 2020 at 10:23
  • Yes. I can also hear it if I listen to the unedited recording on my IEMs with the volume a bit above normal (doing this on my laptop, so can't say how much above normal).
    – Hobbes
    Commented Aug 8, 2020 at 10:43
  • It's entirely possible your hearing is more sensitive than others. You're probably also more used to how the studio and its equipment sounds than the others.
    – Hobbes
    Commented Aug 8, 2020 at 10:46
  • Thanks. This was my first time recording in studio. I was bothered by it and stopped recordings, so I got good alternate tape anyway.
    – emonigma
    Commented Aug 8, 2020 at 10:50

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