High pitch noise: how to fix and how to prevent

I record a podcast over Zencastr. My podcast partner uses a USB headset with a laptop. Recently, I noticed a strange high pitch that appears mostly when the partner is silent. The attached file is an example of such noise. My questions are: 1) what might the cause of this noise be and how to prevent it and 2) how to remove it from a recording?

It sounds like electrical interference from somewhere.

You can filter it out by applying a notch filter 5 times at frequencies of 2000, 4000, 6000, 8000, 10000 Hz. I’d suggest setting “Q” to about 8.

MosquitoKiller4.ny” plugin on 8 gets rid of most of it.

But 4kHz & 6kHz are particularly strong so require additional treatment …

@steve, you are very particular about the numbers. Are these numbers characteristic of this type of noise, or did you get them from analyzing the file? If latter, can you please tell me how to do this analysis by myself?

Track spectrogram view (Spectrogram View - Audacity Manual)

Notice the two horizontal dashed lines at 4kHz and 6 kHz.

After amplifying the track, the lines at 2, 8 and 10 kHz are also visible:

These sounds are also visible in “Plot Spectrum” (Plot Spectrum - Audacity Manual) if you look closely:

In answer to the other question, this kind of noise can happen when the microphone doesn’t get along with the USB service it’s connected to. A USB connection is supposed to supply clean, pure 5 volts from the computer to the microphone to accept sound from the performer and convert it into data. The data then goes back down the cable to the computer. It’s pretty common for the computer to be a little sloppy with the 5 volts and there can be a little data leaking here and there. It’s expensive to filter 5 volts and most people don’t care.

This is the “Let the microphone worry about it” theory.

Scene shifts to the microphone which uses the 5 volts from the computer to amplify the super tiny, delicate voice signal to be large enough to turn into data for shipment to the computer. It depends on the computer delivering clean, pure 5 volts because having the microphone filter it is expensive.

This is the “Let the computer do it” theory.

The problem comes when nobody does it and your high-pitch whine is what happens when computer trash leaks into the voice. I used to call this the “Yeti Curse” because millions of people bought the insanely popular Blue Yeti microphone and a fraction of those people (the ones with sloppy computers) turned up with this whine sound and complained about it on the forum. It sounded like frying mosquitoes, so Mosquito-Killer is the name of the plugin.

Mosquito-Killer4.ny (363 Bytes)
The fourth version, I believe is current. I can’t find the author information and there’s none listed in the code. In this case, the problem is so acute that additional filtering is needed. We tried. There is no simple, cheap cure. The only permanent cure is get rid of the computer, the microphone, or both.


Thanks a lot

There’s another note about this noise, too. It violates the ACX Audiobook background noise specification. If you have well-behaved microphone noise (gentle rain in the trees ffffffffff) and you can get it quieter than -60dB, then you’re good to go (although in practice you have to hit at least -65dB).

Yeti Curse noises fall into a sensitive area of your ear (baby screaming on a jet) and they’re hard to deal with, and so the Frying Mosquitoes filter was designed.

Hard-wired USB systems tend to have steady tones—not flipping in and out. Does your partner have any wireless or bluetooth devices?