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Silly tread
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ebastler:

--- Quote from: 001 on November 29, 2018, 07:10:17 am ---
--- Quote from: ebastler on November 29, 2018, 06:41:24 am ---I took a quiet section of the signal, which mainly has the high-pitched noise, and Fourier-transformed it via Audacity. The dominant tone is pretty exactly 5 kHz.

--- End quote ---
Thanx! Awesome help  :-+ What about its nature?

--- End quote ---

The signal looks pretty sinusoidal in the time trace, and the spectrum does not show significant harmonics at 10 or 15 kHz. Can't get more info from the recording, I'm afraid.

Others have mentioned switch-mode power supplies as a likely cause. Possible -- although I thought that these are mostly designed to use a switching frequency above the audible range? (To avoid problems like the present one, and also directly audible transformer squeal?)
001:

--- Quote from: ebastler on November 29, 2018, 07:17:42 am ---The signal looks pretty sinusoidal in the time trace, and the spectrum does not show significant harmonics at 10 or 15 kHz.

--- End quote ---

Is it some internet wire or other communication gear?
ebastler:

--- Quote from: 001 on November 29, 2018, 08:33:39 am ---
--- Quote from: ebastler on November 29, 2018, 07:17:42 am ---The signal looks pretty sinusoidal in the time trace, and the spectrum does not show significant harmonics at 10 or 15 kHz.

--- End quote ---
Is it some internet wire or other communication gear?

--- End quote ---

What I have not tried yet is to bandpass-filter your recording, to see whether it is a 5 kHz carrier modulated in some way. I can give that a try when I am back home tonight. But it does not seem likely; 5 kHz is just too low a frequency for information transfer in today's world...
SiliconWizard:

--- Quote from: ebastler on November 29, 2018, 07:17:42 am ---
--- Quote from: 001 on November 29, 2018, 07:10:17 am ---
--- Quote from: ebastler on November 29, 2018, 06:41:24 am ---I took a quiet section of the signal, which mainly has the high-pitched noise, and Fourier-transformed it via Audacity. The dominant tone is pretty exactly 5 kHz.

--- End quote ---
Thanx! Awesome help  :-+ What about its nature?

--- End quote ---

The signal looks pretty sinusoidal in the time trace, and the spectrum does not show significant harmonics at 10 or 15 kHz. Can't get more info from the recording, I'm afraid.

Others have mentioned switch-mode power supplies as a likely cause. Possible -- although I thought that these are mostly designed to use a switching frequency above the audible range? (To avoid problems like the present one, and also directly audible transformer squeal?)

--- End quote ---

Yes, but switching PS emissions are usually modulated by the current draw of the powered circuit, and that modulation itself can be in the audio spectrum. That's very common.

The fact there is not significant harmonics of the 5 kHz signal may be explained by the fact that most guitar preamp stages low-pass filter at between 5k and 10k usually.
001:
But why 5kHz?
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