It's the discontinuities where the 20 kHz bursts start and stop.
Any discontinuity results in a wideband click similar to an impulse. The portion falling in the audible frequency range is, well, audible. Blame Mr Fourier.
Ah ok it's Fouriers fault. It would be cool if someone could explain this in words.The Problem is i have no clue about fourier transforms and math harder than ±×÷.
"...Limiting case: a unit impulse of a width that approaches zero time has a frequency spectrum that includes all frequencies..."
Can understand this like this jumps are like a pulse that include a lot of frequencies. The shorter the time the more frequencies included?
Exactly.
Ok, thx this explains why you can hear them also in a woofer?
Yes. Let's say the burst is repeated four times a second. Then you'll get components at 4, 8, 12, 16, 20... Hz, definitely in woofer territory.
And here's how it could/should have been…
I'll leave it to you lot to work out what I've done Up yours, Monsieur Fourier!
p.s. I've deliberately left the really big click in there
I haven't the time to check, but I wonder to what extent your original file contains frequencies above Nyquist i.e. as though a suitable anti-aliasing filter had not been used?But i try to understand what happens with that click
I haven't the time to check, but I wonder to what extent your original file contains frequencies above Nyquist i.e. as though a suitable anti-aliasing filter had not been used?
A useful rule of thumb in audio editing; no transition less than 5mS!
but the clicks are what i like to understand.
Maybe the sonogram of the file can help you :
View attachment 68482
What we hear are the vertical blue bars.