I tried with several random sounds, using Unmix Song
Yes, there appears a spike at around 14.700 Hz, reproducable.
This seems just like another algorithmic glitch in SL.
After using SL for over a year now, I do not trust SL in any scientific way. It’s a nice toy, but in no way realiable for usecases, which require exact precise operations beyond artistic purpose.
I love the concept of SL, but the actual implementation leaves a lot of questions, at least to me.
Maybe there are some kind of frequency cuts in the quality settings of the algorithms, which seems plausible.
But(!) this should be documented somewhere. The documentation lags lots of information of what is going on under the hood. Especially all the parameters around FFT are a mystery. This might be, because a lot of people have some kind of fear about mathematics, but not all of them.
It should be clear, that somehow sometimes, there are people, who check the program rigorously and discover glitches and bugs, that for many are either not noticable or worth to follow - understandable, of course. But unsatisfactory on the other side.