Those are called Alpenhorns.
Seen in Ricola commercials.
I’m not sure of what it is, but my daughter and I went through several of the Youtube videos in an effort to identify the sound. I have to qualify this by saying that my family is musically inclined. Several play instruments, several sing, and my grandparents/great grandparents were instrument makers. One made violins, the other made organs and tuned pianos. A good ear is a common gift in many family members.
And no, we aren’t experts.
If YOU have a good ear, you can try it for yourself.
Some of the ‘horns’ sounded like tubas, some like trombones, having the same pitch and quality. Some sounded like bass fiddles or chellos. Additionally comparisons were made with various shofars. None of the shofars that we listened to, matched any of the sounds. The most close match we could find were those really long tube things that they have in the Alps. I forget the name of those. We looked up instrument sounds and compared them to the youtube videos.
In the end, we decided that if these videos aren’t fakes, then it sounds like God is causeing the heavenly orchestra to do some practicing :)
But really...check out those mountain horns!
ALPINE HORNS......maybe?