So it can be found everywhere, the overtone. In everyday speech, coffee machines, cars, streetcars and, of course, in music, according to Lubbe in his further explanations. We all produce a variety and vast quantities of overtones every day - we are just not aware of them and have not learned (or forgotten) to hear them.
Hearing is also the primary issue when learning overtone singing. Specialist Lubbe, who taught himself overtone singing through years of trial and error and listening, would have "not much to say" to an overtone student. He admits this himself with an almost apologetic attitude. "It's not about how do I sing overtones, but how do I hear, how do I recognize my own overtones. And that's the principle."
But of course there is a basis from which you can start, and that is open vowels (O, U, A, E, I, Ö, Ü, Ä) on the one hand and a resonant fundamental tone on the other.
The word WOW is particularly suitable for starting out and trying it out for the first time. After practicing a few times, it could sound like this, for example: