What you see in this dynamic MRI recording of tongue movement in the vocal tract while doing overtone singing and normal singing. The positions of the tongue forms the resoncance cavities which delete all not-wanted overtones in the sound of the voice at a certain point in time, and then amplify a single overtone that is left, which can be heard as a seperate note above the fundamental.
The MRI recordings were made by Prof. Dr. Bernhard Richter, Prof. Dr. Matthias Echternach and Dr.- Ing. Michael Burdumy in the University Medical Center Freiburg, Institute for Musician’s Medicine. http://www.mh-freiburg.de/fim – thank you so much for the kind permission to use the MRI-footage in order to share this fascinating singing-insight with the world!
The team of doctors in Freiburg developed a highly specialized equipment for recording and and also filtering sound in the MRI-machine. This recording is made while using a pre-produced playback on headphones in the really loud MRI-machine while lying on the back.