You can go up and down a scale always on the same vowel in the same way you can do it with the other vowels try to really feel everytime that you close the vocal cords between each sound try to feel it and not only to hear it, don't just work with your ears but also the physical feeling in the same way I can stop the sound by closing the vocal cords so if I stop the sound by closing the vocal cords you get this do it several times in the same way you can go up and down on a scale 