The best website I know of on Tuvan throat singing is
http://www.atech.org/khoomei/khoomei.html hosted by Steve Sklar. He even gives samples of many different throat singing styles. The spectrogram page is the best of the bunch, in my opinion.
I am a voice and speech teacher, and I use the term ululate to mean something different than overtone singing - ululate to me means to use the back of the tongue to go up and down (often very quickly) to make a shrill sound. Often done at a very high pitch, along the lines of 'ah-yuh-yuh-yuh-yuh" etc.
However, I went to the website above and listened to some of the samples of the overtone singing, and the harmonics do appear to be, in some cases, much like a ululation. The way the sound shifts is
very different (essentially the
harmonic that is shifting is different). From my limited knowledge of overtone singing, the formant (or overtone) which is changing is the one that is controlled by the tongue curling back, or retroflecting, as in English vowels that are R-colored, as in "Err, bird, furry, worm" etc. in US speech.
Hope that helps,
enrique
