Tuvan throat singer gets in an MRI

Speaking with Chris Smith, York University, Canada's Chandan Narayan explains how he persuaded a Tuvan throat singer to perform inside an MRI scanner, revealing how the vocal tract's in their performers can create two sounds at the same time...

Chandan - My name is Chandan Narayan. I am a associate professor of linguistics at York University in Toronto, Canada. What we're hearing is a Tuvan throat singer. He's performing a style of singing called Sigit, characterized by a really amazing phenomenon, I think. There is a deep low frequency rumble, which is followed by a very high frequency whistle-like tone. He seems to be able to control both of these sounds independently and it's unique to the Tuvan people, the Tuvan culture.

Chandan - So that's the whistle that you hear on top of this growling low-frequency pitch. He's doing something that we all do when we speak vowels or when we sing: we produce a set of organized frequencies from our mouth. Now those organized frequencies are called formants. About two or three of these determine what our vowel characteristic is. So if we're saying an ah, or an oo or an ee, he's doing the exact same thing, but he is merging two of these formants to produce what's called a super-formant or a focused state. That's the whistle that we hear. We don't hear this in a normal speech because those two formants are separate. So he's done something with his mouth that drives these two formants together to produce this tone, this whistle-like tone. And he makes further refinements with his tongue to shift the locus of this tone so as to produce a melody.

Chris - What was the outstanding question then?

Chandan - We didn't know what he was doing until we did this study. So the question initially was how are they doing it?

Chris - Presumably these people learn this from other people. They're not born with the innate ability to do it, they won't know exactly what they're doing to get it to sound right. They just respond to positive feedback both in themselves and from others. And that's how they know how to do it?

Chandan - Correct

Chris - But how did you then approach this to actually work out what they were doing?

Chandan - We started off with pretty high quality recordings that we made in a sound booth at the university. And then we followed that up with MRI imaging. We had a singer from this group that was touring in Canada. We were able to get them to come to the university and produce these sounds in the MRI scanner. And so we took those images and kind of reverse engineered a model of their throats and their mouths, computing cross-sectional areas of the throat. So if you think of the throat as a giant tube with pinches all throughout the tube, those, those particular pinches affect the nature of the resulting sound. And so the MRI gave us a good roadmap as to where those pinches might be occurring. And then we gave that data to Brad Story, who is an expert in vocal track modelling. And he was able to produce a model, a computational model of the vocal tract and predict the types of sounds that the Tuvans were producing based on the shape of their vocal tract.

Chris - Based on what you now know from these observations, if we return to that sound we heard at the beginning, can you now explain in terms of the anatomy, how they're doing each of those two different components?

Chandan - Yes. The singers raise the base of their tongue towards the uvula, which is in the back of the throat. And what that does is it produces a very focused bundle of energy at a specific frequency. Now that bundle of energy at that frequency is then shifted by making a constriction at the front of the mouth. So that energy is what we hear as a whistle. And that whistle's precise tune is controlled by making a constriction at the front of the mouth, near the teeth with the tip of the tongue. So there are two constrictions being made: one at the back of the mouth and one at the front of the mouth. The back constriction produces this whistle and the front constriction plays the melody of that whistle.

Chris - And is that because by constricting the front and the back, you actually are creating effectively a resonant chamber out of the mouth that's got two different sizes: one which is the vocal folds up to the back of the tongue, and then another one, which is the bit to the front of the mouth as well?

Chandan - Correct. So when you make a constriction anywhere along this tube, you're actually coupling two tubes, one tube behind the constriction and one tube in front of the construction. So in the case of the vocal tract there'll be a resonating chamber behind the base of the tongue, and a resonating chamber between the back of the tongue and the tip of the tongue , and a small resonating chamber between the tip of the tongue and the end of your lips. So they are multiple resonating chambers all acting together to produce this whistle.

Chris - And to what extent, given it's so dependent on the anatomy, being able to put your tongue into those positions, is this unique to these people? Could anyone do this or is it something that they have the right head and mouth and vocal tract shaped in order to do this most effectively?

Chandan - No, there's nothing special about the anatomy of the Tuvan singers. It's a learned phenomenon. I've tried, I failed, but others have been quite successful.

Chris - Will you give us a demo?

Chandan - I'm sorry. No, I haven't had enough coffee.

Chris - It takes coffee, does it? Most people say whiskey.

Chandan - Actually, you know, this group, we, we took them out for a lunch after we did the recording and they were quite adamant that they should never have cold water. You know in North America people are really into having water with ice. So I offered them some and they were taken aback. They said that cold water would ruin their vocal folds and they would never be able to make money again!