Overtone singing

Anne-Marie Hefele is an overtone-singing specialist. What she can do is produce two melodies at once, through a technique called diphonic singing: an alteration of vocal timbre that, to the ear, sounds doubled — as if a second note were sounding right alongside the main one.

The technique isn't new. It developed independently in Tuva, in the Russian Federation, and in Mongolia. A similar tradition exists in Sardinia too, in its polyphonic choral singing.

Yes, I know — you already do backflips trying to sing one vocal line decently, let alone two. "That's alien stuff!", you might say. And you'd have a point — but hear me out first.

What's actually happening when you sing

Your voice already contains harmonic frequencies inside it. Sing a C, and your voice produces the frequency of that base C and, at the same time, its harmonics too — the whole-number multiples of that C's frequency, mixed with noise (I touched on this already in The responsible bass player).

That whole set is what we call timbre. Every sound-producing instrument has its own: a guitar doesn't sound like a bass, a flute doesn't sound like a viola. And the voice is the strangest instrument of all, because you can reshape it on the fly — the position of the tongue, the lips, the jaw all change the sound coming out.

Controlling the resonances that form inside the vocal tract, by placing those parts with precision, is exactly what overtone singing is: it concentrates sound energy on one particular frequency and pulls it out above the rest. The result is that you hear two distinct sounds — the main voice and the overtone. Shift the pitch of either one and you get something close to polyphony, out of a single throat.

The notes aren't yours to pick

The notes you can actually produce this way are limited to the natural harmonic series, which follows a simple mathematical pattern: given a fundamental frequency f, the harmonic series is the sequence of its whole-number multiples (f × 1, f × 2, f × 3…).

Take C4, which resonates at 261.6 Hz:

1. 1st harmonic: 261.6 Hz × 1 = 261.6 Hz (C4)
2. 2nd harmonic: 261.6 Hz × 2 = 523.2 Hz (C5, an octave up)
3. 3rd harmonic: 784.8 Hz (G5, the fifth of the C major scale)
4. 4th harmonic: 1046.4 Hz (C6)
5. 5th harmonic: 1308 Hz (E6 at -13.69 cents — the third of C major, slightly flat)
6. 6th harmonic: 1569.6 Hz (G6, another fifth)
7. 7th harmonic: 1831.2 Hz (B♭6 at -31.17 cents — a distinctly flat major seventh)

And so on. Those are the only notes overtone singing can reach — there's no picking a different set. Physics decides before you do.

The late Demetrio Stratos — together with Roberto Laneri — was one of the technique's foremost performers and researchers, and you can hear exactly why in this same track.

The moral of the story

You don't need to be an alien for this. You do need a serious amount of study and practice.

Is it a useful technique, or one more skill flex for its own sake? That's a matter of taste. Personally, I'd learn it for one reason only: to speak in two voices at once. It would be a wonderful, terrifying way to end an uncomfortable conversation.

Next time you listen to what Lalah Hathaway pulls off in that performance, think about it.