Here is a detailed explanation of the acoustic phenomenon where certain elite Mongolian throat singers can produce three simultaneous pitches.
Introduction: Beyond the Dual Tone
Most people familiar with Tuvan or Mongolian throat singing (Khoomei) understand it as a "biphonic" art form. The singer produces a fundamental bass note (the drone) and simultaneously isolates a high-pitched whistle-like melody (the overtone) above it.
However, advanced acoustic research and ethnomusicological study have revealed a rarer, more complex phenomenon: Triphonic Singing. In this state, a virtuoso singer manipulates their vocal tract to produce the fundamental drone, the high whistle overtone, and a third, distinct mid-range pitch, effectively singing a three-note chord solo.
This capability relies on extreme control over the larynx, the ventricular folds (false vocal cords), and the resonant chambers of the vocal tract.
1. The Acoustic Foundation: How Overtone Singing Works
To understand the third pitch, one must first understand the first two.
- The Source (The Fundamental): Every sound we make is composite. When a singer phonates, their vocal folds vibrate at a specific frequency (e.g., 100 Hz). This is the pitch our brain identifies as the "note."
- The Harmonics (The Overtones): Alongside that 100 Hz note, the vocal folds also produce integer multiples of that frequency (200 Hz, 300 Hz, 400 Hz, etc.) called harmonics. Usually, these are blended into the "timbre" or color of the voice.
- The Filter (The Vocal Tract): By changing the shape of the mouth, tongue, and throat, a singer creates "formants"—resonant chambers that amplify specific harmonics while dampening others. In standard Khoomei, the singer amplifies one high harmonic so loudly that it is heard as a separate whistle.
2. The Mechanics of the Third Pitch
The production of a third pitch requires a radical reconfiguration of the throat's anatomy, specifically involving the Ventricular Folds.
A. The False Vocal Cords
Located just above the true vocal cords are the vestibular folds, commonly known as "false vocal cords." In normal speech or Western singing, these remain open and passive. In styles like Kargyraa (the deep, growling style of throat singing), the singer constricts the throat to bring these false cords together.
B. Period Doubling (The Sub-Harmonic)
When the false vocal cords vibrate alongside the true vocal cords, they typically vibrate at half the speed of the true cords. * If the true cords are vibrating at 100 Hz... * The false cords vibrate at 50 Hz.
This creates a "sub-harmonic" or an undertone an octave below the fundamental note. This creates the rich, buzzing texture associated with Kargyraa.
The Triphonic Breakthrough: In the rare instances where three pitches are detected, the singer is managing a delicate balancing act: 1. Pitch 1 (Low): The sub-harmonic growl generated by the false vocal cords. 2. Pitch 2 (Mid): The fundamental frequency generated by the true vocal cords. 3. Pitch 3 (High): A high-frequency harmonic isolated by the tongue and lips.
3. Laryngeal Positioning and "Double Resonance"
Producing these three sounds is not enough; they must be distinct to the ear. This is achieved through precise laryngeal positioning.
- Constriction: The singer constricts the aryepiglottic sphincter (a muscle ring at the top of the larynx). This creates a very narrow tube.
- Chamber Separation: By positioning the tongue (often curling it backward or pressing it to the roof of the mouth), the singer effectively divides the vocal tract into two distinct resonant chambers: one behind the constriction (the pharynx) and one in front (the mouth).
This "double resonance" allows the singer to tune the cavities independently. The back cavity reinforces the low and mid frequencies (the drone), while the front cavity acts as a precise filter to isolate the high melody.
4. Why Is It So Rare?
Hearing three distinct pitches is psychoacoustically difficult for the listener and physically grueling for the singer.
- Masking: The human brain naturally wants to blend the mid-range fundamental and the low sub-harmonic into a single, buzzy sound. It takes a specific ratio of volume (amplitude) between the three frequencies for the ear to separate them.
- Physical Tension: Engaging the false vocal cords while maintaining the fine motor control of the tongue required to isolate the high harmonic requires conflicting muscle tensions—tightness in the throat but dexterity in the mouth.
- The "Beat" Phenomenon: Often, the interaction between the true and false folds creates "beating" or amplitude modulation rather than a clear third pitch. Only the most skilled singers (such as those from the Huun-Huur-Tu ensemble or master soloists) can stabilize the vibration enough to make the third pitch discernable.
Summary
The discovery of triphonic singing fundamentally changed our understanding of the human voice's limits. It proves that the vocal tract can function not just as a single instrument, but as an entire ensemble. By utilizing the true vocal cords, the false vocal cords, and dual-chamber resonance simultaneously, a Mongolian throat singer becomes a living synthesizer, generating a bass line, a rhythm guitar (the mid-range fundamental), and a lead melody all at once.