How Does Our Voice Work?
Voice production is a complex interaction between airflow, vocal fold vibration and the acoustics of the vocal tract. Although these elements are often described separately to make the process easier to understand, in reality they function as a highly coordinated and interconnected system.
Airflow: the energy behind the voice
Voice begins with the respiratory system.
During exhalation, the lungs generate the airflow and pressure required for phonation. When the vocal folds are brought into an appropriate position for voicing, aerodynamic forces interact with the elastic properties of the vocal fold tissue, allowing self-sustained vibration to occur.
This means that breathing for singing is not simply about taking a large breath or pushing more air. What matters is the efficient coordination of airflow, pressure and laryngeal function according to the demands of the sound we want to produce.
Vocal fold vibration: from airflow to acoustic energy
The vocal folds are two layers of highly specialised tissue located inside the larynx.
During phonation, they rapidly open and close, interacting with the airflow coming from the lungs. Rather than thinking of the vocal folds as objects that simply “produce sound,” it is more accurate to understand their vibration as a process that modulates the glottal airflow.
A relatively steady flow of air from the respiratory system is transformed into a rapidly changing, pulsating airflow. This creates fluctuations in air pressure that propagate through the vocal tract as an acoustic wave.
The frequency at which the vocal folds repeat this vibratory cycle is closely related to the fundamental frequency (F₀) of the voice, which we perceive primarily as pitch.
The vocal tract: shaping the sound
The acoustic energy generated at the level of the larynx then interacts with the vocal tract, the system of air-filled spaces above the vocal folds, including the pharyngeal, oral and, when acoustically coupled, nasal cavities.
The vocal tract acts as an acoustic filter.
Its size and shape determine its resonant frequencies. As we move the tongue, jaw, lips, soft palate and other structures, we alter the geometry of the vocal tract and therefore its acoustic properties.
Some frequencies within the acoustic signal are enhanced, while others are attenuated. These resonances play an essential role in determining vowels, timbre and vocal quality.
This is why relatively small adjustments within the vocal tract can produce significant changes in the sound we hear, even when the behaviour of the vocal folds remains relatively similar.
But it is not simply “source + filter”
The traditional Source–Filter Theory provides an extremely useful framework for understanding voice production: vocal fold vibration creates a glottal source, while the vocal tract filters its acoustic spectrum.
However, the human voice is more interactive than this simplified model might suggest.
The vocal tract does not always behave as a passive filter operating independently of the vocal folds. Acoustic pressures within the vocal tract can interact with glottal airflow and, under certain conditions, can even influence vocal fold vibration itself.
This phenomenon is known as source–filter interaction or source–filter coupling and is particularly relevant to singing, where changes in pitch and vocal tract configuration can create strong interactions between harmonics of the voice and vocal tract resonances.
A more complete way of thinking about voice production is therefore not as a simple chain of independent events, but as a dynamic system in which respiration, vocal fold vibration, airflow and vocal tract acoustics continuously interact.
Voice is not produced by one structure alone. It emerges from the coordinated interaction of airflow, vibrating tissue and acoustics.