How the Singing Voice is Produced

HOW PHONATION OCCURS

• The abdominal muscles and respiratory system increase breath pressure in the lungs.
• Airflow rises through the trachea to the vocal folds.
• Vocal fold vibration is initiated in response to airflow. The folds open and close rapidly, first resisting the air, causing air pressure to increase below the folds, then bursting open, then closing again, from the bottom of the folds upwards. This is called aerodynamic myo-elastic oscillation.
• Aerodynamic energy is converted to acoustic energy or partials. Partials that are integer multiples of the fundamental frequency are called harmonics.
• Certain harmonics can be boosted or amplified by their proximity to a formant, a pocket of air in the vocal tract that vibrates at different pitches or frequencies depending on the size and shape of the container (mouth or pharynx).

Resonance in singing is basically how formants and harmonics interact in the vocal tract.

There are two cavities in the vocal tract that function as resonators:

1. The pharynx (also called the throat) comprised of the laryngopharynx, the oropharynx, and the nasopharynx.

2. The mouth, (which includes the tongue, soft palate, and lips).

Other areas of the body, such as the nasal and chest cavities, vibrate in response to resonance occurring in the pharynx and mouth; these are examples of sympathetic resonance.

HARMONICS

Harmonics are heard by the human ear as part of the spectrum of sound occurring along with the basic pitch. They provide the richness and timbre or tone quality of a musical sound, whether that sound is a voice or an instrument.

Every sound in nature has harmonics. Only a computer, synthesizer, or tuning fork can generate a sine wave, devoid of harmonics.

When the vocal folds open and close in the vibratory cycle, they convert aerodynamic energy, or air, to acoustic energy, or partials, including the fundamental (basic pitch) and other overtones.  

Frequencies are represented in Hertz (Hz) or cycles per second.

The partial known as the fundamental frequency (F₀) is determined by the number of times the vocal folds open and close every second. F₀ is also known as the first harmonic or H₁.

Harmonics are partials that occur at whole integer intervals above the frequency of the fundamental.

For example, if the fundamental, F₀, or H₁ (the pitch) is 220, the next harmonic would occur at 440 (220 x 2), the next at 660 (220 x 3), the next at 880 (220 x 4), etc. When you change pitch, you also change the frequency of each of the higher harmonics that are generated along with the fundamental frequency F₀-H₁.

Harmonics are generated by the vibrating vocal folds.  As the folds lengthen or shorten, pitch changes. Each new pitch generates a new harmonic series above it.  Faster vocal fold vibrations (higher pitches) generate higher harmonics.

A firmer closure of the glottis at the onset of sound produces stronger harmonics. On lower pitches, with firm glottal closure, the harmonics are strong and close together.

On higher pitches, the harmonics are spread further apart because they are multiples of the fundamental frequency. The higher that number gets, the further apart those multiples will be.

Harmonics are fixed- their frequency can’t be altered, but they can be boosted in strength or power by being in proximity to the frequency of a formant. We cannot change the generated harmonic frequencies, but we can to some degree alter formants by changing the shape of a resonator (the mouth or pharynx).

Without the assistance of the vocal tract, the fundamental pitch, F₀, would be the loudest, and the higher harmonics would sequentially decrease in loudness. Each next higher harmonic would be softer than the preceding one. (That’s called a “roll-off”). The decibel level of the harmonics decreases at about 12 dB for each successive harmonic.

However, the vocal tract acts as a filter where partials are either boosted or attenuated (damped) depending on the size and shape of the containers of the mouth and pharynx. The vocal tract is where the soft buzz-like quality, as the sound manifests at the vibrating vocal folds, is transformed.

The vocal tract can assume different shapes, altering formant frequencies. Harmonics in the frequency vicinity of a formant are boosted. The relative strength of certain harmonics gives a musical sound its characteristic timbre or tone color.

CHANGING HARMONIC FREQUENCIES

Harmonics are generated at fixed intervals above pitch. The harmonic frequencies change whenever the fundamental or pitch changes.

When you sing the same vowel on successively higher pitches the harmonics rise with the pitch.

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