The basic process of voice production is the same for both speaking and singing. The "brain" sends signals through the nervous system to the muscles of the head, neck, and torso in order to produce inhalation prior to voicing. At the end of inhalation, a number of actions take place: the motion of the arytenoid cartilages in the larynx brings the vocal folds close to each other; the volume of the lungs decreases to produce positive air pressure in the lungs; and air begins to flow toward the larynx. The resulting air pressure on the surface of the vocal folds moves them into the beginning of the first cycle of motion. After the vocal folds are moved a little, they will then move in the other direction primarily because of their elasticity and changing air pressures. If airflows and air pressures are maintained, the vocal folds will continue to oscillate out and in, creating phonation. If the vocal folds are vibrating out and in at 200 times per second, they are said to be vibrating at 200 Hz. When phonating at "concert A" of 440 Hz, the vocal folds cycle out and in 440 times per second. A soprano singing "high C" at 1024 Hz has her vocal folds vibrating at 1024 times per second.
The glottis is the space between the vocal folds. During each cycle the glottis has three distinct phases: opening, closing, and closed. Sound is created due to the changing airflow traveling up through the glottis (between the vocal folds) during each cycle of vibration.
Differences between the Voices of Women and Men
The voices of women and men differ relative to a number of aspects including larynx size, speaking pitch, pitch range, the space between the vocal folds, and the incidence of voice problems.
Before puberty, the average speaking pitch and size of the larynx are about the same for both males and females. The fundamental frequency of the voice (strongly related to the perception of pitch of the voice) is about 250 Hz and vocal fold length is about 10.4 mm just before puberty. Vocal fold length then increases by 3-5 mm in the female and 5-10 mm in the male during puberty. This lengthening (and corresponding mass increase) reduces normal average speaking pitches to about 120 Hz in the male and 200 Hz in the female. The singing voice is partly categorized by the range of fundamental frequencies the person can sing in performance, as well as by the quality, agility, and how big a sound the voice can produce.
The glottis includes both the space between the vocal folds, called the membranous glottis, and the space behind the vocal folds between the arytenoid cartilages, called the cartilaginous glottis. The female's larynx typically will appear to have a little more space between the arytenoids than the male's larynx does. This is thought to be primarily an anatomical difference and secondarily a cultural difference. This glottal shaping apparently helps to give the female voice a typically softer quality due to the corresponding airflow through the larynx.
The higher pitch (almost an octave) of women compared to men means that the vocal folds vibrate or come together almost twice as many times per second as those of the male. This greater number of vibrations may correspond to the finding that adult females tend to have a greater incidence of vocal nodules (small growths on both vocal folds opposite one another). That is, there may be a greater potential for tissue damage for women due to the larger number of times the vocal folds touch each other during phonation.
When we speak, we typically use what is called the "chest" or "modal" register. It comprises those pitches that are normal to the speaking range. If one phonates outside of the normal speech range, one encounters "vocal fry" at the low pitch end and "falsetto" at the high pitch end. Vocal fry, also called pulse register, sounds somewht like bacon frying. The vocal folds may be compressed together from the sides, but the vocal folds themselves are very slack. Falsetto often sounds high pitched, thin, and breathy. The cricothyroid muscles (located at the front of the larynx) stretch the vocal folds almost maximally. In falsetto, only the medial edges of the vocal folds are in motion, and the vocal folds may be partially separated.
The vocal pedagogy professions have discussed vocal registers for many years. There are various views about the number of vocal registers, from none, to one, to many. An often-discussed register of both the speaking and singing voice besides vocal fry, chest, and falsetto is the "head" voice. The head voice typically involves pitches in the high chest register and above. The head voice may have slightly less closeness of the vocal folds in the female voice and more vocal tract enlargement for the male voice. The "head voice" may be accompanied by a sensation of sound (heard or felt) in, around, or in front of the upper portion of the head. The sensations of head voice may be carried to the lower notes of male singers. Some pedagogues reserve head voice in female singers for relatively high pitches.
"Blending" the registers is important in both the speaking voice and the singing voice. In order to move smoothly up or down in pitch between the chest and head voice registers (or between any two adjacent registers), the registers must blend. If they don’t, abrupt changes in pitch and brief cessations of sound, called voice breaks, occur. Many techniques are used to blend the registers, and all must address (1) coordinating the muscles of the larynx to prevent voice breaks, and (2) maintaining the acoustic pressures in the airways to avoid undesirable quality changes.
Age and Changes in Voice
The larynx is composed of tissues similar to the rest of the body, and it probably ages in a similar manner. The vocal folds may atrophy, which may lead to vocal fold bowing and a weaker voice. The mucosal covering of the vocal folds may thin or thicken, with changes of elasticity. Laryngeal cartilages may harden by ossification or calcification, depending on the cartilage type. The joints of the larynx can degenerate and may move with less range of motion. Mucous glands of the larynx, important for applying a protective lubricating fluid on the vocal folds, may reduce function. Blood supply may change. Pitch, loudness, quality, and control all may be deleteriously affected by the aging processes. Research suggests that good general fitness appears to correspond to a relatively clear voice.
Any difference in the size, mass, stiffness, or shape of one vocal fold compared to the other may create conditions leading to irregular vocal fold vibrations and a rough sounding voice. These differences may be due to disease, injury, aging, or misuse of the vocal folds. For example, a growth such as a large polyp or large nodule can correspond to uneven, irregular, or asymmetric vocal fold motion and a rough voice quality. In these cases, the vocal folds do not vibrate the same in the next cycle as in the current cycle. This creates different characteristics of the puff of air that comes through the larynx with each cycle. Since the sound is created by the puffs of air, the sound is different in each cycle. The ear picks this up, not as individual differences in sound from cycle to cycle, but as an overall change in the quality of the sound.
Some Basic Concepts about Voice Production
The quality of the sounds we hear is determined by the sound made at the larynx, the filtering of the sound by the vocal tract (the airway above the larynx), and the reception and processing of the sound by the ear and brain.
The pitch of the voice corresponds perceptually to the number of times per second the vocal folds come together during phonation. For example, a pitch corresponding to 250 Hz (near middle C on the piano) means that the vocal folds vibrate away from and then back toward each other 250 times per second (250 cycles per second).
The loudness of the voice depends on how close the vocal folds are to each other, how much air pressure there is below the larynx, the fundamental frequency of the voice, and the resonance structure of the vocal tract. Loudness of the voice will generally increase when the air pressure in the lungs increases.
Vocal problems may arise if the vocal folds are pressed too tightly together during phonation. This hyperadduction of the vocal folds may help cause or be related to overuse and fatigue of larynx muscles, and lead to adverse tissue reactions.
Hoarse or rough voice quality may arise when the two vocal folds are not alike or do not vibrate the same way, creating a different sound for each vocal fold vibration. This could be caused by swellings such as edema, polyps or nodules, or by paralysis and other neuromuscular problems.
Breathy voice quality implies that a relatively large amount of air is used during phonation. Some of the air is not modulated by the vibrating vocal folds, but comes through the glottis as turbulent flow converted to noise. Usually when there is breathy phonation, the glottis does not fully close during vocal fold vibration.
Aphonic production means that there is no phonation (no vibration of the vocal folds), as in voiceless whisper or severe laryngitis that prevents vocal fold vibration.
A diplophonic voice is one in which two simultaneous pitches are perceived.
Vocal fry is phonation at very low frequencies. Generally vocal fry sounds like a rapid series of taps. Overuse of loud vocal fry may be related to vocal problems.
High intelligibility of speech requires sufficient respiratory effort and appropriate laryngeal function; adequate loudness of consonants and vowels requires sufficient air pressures and airflows.
A formant or resonance of the vocal tract above the vocal folds is a frequency region that will strongly pass energy in that frequency region if it receives energy at those frequencies from the glottal source (glottal flow). The formant frequencies depend upon the size and shape of the vocal tract.
An important frequency region that "rings" typically independently of the sung vowel is the "singer's formant." This may be created when the area at the top of the larynx tube is small relative to the area of the pharynx just above the larynx tube. The larynx tube then "rings" at about 28,000 - 32,000 Hz. This phenomenon is more prevalent in male singers. This technique can also be used by nonsingers to create additional loudness and carrying power to the voice.
The larynx may be lowered to increase the length of the vocal tract. This action lowers the formant center frequencies and can make the sound "darker". In addition, this may also enhance the "singer's formant". Changes in the vocal tract configuration also can be used to create subtle changes in quality.