Overview of the human speech mechanism

The complexity of speech sounds

Talking about speech is the same way as we talk about a similarly complete task. This explanation involved the co-ordination of the lips, tongue, vocal folds, breathing and so on. The signals which is receipt by our ears as successive sounds arises from skills that we learn over years of our lives, even as our bodies grow ang age. We are producing the simplest speech sounds by co-ordinating a large number of things. Phonetics study about such kind of unpicking the sounds of speech and working out how all the components work together, what they do and when.
Exactly, there is one problem we face. The interconnectivity of the parts : in a way, we need, to know something about everything all of the time. This explaination is giving you an overview of the speech mechanism. This explaination is introducing a lot of basic terminology of phonetics.

Breathing

Speech sounds are made by manipulating the way air moves out of (or sometimes into) the vocal tract. Universally accross languages sounds of speech are produced on an out-breath. This kind of airflow is called pulmonic(the movement of air is initiated by the lungs; the Latin word for lungs is ‘pulmo’) and egressive(because the air comes out of the vocal tract; e-, out, -gress-, move forward): all spoken languages have pulmonic egressive sounds.

When you say aah or mmm for example. You will notice that the air is going out, this is because sounds mmm [m:] is diacritic for long; needs an out-breath with areasonable amount of air in the lungs. Try to say ahh or mmm again, but this time do this while you are breathing. You will find that it is quite hard and you will probably get a more croaky voice quality. This is because the vocal tract works best for speech when breathing out, i.e on an egressive airflow.

The lungs are large spongy organ in the thoracic cavity (chest), connected to the outside world via the trachea, or the windpipe. They are surrounded at the front by ribs, and at the bottom by the diaphragm. The ribs are attached to one another by intercostal muscles. In breathing in, the diaphragm lower and the intercostal muscles make the rib cage move upwards and outwards. This increase the size of the thoracic cavity, and so it lowers the air pressure. As a result, airflows into the lungs and they expand and fill up with air. Once inhalation stops, the diaphragm and the intercostal muscles relax, and exert a gentle pressure on the lungs. Air is forced out of the lungs, generating a pulmonic egressive airflow.

The larynx and voicing

The larynx is a structure built of cartilage. Its main purpose is as kind of valve to stop thing things going down into the lungs. Locating our larynx is quite easily. People usually called it as the Adam’s Apple or voice box. It is often visible as a notch at the front of neck.
The vocal folds or the vocal cords is located in the larynx. When we breathe, they are kept wide apart, which allows air to pass freely accross the glottis, the space between the folds, but when you speak, this vocal folds play an important role because they can be made to vibrate. This vibration is called voicing, so every sounds which are accompanied by voicing is called voiced sound, while those which are not are called voiceless sounds.

Simple experiment as an example. Try to say [m] but put your hands over your ears, you will hear a quite loud buzzing which is conducted through your bones to your ear. Try the same thing again but this time say a [s] sound, you will notice that the buzzing stops. Instead, you will here a hissing sound, which is due to the turbulent airflow near the back of the teeth.

Airflow

Air passes out of the vocal tract through the mouth or the nose. The way that it comes out affects the sound generated, so we need a framework to describe this aspect of speech.
Central airflow and Lateral airflow
Central airflow is when the air flows down the middle of the vocal tract, while the Lateral airflow is when the air flows down one or both sides of the vocal tract. In the theory, lateral airflow can also be produced at the lips.

Oral and nassal airflow
Air can exit the vocal tract through the nose or the mouth. This is controlled by the position of the velum. The velum is  a sort of valve that control airflow through the nose. This is the main item that control the nassal and oral airflow.

Oral airflow is produced when the nassal cavities are blocked blocked off when the velum is raised. In a simpler way, oral airflow is sounds with airflow exiting through the mouth. So on, if the velum is lowered, air flows through the nassal cavities, and out through the nostrils. If the air flows through the nose, it is called as nassal.

Place of articulation

Articulators are the parts of the oral tract that are used in producing speech sounds. They are divided into two groups, active and passive. Active articulators are ones that move: the tongue tip is an active articulators in sounds like [s t n], since it moves up to behind the teeth. Passive articulators are the ones that cannot move, but are the target for active articulators. In the case of sounds like [s t n], the passive articulator is the bony ridge behind the upper teeth,known as the alveolar ridge.

Bilabial
Bilabial sounds are sounds made at the lips. Bi means two, while labial is an adjective based on Latin word for lips.

Labiodental
Labiodental sounds are made with the upper teeth (dental) against the lower lower lip (labio). Logically speaking, labiodental sounds could involve the lower teeth and the upper lip, but this is difficult for most people to do: it involves protruding the jaw, and most people have upper teeththat sit in front of the lower teeth.

Labiodental sounds can be made with the teeth against either the inside surface of the lip (endolabial) or the outside edge of the lip (exolabial).

Dental
Sounds that involve an articulation made against the back of the upper teeth is called dental.

Alveolar
Alveolar sounds are made at the alveolar ridge. This is a bony ridge behind the upper teeth.

Postalveolar
Postalveolar sounds are made just behind the alveolar ridge. So, it is difficult to differenciate between alveolar and postalveolar sounds.

Retroflex
Retroflex sounds are made with the tongue curled (flex) back (retro) to the hard palate.

Coronal
In the phonology literature, sounds made with the front part of the tongue are often called as coronal.

Palatal
Sounds which are made by the tongue body, the massive part of the middle of the tongue, raised up to the hard palate or the roof of the mouth is called palatal.

Velar
Velar sounds are made with the tongue back (or dorsum) raised towards the soft palate.

Uvular
The uvula is the little fleshy appendage that hangs down in the middle of your mouth at the back. Sounds which are made in this uvula is called uvular.

Pharyngeal
The pharynx is the cavity behind the tongue root and just above the larynx. Pharyngeal sounds are made by constricting the muscles of the neck and contracting the pharynx; this kind of articulation occurs rarely in Englsh.

Glottal
Glottal sounds are made at the glottis, the space between the vocal folds, which are located at the 
larynx.

Manner of articulation

The way sound is made (rather than where it is made) is called manner of articulation.

Stop articulations
Stop articulations are those sounds where a complete closure is made in the oral tract between two articulators; this stop the air moving out of the oral tract.

Fricative articulations
Fricative articulations are the result of two articulators being in close approximation with each other.
Resonant articulations


If articulators are held so as not to generate friction, but to allow air to pass between them smoothly, then we get articulations known as resonant. The degree of stricture is known as open approximation, and consonant sounds generated this way are called approximation. Vowels are another kind of resonant articulation.   

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