Speech Production
The gross components of the speech system are the
lungs, trachea (windpipe), larynx (organ of speech production), pharyngeal
cavity (throat), oral or buccal cavity (mouth), and nasal cavity (nose).
In technical discussions, the pharyngeal and oral
cavities are usually grouped into one unit referred to as the vocal tract, and
the nasal cavity is often called the nasal tract. Accordingly, the vocal tract
begins at the larynx (vocal cords or glottis) and terminates at the input to
the lips. The nasal tract begins at the velumand ends at the nostrils. When the
velum (a trapdoor like mechanism at the back of the oral cavity) is lowered,
the nasal tract is acoustically coupled to the vocal tract to produce the nasal
sounds of speech.
Meanwhile, air enters the lungs via the normal
breathing mechanism. As air is expelled from the lungs through the trachea, the
tensed vocal cords within the larynx are caused to vibrate by the air flow. The
airflow is chopped into quasi periodic pulses, which later are modulated in
frequency in passing through the throat, the oral cavity, and possibly the
nasal cavity. Decoding on the positions of the various articulators (i.e., jaw,
tongue, velum, lips, and mouth), different sounds are produced.
In the physiological mechanism for creating speech,
the 11.mgs and the associated muscles act as the source of the air for exciting
the vocal mechanism. The mucle force pushes air out of the lungs and through
the trachea.
When the vocal cords
are tensed, the airflow causes them to vibrate, producing so called voiced
speech sounds. When the vocal cords are related, in order to produce a sound,
the airflow either mut pass through a constriction in the vocal tract and
thereby become turbulent, producing so called unvoiced sounds, or it can build
up pressure behind a point of the total closure within the vocal tract, and
when the closure is opened, the pressure is suddenly and abruptly release,
causing a brief transient sound.
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