The basic function of speech is communication. The two main players in the act of communication are the source from whom the flow of information begins and the recipient of the information. The source constitutes the first phase of communication, while the recipient constitutes the second phase. In the case of speech or oral communication, the source of information is the speaker and the hearer or the listener is the recipient. They are also known as the addresser and the addressee, respectively.

The speaker uses a system to encode what he wants to communicate. Encoding is a mental and psychological process. Cerebral commands are sent to the vocal organs which are involved in the transmission of speech (Figure 1). These organs, in their turn, transmit speech in the form of sound waves through the air.

After the message has been encoded and transmitted, it has to be received and decoded by the listener. The listener receives the message and then decodes it, as shown in Figure 2. The audio signals are received via the auditory system, i.e. the ear, and the impulses are sent to the brain, where the content of the message is decoded. This is how communication takes place between the speaker and the listener, provided they share the common code (i.e. language).

The scientific study of the way speech sounds are produced by our vocal organs, the way they are perceived by the listeners and the way different sounds are combined into syllables, words and sentences is known as phonetics.