We can study stress from the point of view of production and perception; the two are obviously closely related, but are not identical.

 The production of stress is generally believed to depend on the speaker using more muscular energy than is used for stressed syllables. When we produce stressed syllables, the muscles that we use to expel air from the lungs are often more active, producing higher subglottal pressure.

 In terms of perception, all stressed syllables have one common characteristic; prominence.


 Stressed syllables are recognized as stressed because they are more prominent than unstressed syllables.

 Four different factors make a syllable prominent :
 Loudness : Stressed syllables are louder than unstressed ones; in other words, loudness is a component of prominence.

 Length : One syllable is made longer than the others.
If one syllable is made longer than the others, this syllable is heard as stressed.

 Pitch : Pitch is closely related to the frequency of vibration of the vocal folds and to the musical notion of low- and high- pitched ones. It is a perceptual characteristic of speech.
- The high-pitched syllable is stressed . On the contrary,
low-pitched syllables are unstressed.

 Quality : A syllable will tend to be prominent if it contains a vowel that is different in quality from neighbouring vowels.

Prominence, then, is produced by four main factors:
Loudness, length, pitch and quality.