The value of the stress mark after a vowel determines that vowelΓÇÖs intonation.
Intonation is the pitch contour of a sentence. All human speech rises and falls in pitch, and though you may not be aware of it, a lot of the meaning and structure of your speech is communicated by intonation. The value of the stress mark after a vowel indicates that vowelΓÇÖs potential for a pitch accent. I say ΓÇ£potentialΓÇ¥ because the actual pitch accent will depend upon the accents of the syllables around it; it will depend upon the pitch contour of the whole sentence, as a matter of fact.
To quote from AppleΓÇÖs Macintalk documentation: ΓÇ£A sentenceΓÇÖs basic contour is comprised of a quickly declining pattern with rises and falls around each stressed syllable in the sentence, followed by a slowly declining tone throughout the sentence, and finally a quick fall to a low pitch on the last syllable. The presence of additional stressed syllables causes the pitch to break its slow, declining pattern with rises and falls around each stressed syllable. Macintalk uses a very sophisticated procedure to generate natural pitch contours based on your marking the stressed syllables.ΓÇ¥
