A stress-timed language, such as English, is one in which the
time intervals between stressed syllables in an utterance are
relatively equal. This differs from a syllable-timed
language, such as Spanish, in which all of the syllables in an
utterance tend to have the same length.
For English, this means that word stress within a sentence can be produced partially by assigning a metre to the speech. The ability to understand the speech depends directly on how well the metre is assigned.
The following are recordings of the same sentence produced with different degrees of prosody:
The rhythm in utterances 2 and 3 was produced with Cyng.
Here are some preliminary experiments with automatic duration assignment.