Properties of the duration of English rhythm segments

The properties of the duration of English rhythm segments, which comprised a set of stressed and unstressed syllables, were investigated. The speech sounds of short sentences, each including three to five stressed syllables, spoken by 20 native speakers were used. The following definitions of the rhythm segment were adopted for comparative judgment: a stressed syllable and succeeding weak syllable sequence; preceding weak syllable sequence and a stressed syllable; a stressed syllable and a half of preceding and succeeding weak syllable sequences; and the interval between adjacent stressed syllables. The measurement based on the detailed acoustical analysis showed that the duration of each segment by the native speakers was distributed around a peak at about 0.7 second, which was considered to be a target rhythmic period. Some segments, which include the secondary stressed syllables, were distributed separately around a half of the target period. However, they could not be put closer to the main distribution, by exchanging the secondary stressed syllable for the primary one or weak syllable. For the universal description of the rhythm structure, the duration of the rhythm segment was approximated by a series of the target periods into which a half period was interpolated irregularly.