Voiceless vowels

A common feature of conversational speech is the devoicing of vowels in unstressed syllables, especially adjacent to voiceless consonants. The IPA marks voiceless vowels with the diacritic .

The commonest environment for devoicing is where there is an unstressed vowel with voiceless consonants on either side. Words like ‘potato’ and ‘suppose’, which have unstressed first syllables and voiceless consonants on either side of the vowel, frequently have voiceless vowels in the first syllable: .

In a few cases, devoicing can give rise to pairs of words which are only slightly different such as: ‘sport/support’,  ; ‘please/police’,  . The main differences in these pairs are in the co-ordination of voicing with other articulatory events and the duration of the surrounding sounds. For example, in ‘sport’ vs. ‘support’, the main difference is in the immediate start of voicing on release of the plosive in ‘sport’, and the rounding starting earlier in ‘sport’ than in ‘support’. In the ‘please/police’ example, the main difference is in whether there is voicing coordinated with lateral airflow or not.