 Canadian raising

Canadian raising names a pronunciation pattern in which the starting portion of the diphthongs conventionally transcribed /aɪ/ and /aʊ/ is raised in particular contexts, especially before a voiceless syllable coda. The pattern is associated with Canadian English, while related effects also occur in other North American varieties.^[ref]

Comparing lout and loud in controlled contexts can illustrate a voiceless-versus-voiced following consonant, but an acoustic test should compare repeated tokens and their formant trajectories. Sky Onosson's dissertation separates changes in trajectory from the shortening of vowels before voiceless consonants; its abstract reports different cross-dialect patterns for the two diphthongs. A single midpoint or duration can therefore miss part of the phenomenon. Raising refers to vowel quality, not simply to a higher voice fundamental frequency.