RILM: "Particular pronunciations or dialects are important factors in the creation and execution of vocal music. Such sounds can have a dramatic effect on the coloration and rhythmic profile of a piece of music; the recreation of such sounds is thus of great importance."
"Historical and Regional Pronunciations in Vocal Performance,"
Performance Practice Review:
2, Article 4.
Available at: http://scholarship.claremont.edu/ppr/vol9/iss2/4