Modifying vowels is a common technique employed by singers when singing as a group to maximise the blended quality of the sound. Whilst there is natural variation of vowels between speakers and singers, a conscious effort is made to match the quality of vowels between singers. The purpose of this PhD project is to ascertain the extent to which singers modify their vowel production when blending with another voice. The project will also address the perceptual parameters of vowel matching and the aesthetic ideal of matched vowels. The project will involve both Music Information Retrieval of live recordings, synthesis and listening tests.