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Deterding, David (1997). "The formants of monophthong vowels in Standard Southern British English Pronunciation". Journal of the International Phonetic Association. 27 (1–2): 47–55. doi:10.1017/S0025100300005417. S2CID146157247.
Hawkins, Sarah and Jonathan Midgley (2005). "Formant frequencies of RP monophthongs in four age groups of speakers". Journal of the International Phonetic Association. 35 (2): 183–199. doi:10.1017/S0025100305002124. S2CID53532910.