The most common sound represented by the letter r in English is the voiced postalveolar approximant, pronounced a little more back and transcribed more precisely in IPA as ⟨ɹ̠⟩, but ⟨ɹ⟩ is often used for convenience in its place. For further ease of typesetting, English phonemic transcriptions might use the symbol ⟨r⟩ even though this symbol represents the alveolar trill in phonetic transcription.
The bunched or molar r sounds remarkably similar to the postalveolar approximant and can be described as a voiced labial pre-velar approximant with tongue-tip retraction. It can be transcribed in IPA as ⟨ψ⟩ or ⟨ɹ̈⟩.
Browman, C.P.; Goldstein, L. (1995), "Gestural syllable position in American English", in Bell-Berti, F.; Raphael, L.J. (eds.), Producing Speech: Contemporary Issues: for Katherine Safford Harris, New York: AIP, pp. 9–33
Cornyn, William (1944), Outline of Burmese Grammar, Supplement to Language, vol. 20 no. 4, Baltimore: Linguistic Society of America
Delattre, P.; Freeman, D.C. (1968), "A dialect study of American R's by x-ray motion picture", Linguistics, 44: 29–68
Engstrand, Olle (1999), "Swedish", Handbook of the International Phonetic Association, Cambridge University Press, pp. 140–142, ISBN9780521637510
Fougeron, C (1999), "Prosodically conditioned articulatory variation: A Review", UCLA Working Papers in Phonetics, 97, pp. 1–73
Grønnum, Nina (2003), "Why are the Danes so hard to understand?", in Jacobsen, Henrik Galberg; Bleses, Dorthe; Madsen, Thomas O.; Thomsen, Pia (eds.), Take Danish - for instance: linguistic studies in honour of Hans Basbøll, presented on the occasion of his 60th birthday, Odense: Syddansk Universitetsforlag, pp. 119–130
Hallé, Pierre A.; Best, Catherine T.; Levitt, Andrea (1999), "Phonetic vs. phonological influences on French listeners' perception of American English approximants", Journal of Phonetics, 27 (3): 281–306, doi:10.1006/jpho.1999.0097
Ikekeonwu, Clara I. (1999), "Igbo", Handbook of the International Phonetic Association, Cambridge University Press, pp. 108–110, ISBN9780521637510
Moosmüller, Sylvia; Schmid, Carolin; Brandstätter, Julia (2015), "Standard Austrian German", Journal of the International Phonetic Association, 45 (3): 339–348, doi:10.1017/S0025100315000055
Puech, Gilbert (2013), "Prime constituents of Maltese sounds", in Borg, Albert; Caruana, Sandro; Vella, Alexandra (eds.), Perspectives on Maltese Linguistics, Berlin: Akademie Verlag GmbH, pp. 61–88, ISBN978-3-05-006275-4
Recasens, Daniel (2004), "The effect of syllable position on consonant reduction (evidence from Catalan consonant clusters)", Journal of Phonetics, 32 (3): 435–453, doi:10.1016/j.wocn.2004.02.001