Lee-Kim, Sang-Im (December 2014). "Revisiting Mandarin 'apical vowels': An articulatory and acoustic study". Journal of the International Phonetic Association. 44 (3): 261–282. doi:10.1017/S0025100314000267. S2CID16432272.
Bailey, Charles-James N. (1976). "Some additions to the phonetic alphabet". Journal of the International Phonetic Association. 6 (1): 32–34. doi:10.1017/s002510030000147x. JSTOR44525830.
Bailey, Charles-James N. (1976). "Some additions to the phonetic alphabet". Journal of the International Phonetic Association. 6 (1): 32–34. doi:10.1017/s002510030000147x. JSTOR44525830.
Lee-Kim, Sang-Im (December 2014). "Revisiting Mandarin 'apical vowels': An articulatory and acoustic study". Journal of the International Phonetic Association. 44 (3): 261–282. doi:10.1017/S0025100314000267. S2CID16432272.