The /th/ sound is defined as the interdental voiceless fricative /θ/. It is hard for Cantonese learners to acquire the voiceless interdental fricatives /θ/ because of the influence of their L1 - Cantonese. There is a direct link between speech production and speech perception. The mispronunciation of the English voiceless interdental fricative /θ/ as the labio-dental voiceless fricative /f/ by Cantonese speakers may be due to the inaccurate speech perception and inability to notice the dissimilarity between these two similar sounds. /θ/ and /f/ are similar in terms of their acoustic features and inaccurate speech perception may be caused by “Equivalence classification” (Best, 1995) that Cantonese learners are unable to make discrimination between the two similar consonant sounds /f/ and /θ/. During speech perception, /θ/ may be perceived to be equivalent to the labio-dental fricative /f/ in the Cantonese sound inventory and Cantonese speakers may not be able to discern the phonetic differences between a pair of the English /θ/ and the Cantonese /f/ because “phonetically distinct sounds in the L2 (the English /θ/) is assimilated to a single category as the Cantonese /f/ ” (Chan, 2012). or “because the Cantonese phonology filters our features of the English voiceless dental fricative /θ/ which are important phonetically but not phonologically” (Sewell & Chan, 2010).
