Thai pronunciation problems : Voicing vs devoicing

Thai learners, like many others, have no grasp of the concept of voicing and de-voicing the English consonants, so /v/ is turned into /f/, /g/ to /k/, /d/ to /t/, /z/ to /s/ and /b/ to /p/.

In some cases, the opposite is also true, where for example /t/

becomes /d/ and /θ/ becomes /ð/. This essentially depends on the vowels preceding or succeeding the consonants.