The following description is of the transcription scheme devised by Marvin J. Brown for AUA. It, or close variants of it, are used by leading language schools and universities throughout the world. It's also the basis for this site's transcription (referred to for short as IPA, rather than saying "an IPA-influenced transcription scheme".
Transcription is covered in the following sections:
(A guide to pronunciation of the transcription is available at Pronunciation Guide.)
Initial consonant clusters are transcribed using the symbols for the individual consonants, e.g. กลับ klàp, ควัน khwan.
Consonants which are not pronounced are not transcribed, e.g. จริง ciŋ, กษัตริย์ kaˑsàt.
Long vowels are transcribed with a doubled character, short vowels with a single one.
The following table refers to vowels as being in "open" or "closed" syllables. An open syllable is one that is written without a written consonant ; a closed one ends with a written consonant.
In the table "—" is used to represent an initial consonant or consonant cluster, and "–" to represent a final consonant.
When the first consonant is อ, อ is pronounced and transcribed as a glottal stop ʔ, e.g. ออก ʔɔ̀ɔk or อีก ʔìik.
For open short vowels, the glottal stop may (or perhaps “should”) be omitted in unstressed syllables to reflect normal pronunciation, rather than the “theoretical” pronunciation only used in extremely formal speech and dictation (the tone will also become mid-tone). E.g. สะพาน saˑphaan, rather than sàʔˑphaan.
The same applies to unwritten a in polysyllabic words, e.g. ทหาร thaˑhǎan, rather than tháʔˑhǎan.
Diphthongs are transcribed with two vowel symbols.
Note that AUA transcription does not handle short diphthongs, so เ—าะ, เ—ียะ and —ัวะ are transcribed as if normal length, i.e. aw ia and ua. The number of words containing short diphthongs is vanishingly small. The only reasonably common one is เปาะเปี๊ยะ (spring roll). Words containing short diphthongs are generally borrowed from Teochew or are onomatopoeias.
Tones are indicated by a mark above the first vowel in a syllable. The marks are:
Absence of a mark indicates mid tone.
Some examples: บาง baaŋ, ทัก thák, บาท bàat, หา hǎa, บ้า bâa.
Generally, AUA transcription does not include a syllable separator. This can lead to ambiguity. For example, the transcription for ฝึกหัด is fʉ̀khàt which is ambiguous. Is it fʉ̀kˑhàt, or fʉ̀ˑkhàt? It also doesn’t indicate stress. (Some suggest that stress is so regular that it doesn’t need to be explicitly shown.) Some sources (e.g. the Thai Dictionary Project (TDP) modify the transcription in two ways: (1) Represent the “h” in aspirated consonants with a superscript, e.g. พริก ˈpʰrík, and (2) separate syllable indicating stress using ˈ which is a vertical line, specifically acting as the primary stress marker in the International Phonetic Alphabet (IPA), e.g. ขัง ˈkʰǎŋ. ฝึกหัด is transcribed as fʉ̀kˈhàt. TDP transcribes โรงพยาบาล as ˈrooŋ pʰa.yaaˈbaan — rooŋ is treated as an isolated word, separated by a space from pʰa.yaaˈbaan where the two unstressed syllables are separated by a full stop or period.
Union method materials represents r as ʀ –
presumably to remind students that the consonant is pronounced
as "l" is rolled or trilled – at least in formal speech.
Some sources use a macron to indicate mid tone, e.g. บาน bāan.