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Ok, my mother tongue is Vietnamese and I often got difficulty making the English /t/ sound.

Here is what I discovered.

-If a /t/ is the beginning of word (Ex: /taɪ/ tie, /tɪn/ tin, /ˈtaɪ.lænd/ Thailand) or after a vowel (Ex: /prəˈtekt/ protect, /ˈæd.vɝː.taɪz.mənt/ advertisement), then when making the /t/, we need to release a lot of air from our throat through our mouth. In this case, /t/ is closer to Vietnamese /th/.

See some example:

http://dictionary.cambridge.org/dictionary/english/tie http://dictionary.cambridge.org/dictionary/english/tin http://dictionary.cambridge.org/dictionary/english/thailand?q=Thailand http://dictionary.cambridge.org/dictionary/english/advertisement http://dictionary.cambridge.org/dictionary/english/protect

-However, if /t/is after a consonant (ex: /ˈnaɪn.ti/ ninety, /ˈɪn.trəs.tɪd/ interested), then when making the /t/, we release just a little bit air from our throat through our mouth. In this case, /t/ is closer to Vietnamese /t/.

See some example:

http://dictionary.cambridge.org/dictionary/english/ninety http://dictionary.cambridge.org/dictionary/english/interested

To make it easier for you to compare, see the word /en.təˈteɪn/ entertain. The /t/ in /tə/ is after /n/, so it sounds like Vietnamese /t/ and /t/ in /teɪn/ is after /ə/ so it sounds like Vietnamese /th/

http://dictionary.cambridge.org/dictionary/english/entertain

I do not think stressed or unstressed syllable makes the difference. Ex, /t/ in /ˈæd.vɝː.taɪz.mənt/ advertisement sounds like Vietnamese /th/

So, Why does /t/ after a consonant produce less air than /t/ at the beginning of word or after a vowel?

  • @sumelic, the links can answer 30% of my question but not really all factors I mentioned in my question – Tom Aug 21 '15 at 2:16
  • OK, can you maybe edit your question to clarify which 70% of it is still unanswered? Just to give some background, the sound like Vietnamese "th" is called an "aspirated stop" or "aspirated plosive" and is transcribed as /tʰ/ in the International Phonetic Alphabet, while the sound like Vietnamese /t/ is called an "unaspirated stop/plosive" and is transcribed with a single /t/ in the IPA. Is your question about how to tell if a word spelled with "t" has an aspirated or an unaspirated stop? If so, the following might be of use: phonetic-blog.blogspot.com/2009/04/vot-is-more.html – sumelic Aug 21 '15 at 3:30
  • so what does "at the beginning of a syllable" mean? so /t/ is at the beginning of a syllable /taɪz/ in /ˈæd.vɝː.taɪz.mənt/, right? Not necessary at the beginning of the word as /taɪ/ in /ˈtaɪ.lænd/ ? – Tom Aug 21 '15 at 4:17
  • Yes, I want to know the difference between unaspirated /t/ & aspirated /t/. Can you write your answer? Thank you – Tom Aug 21 '15 at 4:24
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The distinction between these two sounds, both generally represented by the letter "t" in English, is actually also made for "p" and "k." Each of these sounds is transcribed /t/ /p/ /k/ in "broad" phonetic transcriptions, but in a "narrow," more detailed transcription, there are two main types that are recognized by phoneticians.

We call one type "aspirated," and in transcriptions that distinguish the two, it's represented by the letter with a superscript "h" after it: [tʰ] [pʰ] [kʰ]. (The sound /tʰ/ exists in Vietnamese, where it is written "th"; the other two sounds do not.)

The second type is called "unaspirated": it's represented by plain [t] [p] [k]. These should correspond approximately to the Vietnamese sounds written with the letters "t," "p," and "k."

When to use one or the other is explained as follows on John Wells's phonetics blog:

English [p t k] are aspirated

  • when they occur at the beginning of a syllable in which the vowel is strong.

They are unaspirated

  • when preceded by s at the beginning of a syllable
  • when followed by any FRICATIVE, as in lapse læps, depth depθ
  • if immediately followed by another plosive as with the k in doctor ˈdɒktə || ˈdɑːktər. The release stage of the first plosive is then usually inaudible (‘masked’).

I'd add to this that it's safe to aspirate any "t," "p," or "k" at the very start of a word, no matter what sound comes after it.

The above rules apply to pretty much all varieties of English. As you can see, using these rules requires a fair amount of knowledge of the sound patterns of English: you'll need to know how a particular word is divided in syllables.

When /t/ comes after a vowel or after "r" and before a "weak" vowel like [ə] (writer) or [ɪ] (writing), or before a completely unstressed [oʊ] (grotto) or [i] (jetty), there may be differences in American and British pronunciation.

Many American varieties of English have a third pronunciation of "t" which is written in the International Phonetic Alphabet as [ɾ]. A "d" in this position is usually pronounced the same way, so this is less commonly transcribed as [d] by some people.

The pronunciation of "t" as [ɾ] usually does not occur before a strong vowel sound (any other vowel than [ə] or [ɪ]), as described in the following question: Why do photons and protons exhibit such anomalous behavior?

  • 1
    Surely that /ɾ/ should be written [ɾ]. – tchrist Aug 21 '15 at 11:32
  • @Sumelic, what about the slightly aspirated T. Ex, in /en.təˈteɪn/ entertain, t in /tə/ is after /n/ & it sounds like slightly aspirated T – Tom Aug 22 '15 at 0:05
  • @Sumelic, I think slightly aspirated T close to Vietnamese "/t/*, while unaspirated T almost has no sound – Tom Aug 22 '15 at 0:22
  • A reduced pronunciation of /t/ (corresponding to your ‘third’ pronunciation) exists in all varieties of English as well, as far as I know—its exact manifestation just varies. AmE, SAE, and AusE/NZE will usually have [ɾ], IrE frequently [ɾ], [ʔ], [h], or [ɹ̝̊], different dialects of BrE either [ɾ], [t], or [ʔ], etc. (And you could add in a bit about the special circumstances around /nt/, as well as how strong vs. weak vowels are distributed.) – Janus Bahs Jacquet Aug 22 '15 at 15:00
  • Nice answer - but why's there no aspiration in ninety? – Araucaria Aug 22 '15 at 15:00
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Short answer

In General American English, a /t/ will tend to be voiced when it occurs after a nasal and before a weak vowel. This sounds a bit like a /d/ to many listeners. If you're looking at an IPA transcription in a good dictionary, such as Cambridge Dictionaries Online you should see that the /t/ has a little diacritic underneath. The symbol will look like this: . Voiced /t/s have no aspiration as is explained further below.

Detailed answer

It is a well known fact that /t/ is liable to be a voiced tap when it occurs after a vowel and before another weak vowel. So for example the /t/ in water will be pronounced [ɾ] in Gen Am. The Cambridge Dictionaries Online transcription for this is /ˈwɑː.t̬ɚ/. That little downwards arrow there, which should be directly underneath the 't', shows that this /t/ is likely to be voiced.

However, what's less well-known is that /t/ is also likely to be realised as voiced when it occurs between certain voiced consonants and a weak vowel. So for example /t/ may also be voiced when it occurs after /r, l, m, n, ŋ/ and before a weak vowel. So we will probably hear a tap or other voiced allophone in the following words:

If you look at the transcriptions for those words in the links you will see the voiced-t symbol, /t̬/. You can also hear a tap in most of the American English pronunciations there too.

OK, but why is there no aspiration there?

The English plosives /p, k, t/ usually occur with some aspiration before vowels (when articulated as plosives, not taps or glottal stops). This may be light or it may be strong depending on it's position in the word. These plosives are usually strongly aspirated when occurring word initially, at the beginning of a stressed syllable or when occurring before a strong vowel. Elsewhere, when occurring before a vowel, /t/ will be lightly aspirated. The exception to this is when the /t/ is preceded by an /s/. When this occurs the /t/ will be completely unaspirated, and will sound like a /d/ to many listeners.

Now this is what actually happens when we get an aspirated consonant in English. The plosives /p, k, t/ are typically voiceless. We make them by forming a complete blockage in the vocal tract which prevents the air from leaving the mouth. Behind this blockage there is a huge build up of air pressure as air is forced up from the lungs. This is called the hold phase of the consonant and with voiceless consonants it is accompanied by silence. This is because there is no air moving out of the mouth and the vocal folds (or vocal chords) are not vibrating. When we finally release the air we get an effect called plosion, caused by the air exploding out of the mouth.

Now usually these consonants occur before a voiced sound, most often a vowel. Vowels of course are voiced and this is what gives them pitch. So when we make a vowel we vibrate our vocal folds. However our vocal folds are generally a bit lazy when we speak English. They tend to kick in quite late and they often finish early too at the end of a word or syllable. When we get a vowel after a voiceless plosive in English there is a small gap before the vocal folds actually start vibrating. This lag is called the voice onset time, or VOT, for short. So the VOT is basically a gap between the release of the plosive and the beginning of the voicing of the vowel.

Now when we release a /p, t/ or /k/ the air that we release is being forced out of the mouth by air coming from the lungs. During the VOT period, before the vocal folds start vibrating, we can hear the turbulence of the air as it leaves the mouth, because there is no vocal fold vibration to drown the noise out. This turbulence that we hear has an /h/-like quality, and it is this sound that we recognise as aspiration. So basically aspiration is just the air rushing out of the mouth before the vocal folds get to work.

You will have noticed that I said when they are articulated as plosives further above. When /t/ occurs intervocalically (between two vowels) or between /r, l, m, n, ŋ/ and a weak vowel, we see assimilation. This means that the /t/ takes on features from the sounds next to it. In particular, it becomes voiced. In practice this means that we don't stop vibrating the vocal folds for the /t/. They vibrate all the way through from the previous sound, right through the /t/ and continue vibrating for the following vowel. It is this aspect of the /t/ that makes it sound like a /d/ to many speakers in words like water. The upshot of this is that because there is no gap in the voicing between the consonant and the following vowel, there is no aspiration.

Conclusion

In short the Original Poster is completely correct. It is not that they can't hear the aspiration because the /t/ is only lightly aspirated in the words ninety or entertain. It's that there actually is no aspiration in the pronunciations given in the audios from the dictionary. They have used a voiced allophone, instead of [t] for these words. This is not a case of interference from the Original Poster's first language. It's a case of razor sharp ears!

It might be worth mentioning that in British English the use of [ɾ] for /t/ is much rarer. We tend to stick with [t] when American speakers would use [ɾ]. If you listen carefully to the [t]s in the British English versions of the words in the audio, you will be able to hear the light aspiration.


Addendum for phonetics junkies

It might be worth mentioning that when we get at /nt/ sequence followed by a weak vowel, in rapid informal speech, the whole /nt/ sequence might get replaced by a single nasalised tap. So for example, we might see [ˈtwɛ̃ɾ̃i] for the word twenty. This instance of coalescent assimilation will often be perceived as /t/-elision by listeners.

  • Hmm… the first part of this doesn’t seem phonetically accurate. The háček under the t in /t̬/ does not indicate that the consonant is a tap, but that it is voiced. Between vowels, this voiced /t̬/ does indeed usually become a tap [ɾ], but that is not the case after a nasal. A tap is defined as “produced with a single contraction of the muscles so that one articulator (such as the tongue) is thrown against another” (Wiki), and in the position after a nasal, the tongue is already touching the alveolar ridge and does not move: it’s just a plosive. – Janus Bahs Jacquet Aug 22 '15 at 15:07
  • (By “and does not move”, I mean of course that it doesn’t move before the consonant is released—upon release, it does move, naturally. But if it were to be an actual tap, the corona would have to first move away from the ridge and then be brought back into brief contact with it before it was moved away again upon release. The sequence [nɾ] is in fact quite difficult to make, and languages that have [ɾ] often do not have [nɾ], substituting instead something like [nr] or [nd].) – Janus Bahs Jacquet Aug 22 '15 at 15:11
  • @JanusBahsJacquet Of course in terms of striking the ridge you're correct there. What I'm unsure about now is whether there is any anticipatory assimilation on the part of the /n/ such that its not actually a proper nasal stop but something more like a nasalised aproximant. If so, I'm pretty certain it would still be considered a tap, although, of course it isn't a fully articulated flap. My reason for saying this is that if you see John Well's blog here he clearly states that American tapped /t/ can have a lateral release. ... – Araucaria Aug 22 '15 at 15:18
  • @JanusBahsJacquet ... So my guess is that if they're still considered taps when they have a lateral release, they're probably considered taps when they have a nasal approach. For us to consider them plosives, I suppose we would need some complete stricture to form a blockage. I'm not sure that's happening here. However, I'll ask John Wells on Monday! – Araucaria Aug 22 '15 at 15:20
  • @JanusBahsJacquet Although, I'm going to do a minor edit now, because obviously there is no strike in the case we're most interested in here ... Thanks for pointing all that out! :) – Araucaria Aug 22 '15 at 15:22

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