Quote Originally Posted by zxc View Post
For instance, try saying these English words:
kit
pot
tap

Say them while holding your hand in front of your mouth to feel the air that comes out. When pronouncing the letters t,k,p, you'll feel a puff of air come out. It's called aspiration...
(These consonants are usually only aspirated at the beginning of a word ^or at the beginning of a stressed syllable.
ATTENTION! ATTENTION! The second "t" in "attention" is strongly aspirated -- as is the "t" in "atomic," and the first "t" in "potato".

However, the first "t" in "attention" is essentially silent, because in English we normally don't pronounce "doubled consonants" as two separate sounds; and the third "t" in the suffix "-tion" is, of course, pronounced like "sh". The second "t" in "potato" is not strongly aspirated, and is often a bit "voiced", so that the last syllable "-to" sounds more like "dough".

Also, contrast "atom" with "atomic" -- in the first word, the "t" is rather unaspirated, and often voiced, so that the word is almost a homophone of "Adam." But in the second word -- thanks to the influence of the stressed vowel "o" -- the "t" is totally unvoiced, but usually rather aspirated, with a strong puff of air.

In general, this would also be true for the "p" and "k" sounds -- thus, the first "p" in the noun "apocalypse" is more strongly aspirated than in the adjectival form "apocalyptic", since the stress moves from the "o" to the "y". However, the "k sound" (or rather, the hard-c) in both words is rather unaspirated, since the syllable "-ca-" is unstressed. But in "vacation", the k-sound is more aspirated, because it comes before the stressed "a".