for /t/ in English, the rule is approximately
when the phoneme /t/ is the first sound of a stressed syllable, pronounce it as the allophone [tʰ]
that's why <top> is [tʰɑp], and <stop> is [stɑp]
because in <top> the /t/ sound is the first sound of a stressed syllable
in phonology, for instance, we form equivalence classes of sounds on the grounds of not phonetic similarity but rather contextual non-overlappingness. a kind of anti-similarity
one of the core criteria for two phonetic sounds to be equivalent in a language is if those two phonetic sounds have strictly non-overlapping distributions
the more overlap they have, the LESS equivalent they are. similarity = difference
ok, so some folx wanted to know more about this in linguistics/phonology, so here goes
when we study how the sounds of different languages work, we find that a language doesn't just have a set of sounds that are used in the language
we also find that those sounds relate to one another in various ways
for example, if we consider the <t> in the word <top> and in the word <stop>, we can determine acoustically (via the waveforms/spectrograms) and physically by feel, that these are different sounds
but you, as an english speaker, perceive them and treat them as the same sound
to see that they're different, place your hand in front of your mouth and say "top top top top top" then say "stop stop stop stop stop"
you should feel a stronger puff of air for "top" than "stop"
if you find that you puff air out when saying the <p> as well, say the words "tub" and "stub", to reduce the puff from the <p>
