IWell, it’s about something I’ve always heard from my teachers, they always say one feature of American English is the merger of t’s and d’s between vowels and that they are pronounced like d’s. And, even though I’m aware of this, I’ve made a mistake in my English class because, in my opinion, they are not pronounced exactly as a normal "d". I mean, my mistake was to single out the pronunciation of the "d" in the word “reading” as a characteristic of American English, and the teacher said it was pronounced as in any other dialect and that the typical feature is the "t" softened to "d", but the point is that I do think the “d” in “reading” or the “t” in “writing” are equal, but not pronounced exactly as the “d” in “day”. In fact, we Spaniards hear it quite like a Spanish soft “r”, but it could be just a confusion we have. I don't know if I was too clear...
What do you think?
You're talking about a process called intervocalic alveolar flapping
, which though also present in other varieties is particularly widespread and prominent in American English. Indeed, the resulting sound is
identical to Spanish ere
, but most English-speakers don't realise this and perceive it as "d".
The Wikipedia article I linked to gives a pretty comprehensive overview of the phenomenon but one interesting detail it omits is that alveolar flaps are optionally deleted in informal speech. That is, reading
may come out not as ['ɹi:ɾɪŋ] but as ['ɹi:.ɪŋ]. (In rapid speech, vowels may coalesce, but my general perception is that they're kept distinct.)