Learning American Pronunciation: When T sounds more like D

In the middle of some words, the "t" sounds more like a light or short “d” sound.  This is because we say the "t" without a puff of air.  Produce t without letting the air out, or add a little voicing (think “d.”)

This is also sometimes referred to as the “flap” t.

Some examples:  better, batter, butter, letter, waiter, writer, water, litter, greater, lighter, wetter
        waited, righted, lighted, matted, sighted, fitted, metabolic
        artificial, comforting, dirty
        fatal, hospital, turtle

Listen to these words.  The first has the t pronounced with the puff of air, and the second is without, the way most Americans produce the word.

You can pronounce an aspirated t in these words and it will be correct.  Americans usually only use the aspirated t in these words if they are trying to be extra clear or precise.  It can sound stiff or formal if the aspirated t always used.