Pronunciation: American /t/ pronounced like /d/

https://www.youtube.com/watch?v=aeks05fGpas&feature=youtu.be

When t is Between Two Vowels

When a t is between two vowels, it is generally pronounced like a fast /d/ sound. The tip of the tongue touches the upper gum ridge.
A t becomes a “fast /d/” in the following cases:

A. Between two vowels:

We don’t say:                      We say:
better                                  bedder

B. Before an “l”:

We don’t say:                       We say:
little                                     liddle

C. After an “r” and a vowel:

We don’t say:                      We say:

party                                   pardy

forty                                    fordy

For example:

matter              letter                betty             botter

butter               settle                bottle            article