The site's Vietnamese is Hanoi's: six tones, the glottal catch on ngã and nặng, and the three consonant mergers the spelling refuses to make — d, gi and r all /z/, s and x both /s/, ch and tr both /c/. It is the accent of the news and the dictionary, and southerners find it clipped and a little cold.
Where: the Red River delta; the broadcast standard
The way in: Say 'Hà Nội' with the ội swallowed short and cut off — that nặng tone is the sound of the city.
Try a word
Anything the spelling engine can transcribe, the accent can move. Slow it down to hear the shape.
Even, syllable-timed and precise, with the six tones held cleanly apart. It sounds staccato to European ears because half the syllables end in an unreleased stop or a glottal cut.
What moves, one rule at a time
In the order the mouth applies them. Every before-and-after is playable — click the IPA. The pattern is the rule as the engine runs it, for the curious.
Vowels
a shortens before -nh and -ch
a(?=[ɲc](?:[˥˦˧˨˩ˀ]|$| )) → ă
When: before a final nh or ch
How: Cut the a short and let the tongue rise towards the palate as it ends.
The palatal codas pull the vowel forward and clip it: anh comes out close to 'ănh', sách close to 'săch'. The spelling writes a; the mouth says ă.