Chinese · Pronunciation Guide
doe with no puff of air and the pitch held high and flat. The vowel starts less rounded than English "oh".
dōu
No rule reaches this syllable. What it does do is protect its neighbours: as an adverb it sits between a subject and a verb, and being a first tone it breaks up what would otherwise be third-tone sequences. In wǒmen dōu, the pronoun keeps its dip precisely because dōu is high and level.
Listen: 都
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我们都是学生。
Wǒmen dōu shì xuésheng.
We are all students.
Listen: 我们都是学生。
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我们都是学生。 gives a nice alternation: wǒ dips, men is toneless, dōu is high, shì falls, xué rises, sheng is toneless. Every adjacent pair does something different, and the word 都 is the high plateau in the middle that everything else moves around.
Aspirating the d turns it into tōu, a different word, and English speakers aspirate initial stops almost without exception. Keep the breath in. The other error is letting the level tone fall away at the end, because the vowel glide feels like it should resolve downward; the mouth closes toward "oo" but the pitch must stay where it started.