We do that when the sound before is unvoiced.

当其前面的音为不发音时，我们会这样做。

And a 'th' at the end of a word is usually unvoiced.

单词末尾的“th”音一般也都是清辅音。

So the 'th' at the start of content words is usually unvoiced.

所以实义词之前的“th”一般都是清辅音。

It's unvoiced because there's no vibration here.

它是无声的，因为这里没有振动。

If the first one is unvoiced, the second one will sou nd unvoiced, no matter what you do.

如果第一个辅音是清音，无论怎样，第二个也会是清音。

Now if there is a 'th' in the middle of a word, before a consonant, it's usually unvoiced.

如果在单词的中间、辅音之前有一个“th”的话，通常都是清辅音。

They have the same tongue and mouth position but one uses air to make the sound, it's unvoiced.

它们的舌头和嘴的位置是一样的，但其中一个是不发音的。

The first one is voiced, the second one is unvoiced.

第一个是浊音，第二个是清音。

If you look it up in IPA, thank has unvoiced TH, AA as in Bat, NG sound, K.

如果你在 IPA 中查找它， thank 有清音 TH，AA 在 Bat 中， NG 声音， K。

Now we have an ed ending, the sound before is unvoiced so that ed ending is pronounced as a T.

现在我们有一个 ed 结尾，之前的声音是清音的，所以 ed 结尾发音为 T。