Now there's a proper technique to make the purest sound.

想要使它发出最纯净的声音 需要特殊手法。

It begins with WH. This can be pronounced two ways:   first, a pure W sound.

它以 WH 开头。这可以通过两种方式发音：首先，纯 W 音。

" Roger lost his dog." Again, these ER sounds, in American English, turn into a more pure sound in the RP accent.

“罗杰失去了他的狗。 ” 同样，这些 ER 声音， 在美式英语中，变成了 RP 口音中更纯净的声音。

Then we have the UH as in BUTTER sound, but it's followed by a Dark L, so it's not really a pure sound.

然后我们有 BUTTER 声音中的 UH，但它后面是 Dark L， 所以它不是真正的纯声音。

Like R definitely changes the AW as in law vowel, it's not going to be a pure sound when R follows it in the same syllable.

就像 R 肯定会像法律元音一样改变 AW，当 R 在同一个音节中跟随它时，它不会是纯音。