他是逐渐注意到这种呼吸声的，因而他确实不知道它已经存在多久了。

And he had come to notice this breathing so gradually that he had really no idea how long it had been there.

youdao

现代应用较多的吸声层大部分是阻抗过渡式结构，但是厚度有限，无法满足低频吸声的要求。

Now most sound absorption layers are impedance transition constructs, which have been used widely, but their thickness is limit and cannot meet the need of absorbing sound at low frequency.

youdao

虽然双胞胎的房门关着，她们有节奏的呼吸声听起来像风暴在树林中呼啸，因为我还没有把自己训练得听而不闻。

Although their door was closed, the twins rhythmic breathing sounded like a storm rushing through the trees, for I had not yet trained myself not to listen.

youdao