When a vibrating source of waves is approaching an observer, the frequency observed is higher than the frequency emitted by is lower than that emitted.

当振动着的波源逐渐靠近观测者时，测量到的频率比从波源发出的频率高。

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The source of this paradox is electronic anti-noise which creates sound waves to cancel out unwanted noise, such as rattles, blare, etc.

这种矛盾的根源是电子抗噪，它会产生声波来抵消不想要的噪音，如响尾音、刺耳的鸣响等。

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The Korean scientists, however, want to harness a different kind of power source: sound waves.

然而，韩国科学家想驾驭一种不同类型的能量源，那就是声波。

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Ambient radio waves have largely been ignored as a potential power source until recently, because the power of a broadcast radio signal rapidly decreases with distance.

ECONOMIST: Monitor