It's the same as when you hit two tuning forks at the same time, and hear a low-pitched oscillation in the background.

就像当你同时敲打两个音叉一样，你总会听到一个低沉的背景音振荡。

To get high quality quartz tuning forks, mechanical coupling error and frequency excursion by machining errors must be resolved.

加工高质量的石英音叉需要解决工艺误差导致的机械耦合误差及频率漂移等问题。

If you stay where you are and you don't move and I move these tuning forks, you will hear a different frequency and that's what we call Doppler effect.

如果我站在这里，你们不移动，我移动这些音叉，那么你们会听到不同，频率，这就是我们，所说的多普勒效应。