Now, the " DUB" sound — and, just to be clear, I am not talking about dubstep sounds — that's the aortic and pulmonary semilunar valves closing at the start of diastole.

现在，“DUB”音——澄清一下，我不是在说 dubStep 音——是主动脉和肺半月瓣在舒张期开始时关闭。