We have the convention of music of writing this symbol indicating the beat-carrying unit of four so I'm writing a four underneath each of these.

我们有一个约定俗成的书写格式,来表示四拍一单元,所以我在每行这里的下面写上一个四

耶鲁公开课 - 聆听音乐课程节选

Okay. So here we have a series of groups of two quarter notes.

好的,我们有好多的单元,由两个四分音符组成

耶鲁公开课 - 聆听音乐课程节选