Timpani or as it's sometimes called a kettledrum, and it was playing two different pitches, actually sort of playing this pitch and this pitch, the octave and then the fifth.

定音鼓,或者有时称作半球形铜鼓,它正演奏两个不同的音高,实际上在演奏这个音高和另外一个音高,八度音阶和这个五度

耶鲁公开课 - 聆听音乐课程节选