You are a musician and know well the nature of measures and rhythms; some are duple, others triple, and these two kinds of time may be divided further into slow, moderate, and quick. ---Thoinot Arbeau
To review: in metric or measured music, several pulse streams, related in simple 2:1 or 3:1 proportions, flow simultaneously. Often we can hear, tap, and count three, four, or five individual streams when listening to a clearly measured piece. This set of all tappable pulses is called the metric structure of a musical work. Features of the two most common metric structures, duple and triple, are presented in the next few pages, followed by a discussion of other metrical organizations.