From MusiCAD

A duplet consists of two notes that together have the duration of three notes. Usually you will not use a real duplet but two dotted notes in a row (which have exactly the same duration!)

duplet and quadruplet

In MusiCAD you also make a duplet by entering two dotted notes one after the other and cluster them (if necessary).

You can cluster two duplets into a quadruplet, two quadruplet into a octoplet

See also