Quadruplum definitions

quadruplum

(1) the fourth voice to be composed; in organum and the early motet, it is found above the triplum, duplum/motetus, and tenor.
Found on https://www.arlima.net/the-orb/encyclop/culture/music/orbgloss.htm

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quadruplum

(2) in organum, a piece which has a fourth `quadruplum ` line can be called an `organum quadruplum ` or `quadruplum ` for short. Perotin wrote two quadrupla: `Viderunt omnes ` and `Sederunt. `
Found on https://www.arlima.net/the-orb/encyclop/culture/music/orbgloss.htm

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