I would like to start with my schola singing of some pieces of organum composed by Leoninus. Do you know where I can find scores (to download or to buy or to copy)?
If you want the whole thing and have access to a good music library, this is it:
Le Magnus liber organi de Notre-Dame de Paris / publie sous la direction de Edward H. Roesner. Monaco : Editions de l'Oiseau-Lyre, c1993-
The multi-volume scholarly edition is out of price range even for some libraries. The rhythmic notation of the time, even in these new editions, is a challenge to modern performers. A less expensive alternative is The rhythm of twelfth-century polyphony of W. Waite, which contains rhythmic transcriptions of some of the more salient examples of organum from the Magnus Liber.
Remember that the Magnus Liber does not really exist. We only know it from a reference by Anonymous 4. Even then, we can't assume it is a title, since it just means "Big Book of Organum". Roesner collated music from later manuscripts in Florence, Wolfenbuttel, Madrid, Paris and Burgos (Las Huelgas) to reconstruct the collection as best one can now.
I sang a piece from the Magnus Liber Organi for my concert in August as a duet with another soloist with her master's in voice, and small organ playing the bottom line. The music looked fairly straightforward, but upon piecing it together, we discovered it was quite complex. The result was very neat, especially with some improvised drum rhythms from an Arab drum, but it really challenged two fairly seasoned soloists in the process.
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