Hmm, that would be overnight between Saint John's and the Holy Innocents' feast-days, yes, that is right: I went out yesterday to the supermarket and while it wasn't as hard going as the same journey was two years ago (I think) when we had the last major winter storm (much more ice, then) it did none the less tire me out: the unevenness and constant changeability of the snow makes my hip work more arduously than it likes to-- it definitely prefers a level surface, no inclinations here, no depressions there.
Added three compact discs to my small collection yesterday (the shipping from somewhere in England-- I buy from Presto Classical more often than not-- takes almost always two weeks, a fortnight). The first, and the one I'm listening to now, is entitled Sacred Music from Notre-Dame Cathedral and features the composers Léonin (fl ca 1163-1190) and Pérotin (fl ca 1180-1225). The tracks currently playing are the setting of Psalm 97 in plainchant and then Léonin's settings of the Psalm 97 verses in organum duplum, which means one voice is singing the plainchant melody (or a transposition of it up or down) and the second voice is singing a different line of music-- either discantus, or organum purum. The purum is more or less recognisably a soloist elaborating on the melody; discantus, I haven't figured out yet-- it is in the same mode and sung in the same rhythm as the first, plainchant melody but beyond that I've not yet retained the information I've read....
In origin, it is a style of organum that either includes a plainchant tenor part (usually on a melisma in the chant) or is used without a plainchant basis in conductus, in either case with a "note against note" upper voice, moving in contrary motion. It is not a musical form, but rather a technique. The term continued to be used down to modern times with changing senses, at first for polyphony in general, then to differentiate a subcategory of polyphony (either in contrast to organum, or for improvised as distinct from written polyphony). By extension it became the name of a part that is added above the tenor, and later as the name of the highest part in a polyphonic setting (the equivalent of cantus, superius, and soprano). Finally, it was adopted as the name of the highest register of instruments such as recorders, cornets, viols, and organ stops.
One excellent feature on this part of the album is that each of the tracks records a single type of singing, so that one can easily identify when one proceeds from the plainchant to the organum duplum and back and forth as sung by the different groupings of voices. I must take a nap.