[For the benefit of those who've never heard either the word "organum" or the expression "oblique organum", the first refers to the singing of a melody in two voices, at the interval of a 5th, and the second refers to the practice of singing in organum, but breaking the parallel fifths to avoid either notes which are not in the mode or which would make 'forbidden intervals']
Has anyone tried this morning's Communion Antiphon, Amen dico vobis using either fixed or oblique organum?
In music history the term organum refers to a range of early polyphonic practices from the 9th to 12th centuries. In the earliest, simplest form, the two voices started on a unison and then split, one voice maintaining the starting pitch while the other ascended stepwise along the melody until (generally) the interval of a fourth was reached; there might then be a series of parallel fourths (generally not fifths) until the parts re-converged on a unison at the cadence. (See for instance the excellent article in The New Grove.)
I'm only familiar with the kind MarkS describes, done on a psalm tone, in which the lines diverge mirror-like and then return to each other. It's very cool.
Diverging "mirror-like" is actually different. "Oblique" refers to one of the two voices staying on the starting pitch (same note) until a 5th (or 4th) is reached by the melody and then proceeding in parallel.
Try singing "O come, o come, Emmanuel" by singing "O come, of come, Em-" on the starting pitch and then proceeding at a 5th below the melody from that point on.
Given that on the syllable "-men" there is a half step (from la to te) and no comparable half-step a fifth lower, would one sing the fifth (and thus add a flat to the lower note) or stay on re (allowing a minor sixth)?
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