As far as I understand, the music of the French school's masses first and foremost served the purpose to decorate and embellish the words, and not to express them in the way we percieve the word "express" since the romantic age. Just like the decorated capitals in manuscripts from that time. This is my main objection to Schmelzer's interpretation, which is anything but beautiful and instead expressive in a kind of romantic sense. And his claimed intention of making Machaut's mass sound "new" to us is IMO besides the point. Think of all the great music which sounded new to the first listeners. Should we distort our interpretations of this to make it sound new to us again? What about the Choral symphony or Le Sacre du Printemps? I think Schmelzer has taken his arguments out of the air, with the purpose of creating a sensation. With all the existing fine recordings of Machaut's mass it is of course difficult to make a new, which creates sensation by informed arguments.
I have mixed feelings about Schmelzer's recording: on the one hand it is overall a beautiful sounding performance; on the other hand it is as you say, an aberration of the performance practice of this work; and his pretentious essay does not help his case, imo.
I suppose you think of the G sharp in bar two of the Kyrie.
The edition by Lucy Cross (Ed. Peters 1998) which is intended as a score for practical performance, has a lot of "adaptions", In this edition the note is G sharp (sharped Causa Pulchritudinis). The rules of musica ficta were of course meant to be used in performance, which she explains in a chapter dealing with musica ficta.
I have not seen her score, but will seek it out. The g# may "solve" one problem (although I find the E minor tonality to be pleasing) but creates a different one with the c in the motetus creating a E augmented vertical sound. I would like to understand why she chose to sharp the g whereas Leech-Wilkinson and others did not. Also the tenor, which carries the chant, has a g natural which should not be changed. g against g# seems very odd.
Granted during Machaut's time they were thinking linearly and not vertically, in fact tolerating "illegal" contrapuntal movement between internal voices as long as the counterpoint was pure in relation to the bottom voice at the time. Still I wonder if that augmented chord might have been extraordinary for them.
In the bar in question she has also sharpened the g in the tenor and the c in the motetus, I suppose because of the rising steps in all three parts.
I found a review of the Cross score here:
Reviewed Work: Messe de Nostre Dame [For] Mixed Voices by Guillaume de Machaut, Lucy E. Cross
Review by: Virginia NewesNotes
Second Series, Vol. 57, No. 3 (Mar., 2001), pp. 717-721
Published by: Music Library Association
Stable URL: http://www.jstor.org/stable/900841
The conclusion of the reviewer is that this score should not be recommended because of the liberal application of sharps (which are all put inside the score instead of above as is usually done with editorial decisions).
I will keep looking for other opinions of this score.
Interesting, thanks for bringing it to my attention.