"It would primarily be found in Antiphonarium manuscripts as a responsory for Matins or first vespers of St. Dominic."

"I absolutely agree that it is impossible to ascribe a note name to the pitch; however, the resonance factor may provide a clue to the note that may have been sung. Cave paintings that had completely faded have been found using the resonance factor…"

"There is no way (really, no way at all) to say at what frequency a low B-flat would have been sung. Singers were free to adapt their singing to the ambitus of their own voice. There is no indication whatsoever of any link between a note name (or its…"

"I find this discussion quite intriguing for a number of reasons. The foremost is that a pitch near low Bb or even A is an important pitch in archaeoacoustics. Many cave paintings and rock paintings have very high reverberation rates when a tone of…"

"I will open a discussion for you at «Mélos et ses microtones» with this passus, so that you can also see, how Guido found the diesis on the monochord. You are welcome there! I do not think, that this treatise is very useful to discuss Domenican…"

"My mistake: I checked only the CSM edition of the Micrologus, but I then realized that GS indeed has a different text, which does include a mention of the diesis. Nicolas Meeùs said:
Oliver, could you be more specific about "Guido's passus about…"

"Oliver, could you be more specific about "Guido's passus about the diesis"? So far as I can tell, the word "diesis" can be found neither in the Micrologus, nor in the Epistola..."

"Dear David
As I'm sure you know, the Guidonian Gamut, which was the standard medieval scale system from about the mid-11th century, especially for plainchant (as opposed to polyphony), lacked the Bb (properly B-fa) in the lowest octave.



That is…"

"Yes. I was addressing only the question of whether the theoretical scale system ever admitted a low Bb. That is, of course, an entirely separate question from that of whether, and when, a low Bb was included in certain actual melodies."

"Let me add that we may be engaged in two separate discussions at once.
One is about the medieval theoretical "system", the Guidonian Gamut, which in principle did not include the low B♭ because the system did not extend low enough to allow building…"

"Hello, Fra Innocent -
Re. the music-theoretical aspect of the question -- 
As I'm sure you know, the Guidonian Gamut, which was the standard medieval scale system from about the mid-11th century, especially for plainchant (as opposed to polyphony),…"

"Thank you all for your helpful comments. The Dominican sources and the methodology of the project are outlined here: https://cantusop.wordpress.com/2016/08/22/graduale-op-introduction/ 
The two Dominican manuscript sources I'm primarily consulting…"

"I can only second the points made so clearly by Franz Karl Prassl. His point about transposition in the 2nd mode graduals is especially à-propos.  The Haec dies family, for example, is notated in the Graduale Romanum (and in many MSS) with final on…"

"Thank you to Franz Prassl for his answer. As I told, the b flat is perfectly right in the quoted examples . In any case, Guido suggests a transposition, and this confirms the b-flat !"

"Cher Père,
Pour commencer, je serais heureux de savoir sur quelles sources dominicaines vous travaillez...
J'ai l'habitude de construire des tableaux synoptiques, et cette méthode permet, dans beaucoup de cas, de connaître  l'avis de la tradition…"