Even with the advent of the Graduale Novum, there is still no performing edition of Gregorian chant for the Mass that gives singers all the necessary information about both pitch and rhythm.
The transcriptions at Gregor und Taube use only the St. Gall neumes, even when the Laon are available. The square note renderings distinguish in some cases between long and short notes (descending squares are long, diamonds are short), but not in the case of the pes, clivis, torculus, etc. The editor reproduces exactly what is written in the manuscript, even when the scribe is using shorthand (for example, short notes that are understood in context to be long) or has made an obvious mistake. The same is true of the Fluxus notation developed by Geert Maessen (as cool as it might look).
The transcription model suggested by Columba Kelly in his writing on The Role of Rhetoric requires perhaps as much specialized knowledge as the manuscripts themselves. Excellent as they are, his transcriptions are more useful for analysis than for performance.
I am suggesting a new model for transcription, one that requires the editor to make decisions based on comparison of more than one manuscript notation (if available), a familiarity with centonized melodies and possible cases of adaptation, and the performance practice and conventions in place at the time the chants were first notated.
For my transcription of the chant Vultum tuum (from a St Gall manuscript), I have indicated long, structural notes (what Kelly would call full syllabic value) with large noteheads and short, ornamental notes with smaller noteheads. The pitches in my transcriptions are generally the same as the melodic reading in the Graduale Novum, except in cases where there is disagreement between the various sources.
You will notice some other innovations. For one, I have dispensed with a special rhythmic indication for liquescence, leaving the proper pronunciation of the text up to the performer. (I have, however, underlined the relevant consonant or semivowel so that instances of liquescence can be identified and, if necessary, investigated further in the manuscript).
I will get into more detail on my transcription methods as I post more examples. In the meantime, I’d love to hear feedback from anyone who might like to try using these editions.