Thanks for this interesting compilation. I've never taken part in the discussions how to sing chant, neither do I intend to start a new one. When I first learnt chant I was introduced to a kind of the Dom Mocquereau method, maybe even simplified I think. We ignored the ictus, for example. Now I sing in a schola which follows the Triplex. Tbh I find it a bit annoying because we certainly lose musicality over the attempt to follow the rhythm of the conductor. The schola can read only a small portion of the adiastematic neumes, so basically you have to know the chant by heart and watch the conductor while singing. Sticking together in a huge church is very difficult in this way. But I can certainly honor semiology – I think it's the same with historically informed practice in classical music – for revitalizing our performances. Its good for widening the imaginative space, so to speak.

The last performance (Ensemble Organum sings chant in this "oriental" way) is a reminder that even after all the semiological endeavours we should never claim that a certain interpretation is the way it was sung in the 9th century – it could be completely different and a few scratches in manuscripts can't tell the whole story.

Sorry when I was still too polemic against the Triplex :-) Most important is that we sing it and sing it for the praise of God.

PS: I admire the breath of all the singers! The repetitions always cost me so much air I could never sing such long lines without breathing!

Hmm, a couple others have also made comments about my recordings lacking dynamics. That is certainly not a deliberate decision on my part, but it is fair to say that it is "for practical reasons"—those being a schola with a mixture of professional and rather inexperienced amateur singers and not enough rehearsal time before recording! The proportional rhythm recordings on my channel are for demonstrative purposes and do not represent a "finished product." You will hear stray notes, misplaced syllables, poorly timed breaths, and all the other common problems of a parish schola. I am constantly having to remind my singers that the last note of a phrase in chant should be the softest; some of them still have a ways to go in basic musicianship. I would be delighted for someone with a very advanced ensemble to record from my edition, but that hasn't happened yet to my knowledge. Plus I've attempted to tackle the offertory verses first, which are arguably the most difficult and least formulaic chants in the repertory, instead of introits and communions. I know—excuses, excuses! ;)

Listening to the first minute of each of the recordings you shared, the one in the Solesmes style (Triors, I believe) is the only one that strikes me as having much in the way of dynamic contrast. There is a sense of an "arc" to each phrase in Marek Klein's Graduale Project recording, which is also what I strive for, but the other two strike me as more or less consistent in volume, without much variation. For an ensemble recording of the same chant in semiological style, this might be of interest:
https://www.youtube.com/watch?v=uDz2bgc-C0I

Here is my solo attempt (unlisted on YouTube):
https://www.youtube.com/watch?v=KX9eCACUYDE (link corrected!)

Again, this recording is for demonstrative purposes and does not represent a "finished product." I am certain that many others could do a much better job with it! My objective was to provide something quickly. I erroneously sang longs instead of shorts at -bi- in verse 4. As usual, upon listening to my own recording and following with the Graduale Novum, I noticed yet another inconsistency that I'll need to correct in my edition, namely the last two words of the second and thirteenth verses.

As for lack of historical evidence, there are significative letters in the manuscripts that refer to dynamics, but they are few and far between. The Solesmes style is mostly based on a nineteenth-century aesthetic.