Charlemagne had been carrying on his father’s mission to unite the chanting practices of western Europe under a single practice when he ran into some snags coordinating the singing between Rome and the provinces. Keep in mind that there was not a very good way to notate exact pitches during this period, so much relies on oral transmission when it comes down to the granular details of chanting. John the Deacon recounts (probably several decades after the fact) the struggles of getting the unruly Germans and Gauls to reproduce the chant the way they did it in Rome (N.B. John the Deacon was Roman and we’ll hear the story told on the other side of the Alps in a future episode of “Church Music is Just the Worst,” which is even spicier).

Of the various European peoples it was the Germans and the Gauls who were especially able to learn and repeatedly to relearn the suavity of the schola’s song, but they were by no means able to maintain it without distortion, as much because of their carelessness… as because of their native brutishness. For Alpine bodies, which make an incredible din with the thundering of their voices, do not properly echo the elegance of the received melody, because the barbaric savagery of a drunken gullet, when it attempts to sing the gentle cantilena with its inflections and repercussions, emits, by a kind of innate cracking, rough tones with a confused sound like a cart upon steps. And so it disquiets the spirits of those listeners that it should have mollified, irritating and disturbing them instead. Hence it is that in the time of this Gregory, when Augustine went to Britain, cantors of the Roman school were dispersed throughout the West and instructed the barbarians with distinction. After they died the Western churches so corrupted the received body of chant that a certain John, a Roman cantor (together with Theodore, a Roman citizen yet also archbishop of York), was sent by bishop Vitalian to Britain by way of Gaul; and John recalled the children of the churches in every place to the pristine sweetness of the chant, and preserved for many years, as much by himself as through his disciples, the rule of Roman doctrine. But our patrician Charles, the king of the Franks, disturbed when at Rome by the discrepancy between the Roman and the Gallican chant, is said to have asked—when the impudence of the Gauls argued that the chant was corrupted by certain tunes of ours, while on the contrary our melodies demonstrably represented the authentic antiphoner—whether the stream or the fountain is liable to preserve the clearer water. When they replied that it was the fountain, he wisely added: ‘therefore it is necessary that we, who have up to now drunk the tainted water of the stream, return to the flowing source of the perennial fountain’. Shortly afterward, then, he left two of his diligent clergymen with Hadrian, a bishop at the time, and, after they had been schooled with the necessary refinement, he employed them to recall the province of Metz to the sweetness of the original chant, and through her, to correct his entire region of Gaul. But when after a considerable time, with those who had been educated at Rome now dead, that most sage of kings had observed that the chant of the other Gallican churches differed from that of Metz, and had heard someone boasting that one chant had been corrupted by the other; ‘Again, he said, let us return to the source. Then Pope Hadrian [I], moved by the pleas of the king … sent two cantors to Gaul, by whose counsel the king recognized that all indeed had corrupted the suavity of the Roman chant by a sort of carelessness, and saw that Metz, in fact, differed by just a little, and only because of native savagery.

Quoted in With Voice and Pen by Leo Treitler, 155-6.