The original group of later-seventh-century compositions (as McKinnon dates them) can be identified by the comparison of two different groups of sources. The chants were taught to Frankish cantors in the last half of the eighth century at the order of King Pepin III and then of Charlemagne. Six Frankish Graduals, or manuscripts of Mass chant texts without notation, are still preserved, the earliest from a little before 800, the latest a century afterwards. These six Graduals have been edited by Dom René Hesbert in six parallel columns in the Antiphonale Missarum Sextuplex, published in 1935. The oldest Frankish Graduals that have neumes, or rudimentary notation, over the words can be dated around 900 to 930.

Meanwhile, chant was still sung in Rome without notation until 1071, when the Gradual of St. Cecilia in Trastevere was written, followed by two similar Graduals written in the twelfth and thirteenth centuries. The melodies of these three Old Roman Graduals (as they are known to scholars) are quite different in style from the chants of the tenth-century Frankish Graduals, though the texts and liturgical calendar are basically identical. If we compare the eleventh-century Old Roman Gradual with the tenth-century Frankish Graduals, it will be clear that the chants common to both repertoires were sung in Rome in the eighth century. McKinnon compares them in great detail.

While the Roman and Frankish chants have the same texts assigned to the same calendar of feasts, the chants are melodically different. Hence we must ask which of these repertoires better represents the eighth-century Roman practice. Most scholars now think that the chant melodies underwent changes in both traditions. Some think that the Old Roman Graduals are closer to the original Roman chant, but McKinnon thinks that the Frankish Graduals are closer, suggesting that Roman chant evolved considerably during the last three centuries of oral tradition.

In the Frankish kingdom many changes occurred. Additional chants were composed to fill in certain missing feast days. More important, the chants were notated in writing, first in neumes that indicated nuances of rhythm, later in staff notation that showed the melodies clearly. Influenced by the Greek system of eight modes, each chant was identified by its mode. In the case of antiphons, this established the psalm tone to be used for the following psalm. Tropes were inserted into the Ordinary and Proper chants of the Mass to explain the meaning of each feast day. Many new settings of the unchanging texts, the Ordinary of the Mass, were composed. In the most radical change, a second melody was added to the solo verses of some chants, at first only to the gradual and the alleluia verse. This was the beginning of polyphony, essentially a different kind of music than monophonic chant. But because polyphony was sung to strict rhythm, the nuances of the original chant rhythm were lost in a pattern of equal note values. Later, as slower tempos were adopted for chant to add solemnity to the service, the extended melodies on a single syllable, known as melismas, were removed from the chant. The word accents were shifted to coincide with the melodic accents, destroying the lightness of the chant rhythm. Because of these changes, the chant of the fourteenth to nineteenth centuries is considered debased.