Paywalled, of course, but if you subscribe or know someone who can offer you a gift link out of their monthly allotment of gift links, the NY Times has just posted a fabulous interactive long form piece (with spatial audio) on the efforts to document and restore the acoustical sound of the cathedral:

https://www.nytimes.com/interactive/2023/03/03/magazine/notre-dame-cathedral-acoustics-sound.html

"To test the acoustics of the space at different points in the cathedral’s history, he and his team examined how a performance of “Viderunt Omnes,” by the French composer Pérotin, would have sounded. Pérotin was part of the Notre Dame school of composition, which developed contemporaneously with the building of the cathedral in the 12th and 13th centuries. The Notre Dame school was polyphonic, and in an organum like the “Viderunt,” you might hear a chant with more colorful upper voices, florid moments that illuminate the prayer, like golden margins on a piece of vellum. To understand the interplay between the song and the historical acoustics, the group brought in experienced medieval singers to perform in an echo-free chamber. They have been testing the ornate lines of “Viderunt Omnes” in relation to the complex acoustics of the vaulted cathedral, which at the time of the song’s earliest known performance, in 1198, was yet to be completed."

[interactive examples provided from different locations]

"Any change in a space can have a large effect on sound. Despite the size of the cathedral, or perhaps because of it, “a very small change in some material, since it is propagated over hundreds of square meters, can have more of an effect than you would imagine,” Katz says. In comparing acoustical measurements from 2015 with ones taken in 1987, Katz found that even though the cathedral had not undergone any major alterations, the acoustics had changed. The likely culprit turned out to be a carpet strip that had been added to reduce the noise of footfall from tourists visiting during Mass. “That installation of the carpeting reduced the reverberation time a noticeable amount over that period,” he says. “This was remarked by the organist and the choir.” The properties of materials like these will shape the sound of the cathedral when it is restored. “In the stone, you know, are they considering different quarries? Are they considering different materials?” Katz says. “Are they considering different finishes? And all of those things could have an impact — is it a rough, porous stone, or is it more of a polished stone?” "

" . . . Though the decision was made to restore the cathedral to how it looked before the fire — including Viollet-le-Duc’s iconic spire — Pardoen’s project will span the building’s nearly 900-year history, in a kind of auditory excavation, an archaeology of sound. For Notre Dame, she is creating eight soundscapes that capture different periods in the life of the cathedral, among them: 1170, when the choir was first being built; the beginning of the 13th century, when the full building was completed; and the present era. These moments represent turning points in the building’s history, and the combined soundscapes will illustrate this history in a new way."