The Voice of Notre-Dame de Paris

Christophe d’Alessandro, CNRS research director at the Jean le Rond d’Alembert Institute and head of the "Lutheries – Acoustics – Music" team, is also the titular organist of the Sainte-Élisabeth church in Paris. He is part of the National Architecture and Heritage Commission, which has been consulted on the restoration of this historic instrument.

Two organs once resounded under the vaulted ceilings of Notre-Dame: the grand organ, located in the gallery and classified as a historic monument, and the choir organ, a smaller instrument positioned near the transept crossing where the spire collapsed during the fire.

“Based on initial observations, it seems that the choir organ was more affected by water than fire, while the grand organ was largely spared. Protected by a stone slab, it was not flooded, its pipes didn’t melt, and its console remains intact, aside from heavy dust,” explains Christophe d’Alessandro.

Although further assessments are still pending, the researcher asserts that “nothing appears to be irretrievably lost so far.” However, dust, soot, and the intense heat from the fire could have impacted the instrument.
“The organ’s restoration can only begin once the building is ready to house it again,” notes d’Alessandro, as masonry work in the cathedral could otherwise damage it. “Encasing the organ is being considered during construction, which is less risky than dismantling and removing it. The organ will also need cleaning and tuning. Each of its 7,374 pipes is adjusted to within a hundredth of a millimeter for harmony. This restoration will be a massive undertaking lasting several months, or even years, depending on the extent of the damage, as there is currently no electricity to test the instrument’s functionality,” the researcher elaborates.

A Monumental Instrument

As wide as the cathedral’s nave and over 20 meters high, the Notre-Dame organ is one of the largest in France. This exceptional instrument consists of numerous components, including a forest of 7,374 wooden or metal pipes, accessible for exploration, windchests supporting the pipes, bellows supplying air, and the keyboard console.

The console serves as the organist’s control center, combining five manual keyboards, a pedal keyboard, and over a hundred stop knobs to activate specific sets of pipes.

“When a stop is pulled, it activates a row of pipes. Each row has a distinct timbre, sometimes named after orchestral instruments (oboe, flute, trumpet, cello, etc.), and these can be blended or contrasted with other stops,” explains d’Alessandro.

A Witness to History

Situated beneath the western rose window, this monumental organ benefits from the cathedral’s extraordinary acoustics, which amplify its sound for up to eight seconds. It is the “voice” of the cathedral. From the wedding of Henri IV to the coronation of Napoleon and the liberation of Paris in 1944, the gallery organ has accompanied Notre-Dame through pivotal moments in French history.

“Present at all major events at Notre-Dame, the grand organ, like the bells, represents the cathedral’s sonic identity. People came from around the world to hear it, and the most renowned organists have played it,” emphasizes d’Alessandro.

The traces of previous restorations reflect the history that has shaped the organ. Built in the early 15th century on the stone gallery above the west portal, the organ has evolved over the centuries.
“The organ is a palimpsest,” explains the researcher. “Different eras are layered within it. The case dates from the 18th century, the pipes from the 17th, 18th, 19th, 20th, and even the 21st centuries. Successive restorations have always aimed to modernize the instrument by adding new stops, computerizing the mechanisms, and improving the console’s ergonomics.” The last renovation of the organ occurred in 2012, taking two years. During this time, the instrument was completely dismantled, with its digital transmissions updated, old mechanisms restored, facade pipes refurbished, and the console entirely replaced.

To restore the grand organ’s sound to its pre-fire glory, experts can rely on the work of the "Lutheries – Acoustics – Music" team. This group, part of Sorbonne University’s Collegium Musicæ, specializes in reconstructing lost or altered acoustic spaces using virtual reality and computer simulations. Two acoustic measurement campaigns were conducted in the cathedral in 1987 and 2015. With these measurements, Brian Katz, a 3D audio specialist, created a digital model of Notre-Dame’s acoustics, which will serve as a reference for the restoration.