Performers and visitors to the famous gothic cathedral in the midst of the River Seine may find some subtle differences to the way sound bounces around its walls.

The Cathedral of Notre-Dame de Paris has borne witness to many turning points in history. The building's striking gothic stonework has stood sentry on an island in the midst of the River Seine since the late 12th Century as coronations, wars and revolutions have unfolded in its shadow. What you might not realise, however, is that the cathedral has played a key part in shaping the music you hear when you turn on the radio or stream a playlist.

Notre-Dame was, for a brief time, the beating heart of a musical revolution – one that changed music forever and laid the foundations for many of the songs we listen to today.

Up until the middle of the 12th Century in Medieval Europe, it was common to hear the haunting melodic chants of the clergy echoing through churches and cathedrals. Gregorian chant, or plainsong, was the musical style of the day, where sacred texts were sung either by a single voice or a choir in unison – something known as monophony.

But faced with the Notre-Dame's soaring nave, ribbed vaults and towering columns, a group of composers began to try something different to take advantage of the way sound rattled around inside the building. They introduced multiple lines of melody simultaneously to produce elaborate polyphonic arrangements, or motets – the early beginnings of a musical texture that is a common feature in modern music, from jazz to pop and hip-hop.

"They had to figure out a way to sing in there that worked with the architecture," says Brian Katz, an expert on acoustics and research director at the Institut D'Alembert at Sorbonne University in France.

Katz has spent more than a decade studying the acoustics of Notre-Dame, painstakingly hanging microphones and taking measurements to reconstruct what it would have sounded like to play music, sing and preach inside the cathedral at different points in its evolution. Now, Katz hopes to return with his microphones and equipment as Notre-Dame enters a new phase. The cathedral recently reopened for the first time after the devastating fire that destroyed the roof, spire and much of the interior of the cathedral in April 2019. The reconstruction – which reportedly cost €700m (£582m, $758) – saw the building restored stone by stone to how it had been before the blaze.

But Katz believes something may have changed – the way it sounds.

"It's hard to tell exactly how it has changed but we expect it to be more reverberant," he says. Katz has visited Notre-Dame several times to attend masses and performances since it officially reopened on 7 December 2024. The experience has been "incredibly moving", he says.

But as he sat in different parts of the cathedral, he also couldn't shake the sensation that it sounded different. A new sound system and the extensive cleaning of the organ's 8,000 pipes during the restoration work have certainly contributed to that, but he believes that the way sound interplays with the fabric of the building itself is also subtly different.

"The organist has already stated that it will take a bit of time to adapt to the subtle changes in the restored acoustics and organ," he says. "This is very typical of say a new concert hall, where the resident orchestra – and audience – need a few months to adjust to new conditions. The space is like an instrument, and one needs to become familiar with it to get the best out of it."

Katz and his research group at Sorbonne University have worked alongside the architects and builders charged with........

© BBC