The organ of the John Cage organ project is illuminated prior to a ‘sound change’ at the partially ruined Buchardi Church in Halberstadt, Germany, Saturday, Sept. 5, 2020. Since 2001 an interpretation of the music peace ‘Organ/ASLSP’, As Slow As Possible, by US composer John Cage is performed on the organ. The total duration of the piece is planned for 639 years without any stop.

The organ of the John Cage organ project is illuminated prior to a ‘sound change’ at the partially ruined Buchardi Church in Halberstadt, Germany, Saturday, Sept. 5, 2020. Since 2001 an interpretation of the music peace ‘Organ/ASLSP’, As Slow As Possible, by US composer John Cage is performed on the organ. The total duration of the piece is planned for 639 years without any stop.

Organist Julian Lembke, center, changes a pipe of the organ of the John Cage organ project during a ‘chord change’ at the partially ruined Burchardi Church in Halberstadt, Germany, Saturday, Sept. 5, 2020. The performance of the “ORGAN/ASLSP,” or As Slow As Possible, composition by John Cage began in September 2001 at the church in the eastern town of Halberstadt and is supposed to end in 2640. The last chord change was in 2013.

Singer Johanna Vargas changes a pipe of the organ of the John Cage organ project during a ‘chord change’ at the partially ruined Burchardi Church in Halberstadt, Germany, Saturday, Sept. 5, 2020. The performance of the “ORGAN/ASLSP,” or As Slow As Possible, composition by John Cage began in September 2001 at the church in the eastern town of Halberstadt and is supposed to end in 2640. The last chord change was in 2013.

People, wearing face masks to protect against the coronavirus as they line up to attend a ‘chord change’ of the organ of the John Cage organ project at the partially ruined Burchardi Church in Halberstadt, Germany, Saturday, Sept. 5, 2020. The performance of the “ORGAN/ASLSP,” or As Slow As Possible, composition by John Cage began in September 2001 at the church in the eastern town of Halberstadt and is supposed to end in 2640. The last chord change was in 2013.

People, wearing face masks to protect against the coronavirus as they line up to attend a ‘chord change’ of the organ of the John Cage organ project at the partially ruined Burchardi Church in Halberstadt, Germany, Saturday, Sept. 5, 2020. The performance of the “ORGAN/ASLSP,” or As Slow As Possible, composition by John Cage began in September 2001 at the church in the eastern town of Halberstadt and is supposed to end in 2640. The last chord change was in 2013.

The organ of the John Cage organ project is illuminated prior to a ‘chord change’ at the partially ruined Burchardi Church in Halberstadt, Germany, Saturday, Sept. 5, 2020. The performance of the “ORGAN/ASLSP,” or As Slow As Possible, composition by John Cage began in September 2001 at the church in the eastern town of Halberstadt and is supposed to end in 2640. The last chord change was in 2013.

People, wearing face masks to protect against the coronavirus as they line up to enter the partially ruined Burchardi Church after a ‘chord change’ of the organ of the John Cage in Halberstadt, Germany, Saturday, Sept. 5, 2020. The performance of the “ORGAN/ASLSP,” or As Slow As Possible, composition by John Cage began in September 2001 at the church in the eastern town of Halberstadt and is supposed to end in 2640. The last chord change was in 2013.

HALBERSTADT, Germany (AP) — Hundreds of fans attended a special kind of musical happening Saturday at a church in Germany: a chord change in an organ piece that is supposed to last for an entirety of 639 years.

The performance of the “ORGAN/ASLSP,” or As Slow As Possible, composition began in September 2001 at the St. Burchardi Church in the eastern town of Halberstadt and is supposed to end in 2640 — if all goes well.

The music piece by the American composer John Cage is played on a special organ inside the medieval church. The last sound has been the same one for the last six years and 11 months, and therefore the chord change Saturday was a big event among fans of the John Cage Organ Project.

A chord change means that the sound of the organ pipes changes either because new sounds are added or existing sounds end. On Saturday, two new organ pipes were added.

Organizers say the performance is “one of the slowest realizations of an organ musical piece.”

A compressor in the basement creates energy to blow air into the organ to create a continuous sound. When a chord change happens, it’s done manually. On Saturday, soprano singer Johanna Vargas and organist Julian Lembke changed the chord.

The new sound reminded some listeners of the metallic buzz inside a big ships’s engine room.

The next chord change is planned for Feb. 5, 2022, the German news agency dpa reported.

When the piece officially started on Sept. 5, 2001, it began without any sound. It was only on Feb. 5, 2003, the day of the first chord change, that the first organ pipe chords could actually be heard inside the church.