How do you tune a cathedral organ?

It's "pretty excruciating" when they hit an out-of-tune note and the two-day process "can drive you out your mind", according to cathedral staff.

But how do tuners get Guildford Cathedral's organ, with roughly 4,000 pipes, sounding pitch-perfect?

"It's mainly hearing to be honest with you, I do all of this by ear," said Sam Keeler-Walker, the head tuner at Kent-based Mander Organ Builders.

If two pipes are being played together and they make a beating sound, then it means they need adjusting. "When it's one sound then it's in tune", he says.

One of the company's apprentice plays the notes while he sits in the organ adjusting slides to make the notes slightly lower or higher in pitch until they are in tune.

Mr Keeler-Walker said: "We have to tune an organ fairly regularly to make sure it's absolutely perfect at all times."

Katherine Dienes-Williams, the cathedral's organist described the instrument as a "high tech piece of equipment that needs regular maintenance".

"The possibilities of pipes going out of tune are endless," she said, and getting that quantity of pipes in tune with each other is "almost an impossible task".

The organist and master of the choristers said organ tuners "have such an intricate knowledge of how to fix problems and make it sound and speak within itself".

Large organs are sometimes built with groups of pipes (called divisions) associated with each keyboard (manual) in different places in the building.

The organ was transplanted from a church in Shipley, West Yorkshire and installed in Guildford during the final stages of the building's construction in 1961, according to the cathedral.

Ms Dienes-Williams told Secret Surrey the organ was a "last minute" afterthought and was installed in a "not ideal" way, leaving the "choir" division of the pipes a distance from where the choir sings from.

"You're left with this dichotomy," she said. "Do you play it loud enough so that the choir can hear you or do you play it more softly so that you're not offending the congregation?"

According to Guildford Cathedral, when it appointed Ms Dienes-Williams in 2008 she became the first ever woman to hold such a post in the Church of England.

She said it was a "tremendous feeling" and "great privilege" to play organs and see a space "no one else really gets to see".

Mr Keeler-Walker told Secret Surrey he wanted to encourage more people into organ building as it was "not a job that most people think about".

He said: "It has ruined organ recitals for me a bit because you are listening out all the time for anything that is slightly out of tune, but on the whole it's great."

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