2 September 2010 Last updated at 10:35 ET

Musician Nick Franglen creates bridge symphony

By Tim Masters Entertainment correspondent, BBC News

Nick Franglen and his theremin are spending 24 hours under London Bridge

Nick Franglen is using London Bridge and its human traffic to create a 24-hour piece of music - armed only with a theremin and an espresso machine.

Tucked underneath the arches - surrounded by effects pedals and a mixing desk - Franglen has already been on the go for 10 hours.

Since midnight, the musician has been using an electronic instrument called a theremin to create what he calls "washes of sound" which are looping out of a nearby speaker.

The unwitting players in his Hymn to London Bridge are the pedestrians passing overhead who trigger a sensor that briefly cuts the flow of music. The project lasts a full 24 hours.

"It's about an incredible surge of humankind doing their thing above us," says Franglen.

"What I'm trying to do is to get some idea of what that human movement really feels like - a sense of the ebb and flow of the human traffic."

He adds: "It was really beautiful at about 3 a.m. - there were very few interruptions up top and it was really enchanting. Then the pedestrian traffic started to impose itself on this piece of music. It was overwhelming."

Ghost walker

Nick Franglen has been making experimental music over the past few years with Blacksand

Franglen is one half of the electronica duo Lemon Jelly. Born in north London in 1965, he has worked as a session musician for Primal Scream, Bjork, Pulp, and Blur.

He's also made a record with Star Trek legend William Shatner.

Franglen has produced albums for former Velvet Underground member John Cale and Badly Drawn Boy, and written scores for film and TV. His other project is the experimental electronica duo Blacksand, which he formed in 2006.

Given that Blacksand's album Barn was launched at the bottom of a mine in Wiltshire, Franglen is no stranger to creating music in unusual places.

"There's something very beautiful about playing improvised music in a space that's got an unusual ambience," he says, recalling other gigs in a Cold War-era Soviet submarine, and serenading the dawn on Hampstead Heath.

The whole of Hymn to London Bridge will go up on Franglen's website, where it is also being live-streamed throughout 2 September.

What is a theremin?

• An early 20th century instrument, played without contact
• Named after its Russian inventor, Professor Leon Theremin
• Sound is produced by moving the hands in the space around the instrument's antennae
• Its eerie sound appears on the soundtracks of The Day The Earth Stood Still (1951) and Hitchcock's Spellbound (1945)
• The theremin is still in use today by groups such as space rockers Hawkwind

"What I'd really like is anyone who crossed the bridge today to go and have a listen - and feel that they contributed," the musician says.

One of those crossing the bridge on Thursday morning was Rosemary Clarke, visiting London from South Africa for a family wedding.

Like most of the people crossing the bridge, she is completely unaware of her walk-on part in the musical project.

"I've been a church organist for nearly 30 years, so I don't mind at all," she says. "It's great, it's someone's creativity - that's what music is all about."

Franglen adds: "I like that sense of collaboration. It's particularly poignant in the middle of the night when there are no pedestrians for several minutes, but then someone crosses and it's like the ghost of someone above."

He plans on getting through the rest of the day with the help of the espresso machine set up next to the theremin.

"Thank you, coffee, for doing your thing!" he laughs. "But right now I feel as fresh as you like. It's not been an ordeal in any way."

A filmed loop of the performance will be projected along the river during the Thames Festival on 11-12 September.