Up close, the Golden Gate Bridge is not the graceful beauty it seems from a distance. It is noisy. It hums with traffic and bellows sometimes with the sounds of foghorns.

At other times, the wind whistles through its cables, and in the background is a constant sound of the cries of seabirds, not to mention the Pacific Ocean.

Musicians look at the bridge differently. Mickey Hart, the former Grateful Dead drummer, sees the Golden Gate Bridge as a "giant wind harp." He plans to be at Crissy Field on Sunday evening, the bridge's 75th birthday, to perform an original composition.

The bridge will be the star. "The most famous bridge in America," Hart said, "is actually a musical instrument."

Hart will be performing on a 23-foot-long stainless steel model of the Golden Gate Bridge, built by engineers at the Exploratorium, accompanied, as it were, by recorded sounds of the bridge itself, a process he calls "sonification."

Back in 1987, to celebrate the Golden Gate's 50th anniversary, members of the San Francisco Synthesizer Ensemble produced a "50th Anniversary Suite" by hitting components of the bridge with rubber mallets. They recorded the sounds, remixed them and came up with a CD.

The difference, said Doug McKechnie of the Synthesizer Ensemble, is that Hart is using the bridge sounds as an accompaniment to his opus, while McKechnie and his group are again using the bridge itself to make music, as on the new single "A Day in the Life of the Golden Gate Bridge."

McKechnie and his group, which includes Paul de Benedictis, a music composer and computer technocrat, have come up with an application for the iPhone and iPod that allows users to "play" the bridge's suspender ropes as if they were strings on a harp.

The suspender ropes are cables that run off the two main cables and hold up the bridge deck. The suspender ropes are of different lengths - short at the ends of the bridge and in the center. But near the towers, they are 500 feet long. When tapped - say with a mallet - each suspender rope gives out a different sound.

The long ones make a sound something like "PeeeouEEEEeeeowwwwwiiee."

McKechnie also demonstrated the sound the south tower makes when struck with a mallet, a sort of dull clunk, a serious, purposeful sound, which you might expect from something riveted and 746 feet tall. He said the light standards make a different sound, as does the bridge railing, which gives off a hollow "gonggggg" sound when tapped.

The cars, trucks and buses traveling on the bridge also make their own sound, a bit like a loud hiss. At the expansion joints, the vehicles make a fast, brisk sound that is a bit like the "rivvett" cry of a frog, only much faster, like a frog on speed. Even a layperson can make this out by stopping on the bridge sidewalk and listening: "rivvett ... rivvett ... rivvett," a pause, then a "rivvett-klunk" as a truck passes over the joints - metal devices that move as the bridge deck expands and contracts.

At the same time, the bridge trembles a bit, which is its own sound.

Mix in the foghorns, a sort of fugue that is the signature sound at the Golden Gate, twist and turn the sounds electronically, use multiple tracks and you hear the frequencies and the harmonics of the bridge. The result is something McKechnie calls "very musical."

Do not think, however, that anyone can go out and hit the bridge with a rubber hammer in the name of science and music. The authorities take a dim view of this. McKechnie and his associates found this out years ago, when their first attempt to record the bridge sounds drew a pair of California Highway Patrol officers with drawn guns.

Something similar happened to Hart, back when he had long hair and was a nobody. He was "unceremoniously escorted off" the bridge twice, he said. "Once in handcuffs."

But time and science marched on, and now a remastered Synthesizer Ensemble CD featuring the "50th Anniversary Suite" is on sale at the new Golden Gate visitor center.

The Synthesizer Ensemble's app, called "Play the Golden Gate Bridge," is available on the iTunes app store.

Golden Gate Bridge Festival

Former Grateful Dead drummer Mickey Hart and his band will perform his new opus inspired by the sounds of the Golden Gate Bridge at 10 p.m. Sunday at Crissy Field. Admission is free.
