Saturday, many New Yorkers are marking the third anniversary of the September 11 attacks, when terrorists crashed two hijacked airliners into the World Trade Center towers, causing an inferno that collapsed both buildings and killed over 3,000 people.

Many touching artifacts survived the attacks on New York: a pair of fireman's boots, a gnarl of twisted steel taken from the wreckage, missing-persons flyers posted by family members. But that tragic day also produced a wealth of sound recordings that recall the event with stinging immediacy.

Merely mention the date Tuesday September 11, 2001 to most New Yorkers and images of burning towers, anguish, heroism and death immediately come to their minds.

The violence of that day lends an eerie quality to what came immediately before, like this otherwise forgettable radio broadcast just 45 minutes before the first plane hit.

"Good morning. Sixty-four degrees at eight o' clock. It's Tuesday September Eleventh. I'm Lee Harris. Here's what's happening. It's Primary Day in New York City, voters are deciding?" a radio announcer said on that fateful day.

"It's going to be a beautiful day today. Sunshine throughout. Really a splendid September day -- the afternoon temperature about 80 degrees. Great weather for the primary election? Tomorrow, sunny and very nice," another radio announcer said.

Those recordings and others were collected by the Kitchen Sisters, two independent radio artists, as part of their "Sonic Memorial Project." It's an audio history of the Twin Towers and the neighborhood where they stood. The recordings also form part of a self-guided audio tour produced by a small company named "Soundwalk."

Soundwalk spokesman Michel Sitruk, a Frenchman who became a New Yorker years ago, spoke to me in the churchyard at Saint Paul's Chapel, perhaps 100 meters from Ground Zero, where the Soundwalk audio tour begins.

"We came back regularly to Ground Zero like a lot of New Yorkers did and we realized that people come here today for two reasons: they come here to pay their respects, and they come here to understand," he explained. " And they come here to understand in a more direct kind of way than they could have experienced through the television.

I mean, we've all seen the images over and over again. And we felt we could really offer the people who come here from anywhere in the world a chance to hear what these voices had to say. It's obviously quite painful to listen to."

At 8:46 a.m. on September 11, American Airlines flight 11 crashed into the World Trade Center's north tower. From the 101st floor of the south tower, a man named Sean Rooney left a phone message for his spouse.

"Hey Beverly, this is Sean," he said. "In case you get this message - there's been an explosion in World Trade One that's the other building. It looks like a plane struck it. It's on fire at about the 90th floor. And it's? it's? it's horrible. Bye."

Meanwhile, a second plane, United Airlines Flight 175, had been hijacked and was headed for the World Trade Center's other tower the one Mr. Rooney was in. Here is a phone message left by a passenger, Bryan Sweeney, for his wife Julia.

"Hey Jules. This is Brian. Listen. I'm on a plane that's been hijacked," he said. "If things don't go well and it's not looking good I want you to know that I absolutely love you. I want you to do good, go have good times. The same to my parents and everybody, and I just totally love you. And I'll see you when you get here. Bye, babe. I hope I call you."

Here is a second phone message from Sean Rooney from the 101st floor of the south tower.

" Hi. This is Sean again. Looks like [seems like] we'll be in this tower for a while," he said. "It's? it's secure here. [PA system] I'll talk to you later. Bye."

That message was received on September 11 at 9:02 a.m.

At 9:03 a.m., United Airlines flight 175 hit the south tower. A reporter named Steven Manning had just emerged from the subway station on Chambers Street nearby. Here is the message he left for the Kitchen Sisters before playing his recording of the streetscape as the first tower collapsed.

"I raced toward the twin towers. I could already see panicked people pouring out the doors when we heard this unbelievable sound and ]we] looked up and saw that Tower One was cracking open," he said. "But maybe this would capture it a little better."

Today, three years later, it is calm calm for New York at the spot near ground Xero where Mr. Manning made that recording. I asked Soundwalk's Michel Sitruk to go there with me.

"So what about now, what do you hear?" I asked.

"I hear New York City coming back to life, actually," he responded. "And I guess we can draw a parallel with that morning, which was also a beautiful day like this one. It's so good to feel it coming back to life. Everyone's rushing to work. It's lunchtime. There are throngs of people on the streets. And I see tourist buses, which is always a good sign!"