SEATTLE — Some musicians spend 18 months working on a whole album. At Microsoft Corp., that's how long it took to perfect just four seconds of sound.

Of course, this isn't just any four-second clip. It's the sound — a soft da-dum, da-dumm, with a lush fade-out — that millions of computer users will hear every day, and perhaps thousands of times in total, when they turn on computers running Microsoft's forthcoming Windows Vista operating system.

To set the right tone — clean, simple, but with "some long-term legs," according to Microsoft's Steve Ball — the software maker recruited musician Robert Fripp.

Fripp, best known for his work with the '70s rock band King Crimson, recorded hours of his signature layered, guitar-driven sound for the project, under the close direction of Ball and others at Microsoft. Then, it was Ball's job to sort through those hours of live recordings to suss out just the right few seconds.

Fripp's involvement is not surprising. His occasional collaborator, Brian Eno, recorded sounds for Windows 95. Ball, the Microsoft group program manager for WAVE — Windows Audio Visual Excellence — has in the past been Fripp's student and business partner.

Ball, a self-proclaimed renaissance man who is both an engineer and a musician, considered the work of about 10 musicians for the project. Some of those people were influential in the final four seconds as well.

Redmond-based Microsoft seriously debated several other sounds before settling on the final startup sound about three weeks ago. The rejects included a longer, lusher clip and a quick, techno-sounding piece. While many people liked an upbeat ditty with a clapping rhythm, it was eventually nixed for sounding too much like a commercial. Ball said the hand-clapping also seemed like too "human" a sound when paired with the new graphic for Vista.

"There's nothing that's especially human about our new Windows animation," he said.

The short startup clip that was eventually chosen is meant to evoke the rhythm of the words "Win-dows Vis-ta!" and Ball hopes the sound will serve as a calling card for the operating system. It also consists of four chords — one for every color in the new Windows graphic that appears as the sound plays. It's no coincidence that it's also four seconds long.

There are a total of 45 Vista sounds that Microsoft has spent the last year and a half perfecting, including the dings you hear when you get a new e-mail, receive an error message, or log off your computer. Generally, these are more muted, less jarring variations of the prompts familiar to Windows XP users.

If it seems like overkill to go to all that trouble for a few seconds of sound, consider this: Microsoft estimates that the clips such as the e-mail alert will be played trillions of times in years to come. That's a lot of opportunity to annoy, offend — or, if the job is done right — please or appease computer users the world over.

One major concern was that the startup sound not grow grating after a time.

"You want a sound that people will love the first time they hear it, but it's a paradox to also say, 'Oh, and by the way, we need people to love it the 10th, or the 100th, or the 1,000th time they hear it,' " Ball said.

That's one reason he was glad to have 18 months to choose the clips.

"We had time to live with the music," Ball said.

Still, for all the time Ball has spent on the sounds, he says one measure of success would be if people noticed them very little, if at all.

Ball is the first to admit that the percussive beeps in past Windows versions could be jarring enough to bother nearby workers or interrupt others in a meeting. With the number of intrusive sounds from cell phones, handheld devices and other gadgets increasing, that's something Ball and his colleagues were keen to avoid with Vista.

"We want you to know they're there, and you would miss them if they were gone, but we would like them to be just barely noticeable, almost like they are part of the environment or part of your wallpaper," he said.