"This is for anyone who's ever wondered what it would be like to have Frank Sinatra singing in your face. Every so often he'll pop a syllable and you get the feeling of a spray of saliva hitting you, it's so . . . real!"

That's Gary Giorgi, vice president at Mobile Fidelity Sound Lab, and he's talking about the ultimate status symbol for the legions of Sinatra fans here and abroad: exquisite pressings of Ol' Blue Eyes singing at the top of his career.

For audiophiles whose coffee tables became a little unbalanced under the weight of last year's 14-record boxed set "The Beatles/The Collection," equilibrium is at hand: October will bring an even heftier 16-record Sinatra box featuring almost all of his work for Capitol Records in the '50s.

The set, simply titled "Sinatra," will be in a heavy case sheathed in silver fabric and will list for $350, a limited-edition audio lithograph representing much of the best work in Sinatra's career, including such classic albums as "Songs for Swinging Lovers," "Come Fly With Me," "Only the Lonely" and "All the Way."

Mobile Fidelity, the California company that launched the half-speed audiophile market in 1978, is betting that Sinatra fans are as rabid as the 20,000 Beatles fans who shelled out $325 apiece for "The Collection"; now effectively sold out, the Beatles set is expected to be worth $1,000 in the collector's market within the year.

Herb Belkin, Mobile Fidelity's president and former head of A&R at Capitol, says the Sinatra fan "is likely to be willing to spend big bucks. He or she is older, more affluent and, in a sense, as zealous a fan as you'll find anywhere."

Half-speed mastering provides highly enhanced sonic detail--increased dynamic range, a cleaner high end, a fuller low end, better response all across the spectrum. Mobile Fidelity's Giorgi says the company expects sales of 25,000 on the new set.

Mobile Fidelity, which has leased about 150 studio masters for albums since 1978, developed the process in which original tapes are mastered at half speed to bring out the full aural nuances; the records are also pressed in carefully monitored and limited editions on the world's highest quality vinyl. Individual records usually sell for $15 to $17 and, in the case of the Beatles sets, seem to flit between being instant collector's items and expensive audiophile status symbols.

"We did Sinatra's 'Nice and Easy' a few years ago, basically as a trial balloon," says Belkin. "We knew from 'Abbey Road,' 'Magical Mystery Tour' and the 'White Album' that the people we market our product to obviously loved the Beatles. Sinatra was an idea that we wanted to test before we went ahead with it." The response was strong and Belkin and his forces started thinking in terms of a boxed set: Work on it began last November, right after the Beatles "Collection" came out.

While a dozen of the "Sinatra" albums are in stereo, four are not. Says Belkin, "When we went through the Capitol catalogue, we came upon some incredibly well-preserved master tapes that were mono. But when we tested them half-speed, you couldn't tell they were mono--they had such depth and separation. They were better than anything we did with the Beatles."

"Sinatra's" four records will be the first audiophile monos to be released. Belkin says it was Giorgi who convinced him that "we could get out of mono the same kind of dynamism that is so easily gotten out of stereo. I knew the people who produced and engineered those recordings, and they were geniuses at miking techniques. In the early days, Capitol was really ahead of everybody in engineering and the building of studios. The rooms these records were recorded in, the engineering skill all had a role, as well as Sinatra himself. And what you get is absolutely sparkling recordings."

"I was not really surprised," says the company's chief engineer, Jack Hunt, "because in those days engineers were really engineers: Everybody had to make a decision on the spot and they went with the sound. They used much simpler microphone techniques and they didn't let all the electronics get in the way of the music. The clarity and recording quality that was possible in those days was really phenomenal and certainly made my job a lot easier."

"You'd be hard pressed to identify them as being monaural," says Giorgi of the four mono albums. "Sinatra always insisted on being in the studio with the orchestra and he would always have them in front of an invited audience--and all of those elements jelled in these recordings. There's an element of space, of depth, of detail, that one ordinarily associates with stereo."

Sinatra actually recorded 22 records for Capitol before ending a stormy relationship in 1959 and leaving to form his own company, Reprise. Mobile Fidelity will release 16 discs. It dropped three soundtracks ("High Society," "Pal Joey" and "Can-Can") because there just wasn't enough Sinatra, a Christmas collection (which will be released separately) and several other albums whose quality has been affected by storage or deterioration.

The market is admittedly small: Belkin estimates the "universe of true audiophiles" is 50,000 to 75,000, though some albums have sold their maximum pressings of 200,000. It's hard, he says, to get a grasp of that audience's demographics, "except through our mistakes. Generally it's an older, somewhat more upscale and better-educated music fan. There's a logic to all that, because it's difficult for anyone who's not willing to invest a substantial amount of money in playback equipment or learn what to do with it to fit that profile. To talk about the 'dynamic nature' of the audiophile market is an understatement--it zoomed, bombed and is, I think, in the process of being resurrected in what one would consider record time."

Pink Floyd's "Dark Side of the Moon," whose traditional stereo version is still on the charts after 482 weeks, was the first major record presented to consumers in the audiophile medium. "It was outrageous and caused 12 companies to go into the half-speed business," Belkin says. "None of them is in the business any more."

The Mobile Fidelity-Capitol connection extends from Pink Floyd through the Beatles through Sinatra. "They were the first to realize money could be made by participating in the audiophile market," says Belkin. "They have been very cooperative and most adaptable to the non-threat nature of what we do to what they do."

The Beatles set, and now the Sinatra, indicate a new direction for Mobile Fidelity. "When we began I'd have been thrilled if we'd sold 5,000, because nobody'd ever done anything like it," Belkin insists. "We knew what it was, but we didn't know how dedicated people would be when it came to that big a pocketbook dip. I see our company and what we do changing as a result of getting into this kind of a business, with much more legitimately limited-edition things, and also smaller sets."

Mobile Fidelity will get into opera in November when it releases the London recording of Luciano Pavarotti's "La Bohe me," on supervinyl and mastered at half speed; Placido Domingo's "Carmen" is to follow soon after.