For connoisseurs, the most impressive sound on records does not occur in the great, galumphing finale of the "William Teil Overture" or "The Pines of Rome" or any other big orchestral showpiece. It lies at another extreme - a solitary oboe, for example, with all its subtle, woody overtones captured fully and well-rounded in their unique contours, standing alone without the slightest trace of distortion against a background of pure silence. It is more impressive in the way a person who speaks softly, reasonable, surpasses one who screams and pounds on the table. Understatement is part of the effect, but total accuracy, freedom from distotion, is equally important.

I am listening to that kind of sound as I write. The music is relatively unfamiliar - the 1957 Duo for oboe and bassoon of Heitor Villa-Lobos, an exquisite modern tribute to the spirit of Johann Sebastian Bach. It is beautiful music, though perhaps a bit severe and abstract for middle-of-the-road tastes. The sound is, I think, the finest I have ever heard from a commercially distributed recording.

It is coming from an open-reel tape (MHS C 3187) manufactured and distributed by Barclay-Croker (11 Broadway, New York 10004) from a master tape made by the Musical Heritage Society. And its existence is a heartening sign that tape lives - open-reel tape, traveling at 7 1/2 inches per second and improved with all the new technology (low-noise oxides and the Dolby noise-reduction system) developed to make the smaller, slower and generally more problematic cassette format an acceptable high-fidelity medium. When this kind of tape is handled with care, nothing in the world produces better sound. Barclay-Crocker is handling it with care.

For nearly two years, it has been impossible for those who prefer to hear their music on open-reel tape to buy any new recordings in that format. The big record companies lost interest in what had always been a rather small, fussy connoisseur's market; it was easier and more profitable to push disces, which can be mass produced by a stamping machine like a giant cookie-cutter. When Ampex, the last major source of open-reel tapes, threw in the towel, Braday Crooker, a small company specializing in the mail-order distribution of tapes, faced the prospect of going out of business and decided instead to start making its own.

The first shipment of seven tapes, all drawn from the extensive, connoisseur-oriented Musincal Heritage catalog, is only the beginning; other releases are planned from recordings by Vanguard, Desmar and Unicorn as well as Musical Heritage (a tentative list can be obtained by writing to Barclay-Croker). Another company, Stereotape, is planning to issure recordings by London, RCA and Deutsche Granmophon, but has not yet begun distribution.

Once in a while, on some of the tapes formerly issued by the big companies, you could hear a perfection of sound comparable to what is audible on these tapes, but even the best older tapes in my collection havemarginally more hiss. Barclay-Crokerts sound is better partly because of more advanced technology but primarily because more care is being taken in production methods and quality-control.

Barclay-Crocker has taken a calculated risk, I think, by addressing this first release to a minority within a minority - open-reel tape devotees who are also chamber-music devotees, and not the "top-40" chamber music like the "Trout" Quintet or Tchaikovsky's "Andante Cantabile" but undservedly obscure music for woodwinds by Poulenc, Villa-Lobos, Saint-Saens and Glinka, piano music of Sibelius and organ music of Brahms. Part of the reason, no doubt, is that they know they are dealing with a special kind of music-lover, and another part may well be that the spectacular quality of sound on these tapes, its pure transparency, is best shown through the delicate textures of chamber music.

The superiority of the sound comes througy, no matter what equipment one uses. I have played these tapes on a 12-year-old Sony that cost under $200 when it was new, on a 7-year-old Tanberg 9000-X and on a brand new Revox A-77, They sound bteter on the Revox than on the Sony, but on the Sont they sound better than most commerical tapes played on the Revox.

There are no "big names" among the performers (Stokowski, Ashkenazy, Mthta and others will come later, largely form Stereotape), but the performances here are as fine as the sound - musical rather than showy, in keeping with the style of the whole project.

The tapes are reasonably priced at $6.95 each. Lacking space to discuss proximately in my order of preference:

Poulenc: Sonata for Clarinet and Bassoon: Trio for Piano, Oboe and Bassoon. Villa-Lobos: Duo for Oboe and Bassoon; Fantaisie Concertante for Clarinet, Bassoon and Piano. Members of the Soni Ventorum Wind Quintet (MHS 3187).

Saint-Saens: Caprice on Danish and Russian Airs, Op. 79. Bassoon, Oboe and clarinet Sonatas. The Minneapolis Chamber Ensemble (MHS 3324).

Sibelius: Kylikki, Op. 12 David Rubinstein, pianist (MHS 1218).

Beethoven: Quartet in E-flat for Piano and Strings, Op. 16. Serenade in D, Op. 8, for String Trio. Cantilena Chamber players (MHS 1795).

Brahms: Organ Music. Haig Mardirosian, organ of the Church of St. Paul the Apostle, New York City (MHS 1751).

Glinka: Trio Pathetique in D Minor for Clarinet, Bassoon and Piano- Selected Piano Works. The New American Trio (MHS 1973).

Domenico puccini: Piano Concerto in b-flat. Viotti: Piano Concerto in G Minor.Eugene List, Piano- Austriam Tonkuenstler Orchestra, Zlatko Topolski cond.(MHS 0709).