The tape cassette, which seemed good for little more than voice dictation when it first appeared, has been refined greatly over the last several years, so that now it is not only one of the most convenient and durable modes for enjoying misic at home (and in the car), but can begin to compete seriously with discs in terms of sound quality.

Indeed, when Advent introduced its "Process CR/70" series about five years ago, several of its offerings - Jascha Horenstein's Nielsen Fifth and Mahler First, Zdenek Kosler conducting Mozart's Prague Symphony and Dorak's Slavonic Dances - actually sounded better than the disc editions of the respective recordings. The Kosler material, and a good deal else in Advent's early releases, came from the catalogue of the Connoiseur Society, one of the most respected of the small independent companies - which now has gone into cassette production on its own with a new line representing a further breakthrough for this medium.

The "Connoisseur Society Laboratory Series," issued on the In Sync label, uses chromium dioxide tape and the Dolby "B" noise reduction system, as Advent does, but goes a bit farther. First of all, the duplicator masters are recorded at 15 inches per second (two to four times the speed normally used). Besides that, the Dolby encoder has been modified to by-pass the filter which otherwise cuts off frequencies above 16,000 Hz, so that the range is from 30 Hz to somewhere above 20,000. Finally, the "intermaster" step in the duplicating process has been eliminated, and this too is a factor in affecting the spaciousness and live quality of these superb cassettes.

In the two releases so far, a total of 16 cassettes, there are some recordings not yet offered on discs, as well as transfers from some of Connoisseur's most successful disc releases. In the former category are four cassettes on which Jean-Phillippe Collard gives powerful and poetic performances of the four Rachmaninoff piano concertos and the Rhapsody on a Theme of Paganini, with the Orchestre du Capitole de Toulouse under Michel Plasson (C 4001 through C 4004, with solo pieces by Rachmaninoff filling out the cassettes of Concertos 2 and 4), and a handsome Bartok recital by another young Frenchman, Michel Beroff (C 4006).

There is also a stunning Honegger collection with the Orchestre National de l'ORTF under the late Jean Martinon, whose readings of Pacific 231, the Pastorale d'ete and Rugby breathe new life into those pieces, and whose presentation of the Christmas Cantata confirms that work's place as the most endearing part of Honegger's legacy (C 4011).

Among the transfers from discs are two more orchestral items - Roussel's Psalm 80 and Bacchus et Ariane Suite No. 2, conducted by Serge Baudo (C 4008), and the complete version, with chorus, of Franck's Psyche, conducted by Paul Strauss (C 4009), both of which sound every bit sumptuous as they do on discs - and two from the splendid series violinist Wanda Wilkomirska has been recording for Connoisseur. In the three Delius sonatas with pianist David Garvey (C 4012) and the pairing of the Franck Sonata and Syzmanowski's Mythes, with Antonio Barbosa at the keyboard (C 4010), Wilkomirska is at her glorious best, and the absolutely silent background permits the intimacy as well as the brilliance of her playing to make the fullest impact, I hope her Grieg and Ravel sonatas with Barbosa will turn up in this format soon.

Another exceptionally impressive transfer, in terms of both performance and sound, is Lionel Rogg's recital of Liszt's organ works (C 4005). Of somewhat earlier vintage, but still dazzling, are Ivan Moravec's Chopin assortment (C 4007) and his Debussy/Ravel program (C 4013). Beroff and Collard together in Brahms' Hungarian Dances are irresistible (C 4014), and there are two more two-pianist cassettes, with Veri and Jamanis offering Gershwin originals and transcriptions (C 4015, 4016).

The In Sync line is not cheap - the list price is $10.98 - but the quality is really incomparable, and there is a generous "no fault" replacement policy: if one of these cassettes is damaged in use, In Sync will replace it, no questions asked, for $2.