The fortepiano, an instrument midway between the harpsicharod and the modern concert grand both in sound and historic evolution, has not received the kind of attention from performers and recording companies that has been lavished on the recorder, harpsichord, viola da gamba and other archaic instruments. The reason, I suppose, is that it is usually considered a sort of rudimentary or imperfect Steinway - a bit clangorous in tone, with fewer notes and more restricted dynamics and lacking the homogeneity of voicing from deep bass to top treble that is found in the modern instruments.

All quiet true, but the fact remains that this is the intrument for which the great classical composers wrote their keyboard masterpieces, and if we want to hear it at least occasionally on a period instruments. In addition, the fortepiano does have different charm from that of the modern piano (which in many ways is actually a percussion instrument): a transparency of tone, a sharp contrast between the treble and bass registers, a lightness of touch and a quickness of action that suit the style of Mozart, Haydn and early Beethoven much more closely than today's pinos.

Interest in the fortepiano has been reviving recently, and we may expect in the future that it will become as regular a part of the music scene as the harpischord is today. The beginning of that trend can already be seen - for example, on two new, superbly recorded and well-performed cassettes, titled "The Viennese Fortepiano" (Dvent cassettes E1056 and E1058) and performed by pianist (in this case for tepianist) Malcolm Bilson.

The program is ideally chosen to show the virtues of the several old instruments (or new ones modeled on the old) played by Bilson: Vol. I offers two Mozart rondos and the two beethoven sonatas of Opus 27 (the second of which, for some reason, has been nicknamed "Moonlight.") In Vol. II, we are treateed to two Haydn sonatas (Nos. 40 and 52 in the Hoboken listings) and Mozart's Sonata in D, K. 311.

The quickest reference point for the difference between the fortepiano and the pianoforte is the familiar "Moonlight" Sonata, particularly the thundering finale (the gentle opening bars are not too different).It is also the hardest test for the fortepiano, since the Sonata is so well-known and loved in less authentic performances. Sometimes it sounds almost like a two-key-board performance - piano for the right hand, harpsichord for the left - and never does it sound like any other performance you have heard.

You may, of course, prefer the modern instrument - it certainly whips up the adrenline more effectively - and you may choose to believe that Beethoven dreamed of a Steinway when he wrote this music. But the fact remains that this is the kind of instrument he played it on and the differences are striking and significant. For all the other music on these cassettes, the appropriateness of the fortepiano seems beyond question. The clarity and light-flavored lyricism of the music interlock seamlessly with the qualities of the instrument; the notes flow with a crisp articulation that comes naturally at thsi keybaord, though players trained on modern pianos have to work hard to develop it on that instrument.

It is less likely that we will see a large-scale revival of the violin in the form it had in the 17th and 18th centries. The need is not felt; after all, we can go to live concerts fairly often, or put on a record any time, and hear a virtuoso playing Bach on a Stradivarius or Guarneri taht was built during the composer's lifetime. The simple fact, howere, is that virtually all of the violins in existance that date from the 17th or 18th century have been "improved" by modern craftsmen - the bridges raised, the necks lengthened, chin-rests added and sometimes the structure reinforced so they can accomodate brilliant, modern metal strings under high tension rather tahtn the warmer-toned gut strings of the past. The difference between old and new in violin sound is striking on several current records, two of which feature Bilson at the fortepiano with violinist Sonya Monosoff, a respected specialist in 18th-century music. On Pleiades P 104, they play three Mozart sonata (K. 304, 376 and 380) on a Stradivari that has been restored to its original form and a fortepiano built in the 1790s by Johann Schmidt, who was a friend of Mozart's father. On Titanic Ti-12, they are joined by cellist John Hsu in three Hayn trios (Nos. 19, 27 and 29). Both records attempt to reconstruct the sound of the music as close as possible to the original; besides being sensitively performed they come as something of revelation to most listeners. The pitch is lower than the modern standard, and the gut strings have a warm, transparent tone taht you simply can't hear with the modern instrument.

Finally, an even more striking 18th century instrument is played by violinist Carol Lieberman on a record from a very small company in Massachusetts (AFKA Records, P.O. Box 22, Wilmington, MA 01887, SK-299). The program (with harpsichordist mark Kroll) includes three moderately interesting soantas by the virtually unknown Simon le Duc and one very good one by K.P.E. Bach. Lieberman's violin is a unique listening experience for the connoisseur.