CARL PHILIPP Emanuel Bach (1714-1788), the most important of the several creative sons of the great Johann Sebastian, was far more renowned than his father in his own time, but has been rather under-acknowledged in ours. No less a figure than Joseph Haydn acknowledged him as the greatest single influence in his own work, and, significantly, it was Emanuel's keyboard music that first excited Haydn.

When we hear Emanuel's music today, it is usually orchestral material--his extraordinary little symphonies and his concertos for various instruments. His chamber music is performed occasionally, and even a choral work or two. The keyboard music, which the composer himself identified as the most personal segment of his catalogue, has also been the most neglected.

The first recording of Emanuel's entire collection of 18 keyboard Fantasias, played by Evelyn Garvey (Spectrum SR-146; cassette SC-246), is as welcome as it is overdue. Garvey's splendid performances are in fact doubly welcome for being played on the sort of instrument for which this music was written, a Philip Belt copy of the 1786 Anton Walther fortepiano preserved in the Mozart house in Salzburg.

It was the last of these 18 Fantasias that was specifically titled by the composer "C.P.E. Bach's Innermost Feelings." It is a brooding, probing piece in F-sharp minor, worthy to stand beside the great C minor Fantasy of Mozart and almost "pre-echoing" here and there the Funeral March in Beethoven's "Eroica" Symphony. At just under 12 minutes' playing time, it is also the longest of Emanuel's Fantasias, five of which are so pithy they run from only 16 to 49 seconds.

Not one of the 18 works, from the longest to the shortest, is less than fascinating. Among them are passages of the most forward-looking romantic expressionism and others recalling the keyboard style of Father Sebastian--often in quirky and totally unexpected juxtaposition to one another.

Garvey seems to be thoroughly inside this music, and the advantage of the fortepiano itself can hardly be exaggerated. In a comprehensive annotation almost as valuable as the fine performances themselves to anyone approaching this music for the first time, Garvey's University of Maryland faculty colleague E. Eugene Helm points out that, while some of the earlier pieces might be played on a harpsichord or clavichord, this is "the instrument specified by the composer for his most important fantasias, those composed between 1782 and 1787."

Helm calls our attention in particular to the instrument's advantage in negotiating the ornaments in these works--"trills, turns, mordents, etc. These quick and intricate little nests of notes, much favored by C.P.E. Bach, are nearly indigestible on the modern piano . . . yet are made pellucid by the light action of Philip Belt's fortepiano."

The music, the performance, and the instrument do add up to "a revelation," just as Helm claims, and his own contribution is quite invaluable as clarification of just what is being revealed. The recording itself is first-rate, the surfaces silent, and the offering of so important and thoroughly well-executed a production at so low a price should leave no one with much of an excuse for depriving himself of this experience.