POSSIBLY the earliest of all digital recordings -- or, at least, of those released commercially -- was the one on the Mussorgsky/Ravel "Pictures at an Exhibition" made in 1972 by the Tokyo Metropolitan Symphony Orchestra under Louis Fremaux, which has been in circulation here the last few years on Denon OX-7072-ND. It is a more than respectable performance, very brilliantly recorded, and well deserves the success it has enjoyed among audiophiles.

Since 1972, however, Denon has upgraded its digital hardware twice, and two of the finest American orchestras have made digital recordings of this work. First in 1978 came Lorin Maazel and the Cleveland Orchestra on Telarc DG-10042; now there is a new version by Sir Georg Solti and the Chicago Symphony on London LDR-10040 which really has to take top honors, both interpretively and sonically, among digital "Pictures."

Maazel had recorded the "Pictures" twice before in London. He has a fine feeling for the music and his Telarc recording is a blockbuster. All the emphasis on bigness in the recording itself, however, tends to get in the way of the music a bit.

Solti is a conductor we might have expected simply to pull out all the stops, unleash his great orchestra's incredible power and go for the most staggering effects, but his response is an extremely sympathetic one. What he offers is a sensitive realization in which each of the individual episodes is well characterized and everything is in splendid proportion. London/Decca, for its part, does not emphasize the drums or the brass or any segment of the orchestra, but preserves the natural balance -- and achieves some almost frightening realism in reproducing the live quality.

The filler is an imaginative one, too. Instead of the almost inevitable "Night on Bald Mountain" (offered by Maazel, among others) or "Bolero," side two is filled out with an unexpected Ravel encore, "Le Tombeau de Couperin." In this suite Solti may not show the remarkable affinity exhibited by Boulez, Ansermet or Karajan, but the superb playing of the Chicago winds and strings is a very considerable pleasure in its own right, and it is all pretty easy to like. The Dutch pressing is perfection itself; indeed, if there is any cause for complaint it can only be the ghastly cover art, and one really doesn't have to look at that.

Solti's Brahms symphonies with the same orchestra, issued as a set less than a year ago, are beginning to appear separately now. The first to be released on its own is the Fourth (London CS-7201) and it seems more impressive now than when heard with its companion works. It is a grand, mature, compassionate, and of course beautifully played, Fourth -- missing only that last degree of warmth and wit (the latter quality does figure in the third movement) that one does hear in Karajan's similarly proportioned latst recording of this work (Deutsche Grammophon 2531 134). I'm sure, though, that Solti has given us no finer performance of any of the standard-repertory symphonies since he began recording in Chicago, and I look forward to the independent reissue of his Brahms Second.

A reissue already to hand, and an exceptionally welcome one, is the RCA Gold Seal disc which restores to the catalogue Charles Munch's uniquely authoritative performances, with the Boston Symphony Orchestra, of the Sixth Symphonies of Walter Piston and Bohuslav Martinu, both of which were composed for that orchestra's 75th anniversary (AGLI-3794). This coupling originally appeared only monophonically, and did not stay around very long; this is its first stereo release and it does gain, if only slightly, in clarity and definition. A brand-new recording of the Martinu Sixth (originally titled "Fantasies symphoniques") by Vaclav Neumann and the Czech Philharmonic appeared only a few months ago, in Supraphon's complete Martinu cycle, coupled with the lesser-known but decidedly worthwhile Second (1410.2096). Munch's performance has a bit more electricity -- that sense of momentum and spontaneity he brought to his most dedicated undertakings -- and there is simply no other recording, still, of the Piston Sixth, which may well be the finest of all that composer's symphonies. All in all, a treasurable restoration.