There has been a quiet revolution in the performance of baroque music the past few years. Through the '50's and early '60's, as mountains of eighteenth-century manuscripts were unearthed, audiences were exposed to essentially romantic interpretations of old music (as pre-1800 composition is often called). More recently scholarly work in the difficult field of performance practice has made possible the production of a sound closer to the original medium than ever before.

The new Telefunken recordings (SA WT 9059-10) of the J.S. Bach orchestral suites are a superb example of how musicological scholarship has radically transformed performance. Played by the Concentus Musicus of Vienna, the suites are led by Nikolaus Harnoncourt, an excellent viola da gambist and brilliant musicologist.

The most striking difference between the Concentus Musicus and other orchestras is the quality of sound: this group is completely different. The reason is the instruments: all are originals or reconstructions of seventeenth and eighteenth-century instruments. The strings have a far brighter sound, richer in harmonics than their modern counterparts. The string choir resembles a group of soloists rather than the modern symphony's big, anonymous cushion of sound. The woodwinds are changed from the way we know them: the oboes and bassoons, like the strings, are sharper and brighter; the flute is much softer. The brass is an entirely different world. The baroque trumpet, producing notes only by the natural overtone series without the aid of valves, has a brilliant, searing sound. All in all, the baroque orchestra is a gathering of strikingly individual voices, quite the opposite of the contemporary orchestra.

Coupled with the actual instrumentation, Harnoncourt's group has devoted great energy to proper embellishments of the parts and such details as correct bowing technique for accurate phrasing. The effect is startling. When the initial awe of hearing the new sound is overcome, more and more the conviction sinks in that this is what the baroque sound must have been like. Harnoncourt refuses to cut the length of the suites: he does not omit a single repeated section. This is an important consideration in the overtures, the first and largest movement of each suite. Standard procedure is to play the opening slow section twice, but then to play the fugato passage and closing lento only once, omitting the final repeat. By observing the repeat, the exact proportion of overture to the following dances is restored.

The sensitivity and flexibility of the interpretation is astounding. The two bourrees of Suite No. 2 are usually done at one tempo. Harnoncourt easily could have selected what he considered the optimum tempo for a bourree and simply plunged through both of them with metronomical precision. Instead, he slows down the second bourree, allowing the solo flute to come out--and then returns to the opening tempo in the da capo. In the extensive program notes that come with the two discs, Harnoncourt explains this by characterizing one bouree as stuermische and the other as delikate; and he plays them accordingly.

The Second Suite, essentially a concerto for baroque flute, is the masterpiece of the four. Leopold Stastny, the soloist, is a phenomenal player: his pitch is dead accurate. He complements subtle shadings of tone and fine techniques with beautiful phrasing that never is broken in awkward moments for breathing. The supremely beautiful moment of the Suite is the Double of the Polonaise: the theme of the Polonaise appears in the bass (played as if a solo part by Harnoncourt himself) with an incredibly florid counterpoint in the flute part. The beauty and care taken by Harnoncourt in his accompaniment is outstanding. The usual fate of this section is to have a frantic virtuoso display by the flutist over a barely-audible figured bass.

The finale of the Second Suite, a Badinerie, is described as a "ready-composed encore" by Harnoncourt. The bounce in the string accompaniment is infectious. All of Bach's brilliant counterpoint shine through because of the bright string sound. No wonder, then, that the Concentus Musicus used the Badinerie for their encore in last fall's Sanders Theatre concert.

The Third and Fourth Suites are notable for their employment of the baroque trumpet and baroque tympani (the latter, too, different from its contemporary). The Fourth Suite has three competing choirs (in best concertato style): the strings, oboes and bassoons, and trumpets and tympani. The concept of tympani acting as a bass instrument (as legitimate as bassoon, cello, or violone) is foreign to us; but the particular sound of these drums (partly from the use of ivory mallets without felt) gives them a much brighter tone that blends with the trumpets.

It would be unrealistic not to acknowledge the somewhat tarnished reputation of original-instrument recordings. It is not uncommon to find record-collectors who have been disgusted with records claiming authenticity that simply sound bad to them. There is truth to this: there are groups who have sought to escape charges of faulty musicianship through lame invocation of historical accuracy. The victims are innocent record-buyers. One friend of mine became so disgusted with original instruments (on an admittedly poor Fireworks recording) that he refuses to consider another purchase of the sort. The Concentus Musicus is the answer to this dilemma: they provide the technical perfection of modern instruments with the eighteenth-century sound.

But reason alone will never convince everybody. Many listeners cannot adapt to an orchestral sound not of the nineteenth century, no matter what the composition being played. It is for these people, the majority of the buying public (and of practicing professional musicians, for that matter) to whom the Argo release of the Bach orchestral suites is aimed. Neville Marriner leads the excellent Academy of St. Martin-in-the-Fields through their well-rehearsed paces.

The Argo (ARG ZRG687-8) issue is simply a conservative product, joining the other seven traditional recordings of the Suites listed in Schwann's. It says practically nothing new. There is passing obeisance to research, evident in the over-dotted rhythms of the overtures and in some imaginatively-ornamented solo passages. The flute and harpsichord playing, by William Bennett and Thurston Dart respectively, is first-rate. But this is just another rendition with tempos quicker than usual. If you are wearing out your old Herman Scherchen or Karl Ristenpart' discs, then this would be a good replacement. But...

A whole new world awaits you with the Harnoncourt recordings. It could easily be shocking. Though having played in the St. Matthew Passion here last spring, still I thought I had put on the wrong record when first hearing the Concentus Musicus recording of that piece. Baroque music is not musty, dense, or unreachable; it is powerful and active. The Concentus Musicus has virtually transcended their time in emotional and intellectual appreciation of the music of a different age.