Bach works his calculated magic once again.
So when we learn that the Concerto for keyboard No. 3 in D minor, BWV 974, is based on an oboe concerto composed by Alessandro Marcello, it seems most curious — Marcello was not the skilled, stylish, and innovative composer Vivaldi was, nor was he the nephew of Bach‘s employer, as was young Duke Johann Ernst. And the fact of the matter is that, though Marcello had a certain influence in Italian music circles, he was not really a particularly fine composer (he was as much mathematician as musician), and, unlike Vivaldi, cannot be said to have exerted any real influence on Bach. One is therefore tempted to speculate that Bach chose to transcribe the Marcello oboe concerto perhaps even just to test his own skill — with an inferior source, his adaptive acumen would have to be all the sharper. And as he was not at all averse to altering Vivaldi‘s music when making the transcriptions, imagine how much more willing he would be to edit, refine, and rewrite the music of a really second-rate composer!
The Marcello-Bach concerto is in the usual three movements of an Italian instrumental concerto. Here they are: 1. unmarked (Allegro assumed), 2. Adagio, 3. Presto. The shell of the first movement is very clearly Marcello’s work; but Bach is quick to thicken the lean, open textures of the original — at the center of the movement things grow very dense indeed, with imitative, hand-against-hand sixteenth notes building up to eight-voice chords. The Adagio has a limber solo line atop steady eighth notes, while the Presto finale is a 3/8 time romp in near-continuous sixteenth notes, and almost exclusively in two contrapuntal voices.