I was just reading about the Estonian conductor, Kristjan Järvi, yet another baton-wielding member of that intensely musical family. In a recent piece for The Australian, Matthew Westwood writes of Järvi’s crusade to bring more improvisation to the concert hall. "It is really important to make the performers feel that they have freedom, that they can express music rather than just play the notes," Järvi says.
Järvi’s spot on when he points out that this was expected of musicians from the medieval to the classical eras. One look at a Perotin motet or the figured bass of a Bach sonata will tell you that there are lots of blanks to fill in.
And in a sense, as Järvi suggests, realizing a figured bass IS something like playing jazz. The notes on the page are a skeleton; it’s up to the performer to give it flesh. This is also true, though to a lesser degree, in the other parts of Baroque music. It’s the performers’ prerogative (or obligation) to stamp them with a bit of style.
The question of just what that style should be is one that the historically informed performance movement (HIP - read about it here and here) has tried to answer. One of HIP’s elements is an effort to teach performers the interpretive language of early music, so they naturally play it the way a musician of the period would have. Comparing this with jazz practices will be left as an exercise for the reader. 
But Järvi doesn’t seem to be that interested in Baroque and Classical-period music. Rather, he seems keen to let folk influences and improvisatory elements have sway in more recent works. "Whether it’s Sibelius, the Nordic composers or Piazzolla and Ginastera, I really love the national flavour when it comes out in the music of serious orchestral composers," he says.
I may be missing something, but it seems to me that this is at least as much the conductor’s responsibility as the orchestra members’. There’s a good reason that collectors treasure Karel Ancerl’s 1963 reading of Smetana’s Ma Vlast, for example. How much of that is Ancerl’s view and how much his players’? You could make a pretty good case, I think, that performers’ personal interpretation is more appropriate in solo and chamber music than it is in orchestral music.
What’s more, national flavor isn’t static. Folk and popular music performing traditions are contantly evolving. If the musicians apply a Finnish "national flavour" to a Sibelius symphony, should it be the “national flavour” of Sibelius’s time, or of ours?
Finally, how far should we take this bus? Will future generations react to Järvi’s "tweaking" of the standard repertoire the way our generation has reacted to the interpretive excesses of the early 20th century performers and conductors?
Stay tuned. It’ll be intriguing to see Järvi run with this ball.
It is difficult for a modern musician, trained to play what is before his eyes, to realize that the author [composer] did not intend his text [notes] to be followed.
