by Matthew Raley [youtube=http://www.youtube.com/watch?v=5xvwPMuCZEU]
For me, one of the transporting possibilities of chamber music is blending sounds. In a string quartet, such as we have here, each instrument can ride the tone qualities of the others, creating a corporate resonance.
Blend is not automatic. The Hagen Quartet uses a number of skills to produce it. Each player's intonation is not merely correct, but is tempered to the harmonic situation of each note. Also, the players use the blossoming of tone in their instruments to craft subtleties and climaxes together.
I particularly noticed their use of vibrato. It is not continuous. These players have forged a unity about when to use it and when to let notes speak for themselves.
All of these practices create the vibrations amongst the instruments that constitute blend. This is a marvelous performance of a gorgeous piece.