3. Watching. Even when they're just talking, they watch each other.

"You can feel a moment very strongly, but someone else in the group can feel it differently. There's always more than one beautiful way to play music. So you've got to be flexible . . . "

Playing with a quartet, you're juggling so many things. You can get too loud, too fast, too intense. Even as you put all the skill of 30 years into your playing, you are forever thinking about the total sound.

You make a vibrato on a violin by ever so slightly wiggling the finger that is pressing down on the string. In a quartet you try to match your vibratos, both in speed and aplitude, for if one vibrato is dramatically broad and another is tight and narrow, something is lost in the music.

"We use the composer's markings as a point of departure. But how and where we want to depart is the question. We're trying to get the general feeling of the movement across, we have to agree on that. The over-all feeling. But our concept of this can change too when we play a piece 30 or 100 times."

A curious note: The group knew some of Beethevon's 17 quartets intimately, some not at all. The new ones came easily; right away, they arrived at an interpretation they all liked. They suspect it had to do with their similiar musical backgrounds. But as for the familiar work, one member might have grown up with the Budapest Quartet's recording, another might have studied it at Juilliard or played it with another group. These were the hardest.

"We were starting from divergent viewpoints, strong influences from somewhere else in our lives. It was a struggle, wrestling it out, working it through. And those are the ones that turned out to be our most successful. The audiences like them best. This is what makes us feel it's all worthwhile."

When they're tense, not getting along well, their responsiveness to one another changes. Sometime they go onstage after a bad rehearsal, and they play without enjoyment, but there is no sign that this comes over to the audience. Sometimes they start off in a bad mood, and the beauty of the music lifts them out of it.

"A good audience can really set you up. We love New York. They concentrate. The silences are part of the music."

True, a sneeze or sudden cough can disturb the timing, wrech an entrance, but audiences also can bring the quartet together and focus it. Their antennae go out. "You know when you've reached 'em." There is this sense of a great presence out in the dark, with a mood of its own - did you ever go to a concert on the night of a blizzard? - and the players miss it in record sessions.

Yet in the studio, though they aren't projecting to live listeners, another thing happens: repeating and repeating, meamerized, they seem to be playing for themselves, and the music takes on an interior quality.