There is an art to coaching an ensemble, says violinist Barry Shiffman, who left the St. Lawrence String Quartet last year to become director of music for the Banff Centre in Canada. “What’s great about Paul,” he says, “is the breadth of his experience. String quartet is the art of conversation, and Paul listens to everyone. To coach a quartet, you have to be a bit of a psychiatrist. You take on a role much greater than finding the right tempo in a Beethoven quartet. You help them learn how to live the life.”

Liz Freivogel agrees.

“He talks to us about practical things like how to build repertoire, when to enter competitions, how to plan a concert tour and resolve differences in the quartet,” she says. “In general, I don’t think conservatories focus enough on that stuff.”

This year, the Parker Quartet has the honor of holding the quartet residency position, which entitles its members to free tuition, a stipend, and two coaching sessions a week from Katz, plus one from another member of NEC’s chamber music faculty, either Martha Strongin Katz, Donald Weilerstein, or Laurence Lesser. Since the program was established in 2000, it has launched the Kuss, Biava, and Jupiter quartets, all of which have won major competitions, secured professional management, and made recordings.

Sometimes Katz sits in with his cello during a coaching session. “When he plays in the quartet,” says violinist Karen Kim of the Parker Quartet, “we can feel his phrasing in a way that’s hard to resist. You feel how strongly he puts forth his ideas, how much goes into being a good quartet player.”

Always, Katz considers sound quality.

“I like to think of myself as a colorist,” he says, “and I am preoccupied by what I can paint inside a single sound. For a sound to stay alive, something interesting should happen within it.”

When he works with the Ariel Quartet, a young group from Israel studying at NEC, he hears “dirt” in some of their passagework. “That’s just unacceptable, the quality of those four notes,” he says. “Play your instruments extremely neatly. Practice it slowly and warm up the sound.”

They do.

“That’s beautiful,” Katz says, smiling with deep satisfaction. A few days later, the Ariel Quartet wins the 2006 Fischoff National Chamber Music Competition.

So sensitive is Katz to sound quality that it affects his sense of pitch. He has perfect pitch, but only with respect to certain instruments.

“If you play me a note on a cello,” he says, “I can tell you what it is. On the viola, I can guess right about 75 percent of the time, and on the violin a little less often than that. On the French horn, I couldn’t do it at all.”