It's a concept that's so familiar to fans of The Philadelphia Orchestra it seems to need no explanation: the Philadelphia Sound. Born under the legendary Leopold Stokowski, burnished under the equally legendary Eugene Ormandy, the Sound has been part of the orchestral landscape for generations, acknowledged and enjoyed in Philadelphia and in concert halls literally around the globe.

The Philadelphia Sound is one of the main themes running through the 2015-16 season, a celebration of over 100 years of unique Philadelphia music-making, exploring masterworks given premieres, and therefore influential interpretations, by the Fabulous Philadelphians.

But what, really, is the Philadelphia Sound?

Some who create the sound today reach for similes:

"I'm a real foodie and wine lover, and I can only describe it as one describes great wine or great chocolate ... because you can't quantify it."

-David Kim, Concertmaster

"We use a lot more bow to make a fuller sound: a rich, fuller sound. There's a lot more warmth and robustness to the sound."

-Hai-Ye Ni, Principal Cello

And yet one of the Orchestra's most seasoned string players is full of praise for his woodwind colleagues:

"Richard Woodhams, Jeffrey Khaner, Ricardo Morales, Daniel Matsukawa: "They are first rate. ... They really are the center of the sound."

-Herbert Light, 55-year violin veteran

In addition, an often-heard remark is that the Sound was born in the Academy of Music, where the acoustics forced the musicians to dig deep and play their hearts out.

Yannick N_zet-S_guin was entranced by the Sound from his earliest guest-conducting stints. "At first I could hear it in some lines and phrases, and then in some entire sections of pieces. I felt, OK, I've turned the switch on something. Now it's my goal to try and put the switch on for the full concert!"

Reading about the history of the Philadelphia Sound left Yannick with the impression it was about power and precision. "But now, 100 or so years later, precision is something that many orchestras achieve; and we've become accustomed to powerful orchestras as well. Yet, this sound is special, so it means there's more to it than the two adjectives."

Yannick says the overwhelming impression he got the first time he conducted the Philadelphians was generosity. "That's different from power. It's not about being loud; it's about the loudness of the resonating soul."

He hastens to add that without discipline all those resonating souls on stage wouldn't mean anything. "The beauty is, this orchestra has extraordinary discipline as well. It's a combination of virtuosity and the lack of the feeling of hierarchy you get in so many other orchestras. Here, the last stand of the strings will give as much as the first stand, and so on throughout the sections."

Since arriving as music director, N_zet-S_guin says, "I've been inspired by listening to a lot of Stokowski recordings. We associate him with something big, a bold sound, but it's actually extraordinarily together and precise. You can't achieve clarity of a score if people aren't perfectly together, so I've been focusing on that clarity within the richness of the sound."

He's also trying to take the Sound and apply it to more of the repertory than it has traditionally been associated with, such as the big Romantic pieces by Tchaikovsky or Rachmaninoff. "Why not try to define that Philadelphia Sound in Haydn, Mozart, or Bach? What is that sound in contemporary composers? This is an endless thing to develop of course!"

In practical terms, how does he carry out his custodial responsibilities to the Sound?

Selecting the repertoire is crucial. "There should be a balance so we have occasions to go back to the conception of our Sound; where I can actually work on making sure that this is really how we nurture it, how we keep it alive, yet balanced with the new repertoire."

What about rehearsing? "I've never said 'Oh, this is not our sound.' What I can say, sometimes, even in working on well-known pieces, is 'you know, I don't think this is really us, or the way we can play it.' It's my role sometimes to just make people think back, or think anew and fresh about it.

"But I think that's more of a nonverbal thing, allowing that generosity to happen. That happens in rehearsal without me having to say 'please play generously!' Some orchestras would need that; we don't, which is great.

What if the Philadelphia Sound was somehow put in a time capsule, and dug up a century from now. Would it still be recognizable?

"Let me answer this way. When I listen to all of my predecessors' recordings, I do recognize the sound. Of course it's not only one sound: When we play Beethoven we shouldn't sound like Wagner; in the 1920s it shouldn't sound precisely the same as today. Also it's not the same musicians; even if there's a continuity, the individual musicians will have their personalities. Therefore it should change. However, I do believe that we as conductors also have the responsibility of keeping alive the specific colors of each ensemble.

"It's up to the conductors to listen as much as they give, in order to keep those alive. That is especially true when you're music director, but it's also true when you're guest conducting. So I do hope that the strength of the offering of this Orchestra is so seductive and so strong and imposing that if a guest conductor is shaping it, he or she lets it happen, too. I hope the same also for generations to come, and that in a hundred years we will recognize the Philadelphia Sound.

"I don't consider myself as a revolutionary or someone who tries to just break everything and start over. That would be pretentious and I don't believe it's my place. For me, there's a lot of listening and caring. This is only my little contribution in a certain period of time to something that's much bigger. So I approach it with respect ... but also with the conviction that I can bring my two-cents' worth!"