After the terrorist attacks of Sept. 11, jazz musicians wasted no time getting back to business.

Within the week, pianist Ramsey Lewis and vocalist Nancy Wilson returned to a Chicago recording studio to cut their latest release, "Meant to Be"; Chicago singer Kurt Elling went ahead with an already scheduled concert at the Park West, speaking to the audience expansively about the importance of returning to a semblance of normal life; and Wynton Marsalis brought a small army -- including the Lincoln Center Jazz Orchestra, the Los Angeles Philharmonic and a gospel choir -- into a West Coast studio to record his epic work, "All Rise."

Following that initial rush of activity, however, jazz musicians found that their world had changed, though they're not sure they can attribute the shifts to Sept. 11.

The world they live in, in other words, is so complex and evolving so quickly that it's difficult to sort out causes and effects, even if Sept. 11 may be at the root of some of the developments.

"I'd say everything is down, everything is less by about 20 percent than it used to be -- less work, less recordings, less coverage," says prominent New York jazz publicist Helene Greece.

"We're still busy, very busy, but not quite as busy as we were the year before.

"But is that just the economy or Sept. 11 or both?"

Neither Greece nor other jazz professionals, promoters and musicians can answer that question definitively. They're keenly aware that there's less business and more turbulence in the world of jazz performance and recording, but they hasten to note that Sept. 11 and the recession are not the only driving forces.

"Look at what's happening in the music business in general," says Michael Friedman, owner of Chicago-based Premonition Records, a widely admired independent jazz label.

"Technology has changed the record industry, because it's so easy to download music or burn CDs and give copies to your friends, and that's cutting in to how we sell records.

"Then you have the airline industry in trouble, the decline of tourism, the corporate scandals -- that's all going to affect the economy and, therefore, affect the world of jazz.

"Some of it has to do with Sept. 11, some of it doesn't."

As far as the art, rather than the business, of jazz, is concerned, however, no major artist is known to have conceived a piece explicitly in response to Sept. 11, as others have done in rock (Bruce Springsteen's "The Rising") and classical music (Ned Rorem's "Aftermath").

Yet the disaster of Sept. 11 still haunts their performances, says Chicago jazz innovator Kahil El'Zabar.

"The responses we've been getting from audiences says to me that Sept. 11 is still very much in the air," and on the news says El'Zabar.

"Listeners are realizing, as they haven't in a long time, the healing power of music, and they're responding accordingly.

"For the musicians, the past year has been a time of reflection, and Sept. 11 informs our performances -- whether we know it or not."