With Night & Day, Chicago focuses on well-known tunes from the big band era, among them Duke Ellington's "Take the A Train" and "Sophisticated Lady," Glenn Miller's "In the Mood" and "Moonlight Serenade," Benny Goodman's "Goody Goody" and Cole Porter's "Night and Day." The group took those and six more big band classics (including, as might be expected, "Chicago," made a hit by Frank Sinatra more than three decades ago), and, in Pankow's words, "lobotomized" the songs by updating the arrangements and putting the band's own stamp on the songs to create a "Chicago-ized," contemporary interpretation of the tracks.

To put into perspective the sensitive nature of Chicago's tinkering with big band standards, Pankow, Chicago's trombonist, recalls the reaction that came when the group redid their 1970s hit "25 or 6 to 4" a few years ago.

"We did a remake of '25 or 6 to 4' and released that as single, and by God, we got more flak," Pankow says. "I mean, it was as if we spit on the cross. Program directors were sending us hate mail. 'How dare you bastardize a Chicago anthem?' And our response was, well, 'Hey, we created the original. If anybody has a right to do a remake, we do.' And they didn't want to hear it ... so you can imagine what a song that has been a classic for 50 years would generate had we bastardized it."

While critics and music fans will have the final say on whether Chicago updated or defiled the songs on Night & Day, Pankow and keyboard player/singer Lamm, not surprisingly, feel the band walked the fine line that separates interpretation from bastardization. "I think, in listening to the CD, it's apparent that we treated those songs with a lot of love and respect, but didn't fall into the trap of trying to recreate the original," Lamm says.

The big band project comes at a time when Chicago, according to Lamm, is trying to get back some of the spirit that marked the group when it first began in 1967. It also comes at a time when Chicago has left its longtime major label, Warner Bros., for a smaller independent label, Giant. The break came because Warner declined to release what would have been Chicago 22, a CD of up-tempo original songs with producer Peter Wolf.

"They not only didn't understand [the CD], they hated it," Pankow says. "They asked us to go back into the studio and do another. And we told them absolutely not. This is what we are. This is what we had to do. This is a band album. And we wound up parting company because it was beating a dead horse. Rather than shove this thing down their throats, we figured it would probably be best to have a mutual parting of the ways."

Lamm admits that the still-unreleased CD was a major departure from recent Chicago albums. But that's one of the reasons the band liked it. "In some cases it was experimental," Lamm says. "It was experimental for sure sonically.... It had a kind of more urban and world edge than you would imagine with Chicago, which I think is really what scared Warner Bros. I think they got scared more than anything else. And I think the quality of the songs is very, very high."

What Warner Bros. was undoubtedly hoping for from the band was the ballad sound that gave Chicago a long string of hit singles during the 1980s ("Hard to Say I'm Sorry," "Hard Habit to Break" and "You're the Inspiration," to name a few). Talk of that sound prompts mixed feelings from Pankow and Lamm.

"I think we were victimized by our own success," Pankow says. "I mean, radio heard Chicago in one way, and that is power ballads. And you know, no matter how great an up-tempo song [we did], they didn't want to hear it. On Chicago Twenty-1 we tried to minimize the availability of ballads for the radio program directors, just to increase our odds of having an ass-kicking song on the radio. But even if there was only one ballad on that record, that was the candidate for a single, because that was all they heard Chicago as being.

"So that became almost a wedge in the band, where it caused dissent and it caused a feeling of frustration, because no matter how hard we tried to be heard for the other side of what we are, it was of no avail. I mean, we're writing all this incredible music and only a small portion of it is being recognized by the people who make your career. And that was disgusting."

Even though seeing a project get shelved was frustrating -- both Lamm and Pankow say they think the Wolf-produced CD will be released in some form at a future date -- the process of making the record has helped shift the band's direction. "I think it was so positive," Lamm says. "I think that first getting into the studio and doing a courageous album like that was great for everybody, because even though the music business industry side of it didn't work out that time, the songs that everybody contributed were really good and really original and really fun to listen to."

That break of standard Chicago form made it easier for the band to then turn around and attempt something else out of the ordinary -- the big band album, which aside from being one of the few times Chicago has covered other performers' music, is also one of the handful of Chicago albums to not be numbered.

Surprisingly, Chicago's members -- Lamm, Pankow, Lee Loughnane (trumpet), Walt Parazaider (woodwinds), Bill Champlin (keyboards, guitar, vocals), Jason Scheff (bass, vocals), Tris Imboden (drums) and Keith Howland (guitar) -- had only a limited knowledge of big band music when work began on the project. This made the CD an educational process, says Pankow.

"I'll tell you, we learned a lot of respect for these [big band] guys," Pankow says. "I mean, before we really got into this stuff, we weren't any more of an expert than you or anybody in terms of this music, because obviously it was another generation. But when we listened to this stuff, we were totally taken aback by the musicality of it. When you take this stuff apart you are just amazed at the intricacies and the difficulty of this music that sounds so harmless."

On the tour that comes to The Woodlands Sunday, the group will be playing a mix of big band standards and standards of Chicago's own. Lamm and Pankow also hope that Chicago might be able to show longtime fans a band in rejuvenated form. "It takes some talking and doing to get everybody focused on one vision," Lamm says. For a while, Chicago may have lost that vision, but the experience of the dispute with Warner, and recording two out-of-the-ordinary CDs back to back, may have rekindled some of the fire that was there two decades ago. "[That work] was a real positive thing that we hadn't done for a very long time," admits Lamm "We hadn't done it since I would say the '70s. And that's really the way this band thrives. And I think everybody, in doing that, remembered, oh yeah, that's why it was happening. So I think now whatever it is we want to do next, we now have a handle on how to go about it."

Chicago plays at 7:30 p.m. on Sunday, July 16 at the Cynthia Woods Mitchell Pavilion. Christopher Cross opens. Tickets are $10 to $40. For info, call 629-3700.