NEW YORK (CNN) -- The members of the band Naturally 7 are experts at blowing their own horns -- and they do it without a trumpet or trombone in sight.

Naturally 7 engages in "vocal play" in performance, emulating the sounds of musical instruments.

In fact, you won't see a single instrument when they hit the stage. They are the instruments.

"People are always imitating instruments," said first baritone and arranger Roger Thomas. "People are driving; they hear their favorite song; it gets to the guitar solo part. ... They don't stop singing. They actually start imitating the instrument they hear. We just decided to be crazy enough to bring [that idea] to the stage."

The septet even came up with a name for it: "vocal play," a total reliance on the human voice to mimic a range of instruments and sounds, including the harmonica, bass guitar, trumpet and DJ scratches. Watch the band do its thing »

Warren Thomas takes beatboxing to a whole new level with his imitation of a drum kit, complete with snare. (He also impersonates a mean guitar.) Rod Eldridge has never played a real trumpet before, though you wouldn't think that if you saw him duplicate the sound of one, lips pursed, his hands in front of him, pressing on imaginary valves.

"To produce the sound, I have to visualize that I'm holding that instrument or whatever in my hand," he said.

Only one Naturally 7 member has ever played the instrument he imitates, and that's Armand "Hops" Hutton, who uses his incredibly deep voice -- you have to step closer when he speaks -- to portray a thumping bass guitar.

Don't Miss

The group initially formed a decade ago in New York as an a cappella group (oh, yeah, they sing, too). But to make themselves stand out, Naturally 7 decided to be both a singing group and a band.

The concept caught on when video of them performing on a Paris subway -- to hilariously mixed reactions from Parisian commuters -- hit YouTube. It has racked up almost 3 million views. And standing ovations became a regular part of the group's experience touring as the opening act for crooner Michael Bublé in 2007 and 2008.

The musicians are about to embark on their own tour of Asia, Australia and Europe. With a recent performance of their aptly named song "Wall of Sound" on "The Tonight Show with Jay Leno" and a new album in the works, they hope to boost Naturally 7's profile in the United States over the next year.

Naturally 7 -- which also includes Jamal Reed, Dwight Stewart and Garfield Buckley -- spoke to CNN about the challenges of becoming instruments. The following is an edited version of the interview.

CNN: Traveling and sound checks must be very easy for you.

Roger Thomas: We don't have to lug around instruments with all the traveling we do, and that does make that part easier. The sound check part of actually becoming the band, where we're actually the singers and the instruments, that probably takes a longer time.

CNN: How so?

Thomas: I often call our sound man "Octopus Hands" because he's just got to do so many different things. We switch from being the backgrounds to being the lead vocals and then going back to doing a trombone. And these have different sounds and settings, so it's a lot of work on the performance side if we're using microphones.

CNN: Are your "instruments" ever out of tune?

Rod Eldridge: Every now and then. It is the voice, and if you're suffering and you have a cold, its not like you can have a guy come in and [say], "Oh, let me change my guitar string out." It's a human thing. Every now and then, you're not as perfect as you would like, but you are always working at it.

CNN: Are you continually adding new instruments?

Thomas: We definitely are. When we hear something that's brand new, we'll just try to get really close to that sound. There are a couple of things we can't do, like a piano. Piano is like a percussive and a string instrument at the same time, so we leave pianos alone.

CNN: Who has the hardest job here, do you think?

Thomas: I think we all think we have the hardest job. (laughs) Probably Warren. He has to keep up that drum flow for songs that go for five or six minutes and shows that go for almost two hours. That's a pretty difficult job.

CNN: You were the opening act for Michael Bublé for a while. That must have been a great way to introduce you to a whole new audience.

Armand "Hops" Hutton: Yeah, it was great. We started off with him in Rotterdam, and I don't think we were supposed to keep going after Europe, but the marriage between his set and our set was just so perfect that he kept saying, "I want to introduce you to my fans here, my fans there." We've been to Australia and Canada ... all over the world.

CNN: How do people respond when you perform?

Thomas: Shock, usually. On the Bublé tour, it would take people usually by the third song to actually get it. By then you can see them bouncing around, hitting each other, going, "This really is all voice!"

CNN: Are you working on a new album?

Thomas: We are working in the studio right now, getting ready for what will probably be our first world release. We don't know what we are going to call it yet, but we do know one thing: It will be all vocal.

All About Music • Michael Buble