iPhone app developers Smule are following up their best-selling I Am T-Pain app with another music-focused one, this time with TV show Glee. Created in conjunction with Fox Digital Entertainment, the app allows users to sing along to the cast to select songs featured on the show. But as this is Smule, there are a few twists thrown in.

On the music side, the app helps aspiring singers along with pitch-correction technology, so the recorded version of the karaoke song actually sounds listenable. It also breaks down users’ vocals into three-part harmonies.

On the social end, users can create their own Glee clubs to record a song with multiple friends from around the world, all singing the same song. Or they can use the app to tune into others singing any of the included songs, either individually or a worldwide chorus that blends the recordings of hundreds of users into a single song, harmonized using the company’s technology.

One cool feature lets you listen in using a virtual map. The voices of other users nearest you are louder than those further away. Users can rate other singers, and even invite them to add their voices to their own recordings.

Like the T-Pain offering, Glee app users will be able to download new tracks, this time on a weekly basis based on the songs included in the show, and has a freestyle mode that lets users sing whatever they want.

Check out the company’s video showing off a Smule employee using the app, complete with pitch correction and automated three-part harmonies, on YouTube. The app is available for the iPhone, iPod Touch and the iPad, and costs $3.

Smule co-founder and chief creative officer Ge Wang talks about the vision and challenges of creating the Glee app, and his overall thoughts on the music app market, in the interview below:

This is the first iPhone app you’ve released since I Am T Pain last September. Why was this the logical follow up?
We weren’t really looking for a follow up to TPain. This was designed from the ground up. It came about from an idea we had earlier, before we were approached by Fox to do the Glee app, to do some kind of crazy karaoke-on-crack kind of app, where you could add up to 1,000 voices from around the world to a song. That idea was floating around, but it wasn’t until we talked to Fox that it really crystallized. Not just technologically, but really spiritually. If I were to ask 'what is Smule all about?' I’d have to say three things. One is expressive audio. Two is through technology, setting the stage for people to unlock their creativity and make their own music. And thirdly is a social component that connects people somehow.

That seems a common thread with all your apps.
Yeah. What we’re really trying to do is connect people. But we need those first two aspects to bring people to that social experience.

Is this Glee app the ultimate representation of that vision?
I think there’s a lot more to go on that. We talk about mobile computing, and think about things we can do on mobile that we can’t do anywhere else. I’m wondering in the longer term, not just for Smule, if the word mobile will disappear from the phrase mobile computing. It’ll all just be seen as computing, and the distinction between mobile and non-mobile will just disappear. Yet we still have these mobile devices that really transform how we live. In there is the opportunity for us is to change the way people can be creative and make music.

What’s the impact of that for the music industry?
What we’re focusing on right now is for the masses, to enjoy and record music and be active participants. Making music should be as easy as picking up your phone and calling someone. That doesn’t exclude the artists, some of whom are natural leaders, from this venture. But we’re really trying to reach the masses with experiences that are not overly complicated but also not overly simplified.

How long did it take to put the app together?
I can’t get into specifics, but it was an insanely short period of time. It’s on the order of not quite weeks, but smaller than months. It’s been crazy. Part of the reason we wanted to launch this week was because of the next nine episodes of Glee starting up. So we gave ourselves a pretty hard deadline. It’s probably one of the most technologically sophisticated apps we’ve ever done. To give you an idea, for the last four weeks the team was probably working 100 hour weeks. They wouldn’t to that if we didn’t believe what this could be.

This Glee app came about as a result of you having an idea that needed an application. What ideas are floating around Smule today in need of an app to call home?
Well without going into too much details, there are things we want to do. Anything from mixes to remixes to jamming together from different locations to playing different types of music; new interfaces for musical expression and the proliferation of people taking to computers to make music. And so there are a number of ideas there we’d love to bring to the foreground. It all revolves around a collaborative music making experience.

You worked with artists and labels on the T-Pain app, and with a TV studio on Glee. Are you still interested in working with the music industry?
Definitely. We always have our ears open, if it fits the bill with what we want to do. If there’s that natural synergy, we’re going to embrace those opportunities. But it needs to be a mutual win.

Are you currently working on any projects with the music industry?
We are exploring a couple of different possibilities. I can’t say who yet. We want to do justice to who we work with and find the synergy that works for us, both from the business side and the creative side. So we are talking to different artists, but its mostly exploratory at this point.

What’s you view on the new iPhone software. Has that opened any new doors?
I think its going to improve and enable a number of the things we do. The background processing is very interesting. And there’s an interest from Apple to connect gamers together via the Game Center. I’m wondering what that means from a social gaming point of view. Whenever the word social comes into the sentence, my ears perk up.