Native Instruments' Traktor has long been one of the most popular DJ systems in the world, but it's always been fairly expensive and somewhat challenging to use. That's all changing today with the release of Traktor DJ for iPad, a $19.99 app that turns Apple's tablet into a fairly complete DJ interface that's extremely fun to play with — and powerful enough to actually do some real mixing in.

Unlike most other popular DJ apps for the iPad, Traktor DJ doesn't have any virtual turntables or other real-world controls displayed on the screen — instead, you directly touch and manipulate the waveforms of your tracks themselves. Traktor immediately slices beats into tappable areas as it loads tracks from your iTunes library, so you can jump around in a song simply by tapping on the waveform, and you can set loops anywhere just by tapping with two fingers on the screen. Once you've got a loop set in place, you can move and change it just by pinching and sliding — it's a little strange at first, but it makes sense after a couple minutes. Loops and cue points can sync with Traktor Pro on the PC, so you can use the iPad to prepare tracks for later use — and it's clear that there's more integration planned, although NI is being coy about where it might go.

Adding effects is similarly easy — you just open up the EQ and FX panels, and then you can drag your thumbs around a grid that maps intensity and mix. It's kind of like playing a video game, in a way. There are several built-in effects, including reverb, delay, a beatmasher, and filters, and you can lock settings once you've got things where you want them. You can also record mixes right in the app, and you can split the left and right headphone channels so you can cue tracks using headphones if you plug in a splitter. And if you're really serious you can use one of NI's USB audio interfaces through Apple's iPad Camera Connection Kit for stereo audio output.

Perhaps most interestingly, Traktor DJ teaches you how to use the software as you move through it — the help system is integrated into a small notification system. The number of notifications decreases as you use the app and discover features, and tapping on the icon reveals all the features you haven't yet used along with instructions on on how they work. It's a clever way to get people into the tutorials while still allowing them to start playing with the app right away.

And there's even more help in store: Traktor DJ also does harmonic analysis of your iTunes library and can suggest tracks that will work well with what you're already playing, and there's automatic beat matching and even downbeat detection, so just hitting play will start your next track in sync with what's currently playing. It's basically doing the basic parts of DJing for you, and it's sure to irritate DJ purists. But NI's head of product design Jim Mazur wasn't too worried about it as he demoed the app for us. "Getting two tracks up and running and really playing with the music is so much more exciting than trying to get to that point," he said. "I see this as a great afterparty thing — your gear is somewhere else, so you pull out your iPad and start having fun."