Let's get the technical details out of the way. Like many current apps, Traktor DJ requires an iPad 2 or better running iOS 6. All tracks must be loaded in through iTunes, so you might be strapped for space if you're running a 16 GB iPad with a bunch of apps already installed. Traktor DJ does support Core Audio, which means you can use compatible audio interfaces like the NI Audio 6 or Audio 10 (with a Camera Connection Kit). If you just want to use the iPad's headphone output, Traktor DJ provides the option to split the left and right signals so that you can cue tracks by way of a splitter cable. This method results in a mono mix output, but most club sound systems aren't wired for stereo anyway.
Once you've loaded up with tracks and opened Traktor DJ, what awaits you? We were pleased to find that NI's strong design acumen is immediately evident, as nary a pixel of screen space is wasted. Rather than the typical spinning-vinyl UI, they've embraced the touchscreen paradigm. Two of the same waveform display found in Traktor Pro are stretched to fill nearly the whole screen, and you can interact with tracks in a variety of intuitive and futuristic-feeling ways just by manipulating them with your fingers. You perform tasks like setting loops and cue points, scrubbing through tracks and even triggering slices of a loop simply with different gestures.
The two decks have individual EQ and effects panels, accessed by buttons on the right side of the screen. Their controls pop up and overlay the track waveform. The EQ panel has the typical three-band delay and volume fader, controlled by multi-touch sliders that allow you to hold a value with one finger and jump to other values with a second. The EQ also contains a filter tab for controlling the same powerful filter from Traktor Pro (and the Traktor Kontrol Z2) via an XY pad. Each deck has three effects slots, and you can select from an array familiar to Traktor Pro users: delay, reverb, low- and high-pass filters, flanger, Gater, Beatmasher 2 and Digital Lo-Fi are all on board. Unlike Traktor Pro, however, only one slot can be active at once. As soon as you start to control one effect, any active effects for that deck are disabled. We found most of the effects to be the same high quality as their Traktor Pro counterparts, but the reverb fell short in listening tests. We'll give NI a pass on that one: reverbs can be CPU-challenging, and the iPad only has so much juice to go around. Perhaps future versions of Traktor DJ could allow for a higher-grade algorithm to be selected on iPads with faster chips.
Each track loaded in Traktor DJ is analyzed to build the waveform display and to detect the beatgrid and tempo, just like in Traktor Pro. Traktor DJ, however, adds key detection to the analysis. As soon as a track is analyzed, the key is listed right next to the tempo. (It's represented in Open Key Notation, though, so it may not be obvious to some.) NI takes full advantage of this attribute with a new recommendation engine that shows you the tracks matching the tempo or the key of the currently playing track. You can also browse by key in addition to the other expected categories (tempo, artist, album and genre). It's an incredible addition that we have to assume will make its way to Traktor Pro as well, and for it to have been introduced first in an iPad app is pretty astounding.
Although Traktor's analysis engine is as strong as any out there, some tracks still require hands-on attention to correct beatgrid issues. Doing this by mouse in Traktor Pro can be burdensome, but NI hit the nail on the head for the iPad. Traktor DJ provides a dedicated mode for this, and tracks can be corrected while they play, both for tempo (by tapping) and for phase (by dragging the waveform across a four-bar overlay that flashes with the beat). Any analysis, beatgrid corrections or cue points you've set for a track can then be synchronized back to Traktor Pro by way of Dropbox. There are some caveats to this process, though: you can synchronize multiple iOS devices, but you can only sync to one copy of Traktor Pro, for example. (More notes on this process and its constraints can be found here.)
So how's Traktor DJ in use? You may have noticed no mention of tempo faders for the track decks: there are none. If you really want to beatmatch manually, you can do so with a little trickery by turning sync off for one track and using the global tempo adjustment wheel to control the other. But with no way to nudge tracks, you'll only get so far. It is clear that Traktor DJ is at its best when users embrace the technology at their fingertips and use the sync button, concentrating on mixing and effects instead of beatmatching. My only quibble is that the filter shares a panel with the EQ and volume controls, so there's no way to control both at the same time for a given track. This brings a new level importance to Traktor DJ's always-available crossfader, which performed dutifully in my test sessions.
Overall, I was blown away by what Traktor DJ brings to the table for $20. On its own, it's a capable DJ app that you could certainly use to play house parties or even clubs (if you're secure enough to work through the stigma of being an iPad DJ). But where I see it excelling most in the serious DJ world is in track preparation. I think we'll see more and more touring DJs taking an iPad on the road and organizing their sets between gigs with Traktor DJ. With the synchronization options available, the new key detection algorithm and the ability to correct beatgrid issues easily, Traktor DJ became an incredibly useful tool for any Traktor Pro user the moment it arrived.
Ease of use: 4.5/5