Harnessing the split-second timing, turntable magic and tempo sync required for DJing from your computer is no easy trick, and German developer algoriddim (djay-software.com) has done an admirable job in djay 3 ($49.95). This dual-turntable emulation links seamlessly to your iTunes library, making all of your songs instantly accessible as DJ fodder. When you want to just sit back and be entertained, let Automix take over and select tunes from any playlist or from tunes you've dragged to the Automix bin. You can choose a transition style (break, echo, backspin, reverse or standard) or let Automix randomly choose among them.
Djay 3 is not just a toy; you can use it to spin new loops from old as well as for unusual sound design, and you can record the results on the fly (see Web Clip 1). The first step is to import your source material into iTunes and, perhaps, organize it in its own playlist. When you drag a clip onto one of djay 3's turntables, the software analyzes its tempo and aligns it to the beat. For rhythmic material, the tempo detection is quite accurate. When the tempo detection is off, it's usually doubled or halved (still usable), and there is a tap-tempo option, but I couldn't get useful results from it.
Most common DJ functions — cueing, skipping, beats looping, speed and pitch-bending, etc. — are one-click operations with ergonomically mapped key commands. A robust MIDI Learn implementation lets you map your favorite control surface to every function. In addition to built-in pitch-shifting, echo and reverb, you can insert an AU plug-in effect after each turntable, but only the generic AU slider interface is supported. Djay 3 is loads of fun. Check out the save-disabled trial version and see for yourself.