touchdj

Amidio makes some heavy-duty musical apps for the iPhone and iPod Touch; I was particularly impressed with StarGuitar, which gives you a virtual guitar with a bunch of preset rhythms, letting songwriters create quick sketches of ideas when they're nowhere near a guitar.

On Tuesday, Apple approved a new Amidio app, called TouchDJ, for the iPhone and iPod Touch, and it's both very impressive from a technical standpoint and a heck of a lot of fun. The iPhone can only play one audio track at a time, but TouchDJ essentially fools it into placing two MP3s side by side for simultaneous, real-time manipulation and playback. It's like a two-track digital DJ setup right on your iPhone.

You get a crossfader to control the balance between the two tracks, plus individual controls for each track's volume, pitch/speed (which aren't independent from one another, unfortunately), equalization (three bands), and effects (the built-in real-time effect sounds like a kind of flanger, and there are several lame samples of a low-pitched robot voice, but you can upload your own). Each track is represented by simple waveform images that use a different color for the bass, which helps you match beats more effectively. A tempobend effect, which lets you quickly bend the speed up or down on either track, also helps you get in sync.

The looping functions were most impressive--you can create a cue and loop mark at any point in either track, then return to the cue with the rewind button, move to the loop mark with the fast forward button, or create an endless loop between the two points. All of this is in real time. If you've got an audio splitter, you can even create a separate cue track for your headphones--for example, to set up a loop in your second track while the first one is playing, without exposing your experimentation to your audience--although this requires some serious processing power, and is recommended only for an iPhone 3GS.

There are a couple caveats.… Read more