There’s something to be said for software that does one thing well. Scratch DJ Academy MIX addresses a very specific need: it automatically analyzes songs--especially dance-friendly electronic tunes--for key and beats per minute, and then offers a limited selection of tools for joining matching songs together in DJ-style mixes.
 
And it does this quite well. Import songs into the MIX library, and after just a moment, the app brings up the tune’s BPM and key. Drag a song into the mix list, and the app highlights other songs that match either or both of those criteria. Pick a match-friendly tune, and the app intelligently blends the end of the first song into the beginning of the second, buffing over minor differences in tempo with a surprisingly successful beat-matching system. For further control, you can choose when in the first tune the second tune begins, adjust the length of the crossfade, choose the crossfade type, and even nudge the second track in 1/32 increments in case the two don’t line up exactly right.

Mix as many tunes as you'd like. Each crossfade can be customized in length, position, and type, allowing for many different effects.

As I say, it does all this well...when used as expected. The trouble arises when importing music that isn’t as consistent in key or beat as dance tracks--say, any jazz or rock number. In these cases, both the key and the BPM can be wildly inaccurate, making for some laughably inappropriate matches. You can adjust the BPM and key on a song-by-song basis, but this significant extra step is only useful if you have prior knowledge of the problematic song. That’s a shame, because one of the great joys of listening to a skilled DJ is hearing a mix of two songs that you’d never think would go together.

But that can be excused as not being the main focus of the software. Less excusable are the app’s more fundamental deficiencies, chief among these being the incomprehensible choice to not give the user any option of where in the latter song to begin the mix. Also problematic is the fact that, while the app can export your finished mix as an MP3, it does so only at a paltry 128Kbps bit rate. (Fortunately, WAV is also an export option.)

The bottom line. For would-be DJs with a large library of easily analyzed electronic tracks, MIX is a powerful tool for developing new mixes. But it’s less friendly to non-electronic libraries, and hence a lot less useful as more than a curiosity.