hpDJ: an automated DJ with floorshow feedback

Here’s a little gem for anyone else out there interested in dance music, DJ’ing, and computers: hpDJ: An automated DJ with floorshow feedback. Basically, it describes a system which allows one to define a “qualitative tempo trajectory” for a DJ set, then chooses tracks to fit the trajectory (the words “partial ordering” occur at this point, but that’s as close as we get to TCS), and automatically beatmatches/timestretches/mixes the tracks accordingly. Towards the end it considers the performance and “collaborative consumption as composition” possibilities, with genetic algorithms and the like, but the bit which impressed me the most was on the mixing, where the opportunities afforded by doing the job in software are recognised and made the most of.

However, because hpDJ operates in the pure software realm of digital signal processing (DSP), it is possible to create as many sweepable band-pass/cut filters as is desired for any particular cross-fade from one track to another. As with traditional hardware mixers, each DSP filter can have variables that control the degree of attenuation or boost, and its center-frequency. In addition to this, the shape of the DSP filter’s transfer function (e.g. the nature and rate of the fall-off or boost) and its bandwidth can also be under automatic control. Recording studios do have filters with these added controls, but such filters (known as a Parametric EQ) are too expensive to be built into each channel of professional mixing desks on a many-per-channel basis.

Thus, it becomes possible to specify hpDJ so that it analyses the audio frequency-time spectrogram for the incoming and outgoing tracks in the cross-fade, and uses a number of heuristics to determine how many DSP Parametric EQ filters are necessary and what their settings should be. This can be used to, for instance, selectively suppress the frequencies for a synthesizer melody-line in one track, attempting to make that melody “disappear” while keeping the bass-guitar and percussion elements in place during the cross-fade. By employing simple heuristics for detecting when one component of one track “clashes” with another component of the other track, such aesthetically unpleasant clashes (which may remain despite perfect beat-matching) could be automatically eliminated by hpDJ.

Note that this is all happening automatically (except maybe setting some initial loose parameters at the start) – very impressive.

Although this was published only in 2005 (I spotted it in this book on this man‘s desk), much of this was apparently done around 2000 or so. Thus, I wonder what goodies they’re cooking up in Bristol even as I type. Dave Cliff’s “inventor profile” page doesn’t really bring us up to speed, I feel… Aha! He’s moved to Southhampton.

Finally, I note that this is the first paper I’ve ever seen which opens with a Sisters of Mercy quote. Rock on.