In the middle, between the circular pad and the screen, is a touch-sensitive fader control, which is just as fantastically accurate and sensitive as the touchpad. Slide your finger along its track and a white LED follows your digit. This can be used to control the mix for both line-out and headphone outputs (there are two 3.5mm outputs on the bottom edge of the player), so you can fade in and out of tracks at will in private, leaving the final lineout fade to the end, once you've perfected the transition. Around the fader are several more controls: two buttons for switching between channels, fast forward and rewind controls, plus a play/pause and cue control.
Another key control is the thumb switch on the left edge that acts a bit like the Shift key on a keyboard, essentially tripling the number of things you can do with the controls on the face of the player. Push it towards the top when mixing and the touchpad can be used to adjust the speed of the active tune; pull it towards you and spinning your finger around its circumference adjusts the volume of the headphone output. Play with this long enough and you'll discover other stuff, such as loop tools and effects such as roll, echo and reverb.
The really clever thing here, however, is that the Pacemaker displays the beats per minute of each live track at the top of its screen (to an accuracy of 0.1 bpm), This can then be used to quickly match the speed of the upcoming track to the one playing, making beat matching a lot easier. Tonium's Pacemaker editor software - which also allows you to prepare mixes on your PC before uploading them - analyses tracks before they're uploaded to the device and incorporates this bpm data. One really fantastic feature this enables is that you can choose to browse tracks by speed range, making selecting an appropriate track from your potentially huge library an absolute doddle.
With a bit of practice, I was happily beat matching and mixing away. The results I achieved probably wouldn't pass muster at a hot London night spot, but the fact that I was able to achieve something close to passable within a few days is testament to the success of the user interface. The sound quality is excellent both from lineout and through the headphones, and it even manages to include a decent range of music format support: in addition to the usual MP3, there's support for AAC files (unprotected of course), plus AIFF, FLAC, WAV, Ogg Vorbis, and even the Unix SND format. Bizarrely, though, WMA is not on the list, which could be a problem.