Oberheim's top-notch MIDI controlling keyboard, the Xk, is well thought-out, strongly built and offers plenty of handy features. But it faces some strong competition.

Back in the mists of time (about 18 months ago), a couple of companies introduced the idea of the MIDI controller keyboard, a mechanical device that made no noise at all, but simply acted as a means of controlling machines (expanders) that did make noise.

MIDI controller keyboards haven't been a runaway success in the UK, where it seems many musicians still prefer their musical instruments to reside in one box, rather than two or three. But the manufacturers have persevered with the modular approach, and now, expanders are becoming almost as common as their keyboard brethren, while several popular polysynths benefit from being played from a dynamic controller. One advantage of a controller keyboard over a synth or sampler (or even the new MIDI electronic pianos) is that it can allow you to create all sorts of sonic configurations of slave instruments, without imposing its own (inappropriate) sounds.

Add to this the fact that designers seem to be getting the hang of what other advantages a remote controller can offer, and the current plethora of new arrivals in this area begins to make sense.

The key to designing an effective controller keyboard lies in devising a system which is flexible enough to be useful, yet isn't too unwieldy to be practical. This is an area in which American companies such as Oberheim and Sequential seem to excel, so it's no surprise that the former's Xk controller keyboard is straightforward to use. Much of this has to do with a sensible front-panel layout, a successful compromise between digital parameter access and the older style of dedicated knobs and buttons. All parameters are listed on the panel and clearly grouped into related functions, with each group having its own LED and a selector button which allows you to loop around all the parameters associated with it. When you've selected the parameter you want, you can alter its value using the numeric keypad and increment/decrement switches (parameter values are shown in a two-digit LED display).

I found myself taking to this system very quickly, and what's so pleasant about using the Xk is that it allows you to do what you want to do with minimum fuss and maximum speed. Which is, after all, no more than you should expect from an instrument that's all about control.

Unlike Roland (MKB1000) and Yamaha (KX88), Oberheim have kept the Xk's keyboard to regular synth proportions, ie. five octaves. However, you can instantly adjust this range up or down two octaves in octave steps, and since held notes aren't affected by the octave change, you can play simultaneously over a wide pitch range.

And you can do a great deal more with this set of keys than you can with most. Two keyboard velocity scales can be selected, allowing you to choose between greater sensitivity in the middle or upper value range, while it's also possible to select the maximum velocity value that can be transmitted. Scales and settings apply to both attack and release velocities.

The Xk shows its Matrix lineage in its adoption of three keyboard zones, each of which can have its own user-defined range from one note to the entire length of the keyboard - so you can split and overlap zones in any way you want. This wouldn't be of much use unless you had some way of distinguishing zones, though, so you can program a MIDI transmit channel (1-16) for each zone.

Xk also allows you to program a patch number for each zone, which means you can send out up to three different patch numbers on three different MIDI channels - which goes some way towards alleviating the usual problems of aligning patches. Included for Matrix and Xpander owners is a facility for selecting single or multipatches, too.

Further zone-programmable features are the number of notes that the zone can play (up to 16), a transpose value (up an octave in semitone steps), MIDI Mono mode on/off, aftertouch transmit on/off, levers transmit on/off, and values for the continuous controller, footswitch and negative lever.

Setting a note limit under 16 for each zone brings the Xk's 'note spillover' system into action: any notes active in a zone over and above the specified amount are automatically sent on the next higher MIDI channel.

Lots of functions, then, but also lots of buttons to press each time you want to select a few of them. To avoid this, the Xk can store complete settings in any of 100 Master programs - equivalent to the Multipatches found on the Matrix synths and the Xpander. Oberheim haven't included the ability to chain these programs together and step through them with a footswitch, though, so it isn't as useful live as it could be. As it is, tapping in a two-digit number can instantly change your sonic configuration from piano, strings and harmonica to didjeridu, organ and gunshot. Being able to choose which pitch ranges these voices sound over, and which sounds respond to performance controllers (pitchbend and sustain, for instance) is potentially invaluable for both live and studio work. And the ability to multisplit a synth keyboard for MIDI data transmission is still rare, so the Xk really scores here.

You want programmable performance controllers? You got 'em. The Xk has two levers, one dedicated to pitchbend and the other programmable in forward and 'negative' directions, a 'continuous controller' slider, and a single footswitch input. Between them, they can be set to any of the 96 MIDI performance controller numbers, which means you can control any MIDI-introduced effect such as modulation, volume, sustain or portamento. The negative lever, continuous controller slider and footswitch are programmable per zone as well as per Master program, which rather usefully allows you to (say) sustain one of two layered sounds, but not the other.

The Xk also includes arpeggio, Chord and Hold facilities which may be associated with any one of the three zones; you can accompany yourself by playing on the keyboard whilst an arpeggio is playing back. The arpeggio's tempo can be controlled in real time from the front panel, but Oberheim have also included an external clock input designed to interface the arpeggiator with the Click Out (positive-edge trigger) of a pre-MIDI sequencer or drum machine, which might appeal to users of Oberheim's own pre-MIDI gear, for instance.

Hold allows you to sustain up to 15 notes indefinitely (providing you're using sustaining sounds, of course), while the Chord facility allows the notes input using Hold to be one-finger-played as a chord (with suitable transpositions) from any note.

Personally, I'm not sure about this aspect of the Xk's design. While some players will find the arpeggiator useful, I can't help feeling an onboard sequencer (even a fairly straightforward one) would have been a more tempting option.

And it's in the area of sequencing that the Xk poses an interesting problem. Modern sequencers invariably see MIDI recording as being based on a single channel; in other words, any given performance is allocated to one MIDI channel, either at the time of recording or retrospectively. Yet the Xk allows you to play over three MIDI channels simultaneously, with different patch-change and controller information for each channel. So how can you record an integrated multitimbral performance in the way that the Xk allows you to perform it? Tricky one.

Appropriately for a MIDI controller, the Xk allows you to trigger MIDI sequencers and drum machines from its front panel. You can send Start, Stop and Continue codes and MIDI Song Select numbers, but beyond that, you can't control the tempo or the position of a sequence remotely from the Xk, which is a pity.

Also included is the ability to send a MIDI Tune request and an All Notes Off command. The former isn't MIDI's version of Family Favourites, but an instruction for analogue synths to tune their oscillators. The usefulness of the latter (which is intended to offer a quick solution to those potentially embarrassing situations where notes are left hanging for some reason) is limited by the fact that not all synths respond to the command; like several other grey areas of the MIDI spec, its implementation was left optional.

For me, the idea of a separate controller keyboard is beginning to make more sense - though only if you've already got enough instruments to make it worthwhile, and enough money not to wish you'd bought a synth instead.

The Xk has plenty to recommend it, not least in its happy balance between flexibility and accessibility. Its three keyboard zones, together with the parameters that are definable for each zone, make it more flexible as a controller than any synth I can think of other than Oberheim's own Matrix 12. The plastic keyboard has a shallow travel, is pleasing to play, and responds to attack and release velocity and channel aftertouch - though not polyphonic aftertouch. It won't please the piano fans, but it's nicer than most ordinary synth keyboards.

The problem is that the Xk sells at just over a grand, which is not cheap, especially as it faces imminent new competition from Roland, Akai and Bit. But it's a neatly thought-out and durable instrument, and I wish it well.

Price £998 plus VAT

More from (Contact Details)