THE FULL STRETCH

Oberheim Xpander Analogue Synth Module (Retro)

Published in SOS January 1998
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Reviews : Sound Module

Being analogue in 1984 was not really a plus point for a synth. Everybody wanted digital, and Yamaha's DX7 was dominating the synth market like nothing else had before or since. But despite such competition, and a scary price tag of about the same as three DX7s, the Xpander flourished while other now-revered classics sank without trace.

At the time, much was made of the Xpander voice. Even today the module's complement is still undoubtedly special. Each of the six voices is made up of hardware for the audio path and software for controllers. There were two VCOs -- real ones, too -- for a richer sound, a 15-mode filter and two audio VCAs, with software for the multitude of envelopes, LFOs, ramps, tracking generators and the like.

The VCOs have mixable Triangle, Sawtooth and variable pulse waves. Oscillator 2 has a sync setting and white noise, and you can also cross-modulate the oscillators for an analogue FM fuzziness: although the

MEET THE FAMILY     The Matrix 12, released nearly a year after the Xpander and costing a substantial £5980, is essentially the innards of two Xpanders plus a 5-octave keyboard. It has the same sounds and features. If you come across a Matrix 12 second-hand, don't be surprised at an asking price of £2000-£2500. The Matrix 6 and 6r, and their cousin the Matrix 1000 (pictured above), are what the industry calls costdowns, featuring DCOs instead of VCOs, a low-pass filter, and fewer envelopes and LFOs. All this means a marked reduction in programming options, which could be a blessing, I suppose! Only the Matrix 1000 is a current instrument, with sound editing via software or with external hardware such as the Access programmers (see SOS September 1996 for a review).

effect here is not as strong as on a Memorymoog or Prophet 5, it still produces some good bell sounds. One nice touch is that each VCO has its own VCA, so you can adjust the volume of an oscillator with any control source, useful for creating complex layered sounds without eating polyphony.

Most synth users find the filter gives a synthesizer its character and uniqueness. On the Xpander, instead of the ubiquitous low-pass design, there are 15 filter modes -- low-pass, high-pass and band-pass, notch (the reverse of band-pass), and phase-shifter -- all in various rolloffs and combinations. And this was when high-pass filtering was seen as exotic! The range of sound options instantly available is huge. Just grabbing the filter mode knob and changing from a simple low-pass to a high-pass with phase shifter will transform any sound. The filter also has a three-pole low-pass mode of the kind favoured by the TB303 and its clones, for instant dance appeal, with weird resonance too.

For the sake of cost, reliability, and probably portability too, the envelopes and LFOs are software generated. Some pundits claim software gives a different (read lesser) quality, when compared to real hardware. I've compared my Xpander to an older OBXa and there seems a common sound identity to both Oberheims, so I'm not sure I'd agree in this case. One drawback of using computer generation, however,

FAMOUS NAMES     Xpander/Matrix 12 users include: Vince Clarke Nine Inch Nails Technotronic Yello Stockhausen Steve Lipson Propaganda Keith Emerson Joe Zawinul

is that everything must be quantised. Envelope times and LFO frequencies on the Xpander are quantised to 64 steps. (Some other parameters have 128 steps). At first this sounds like a shortcut to disaster, but I'm pleased to be able to tell you that things work out well. Chosen values are concentrated in the ranges you need most, so you do seem to get the setting you want. Interestingly, zipper noise seems to be almost undetectable too.

Say "Oberheim" and old analogue anoraks think modulation. Like virtually every commercial synthesiser since the Minimoog, the Xpander has some standard modulation connections hardwired (12, in this case). But buyers of the Xpander had access for the first time to the now-infamous Matrix Modulation system and, consequently, dynamic control of nearly every sound parameter -- lots (and I mean lots) of sources, with loads of things to control. And where one LFO and a couple of envelopes were good enough before, the Xpander featured five of each. Per voice! These envelopes are no

"The Xpander's influence can be seen in most American designs, from the 80s to today"

cut-down versions, either -- they're DADSR (Delay, Attack, Decay, Sustain, Release) types, including a delay parameter and various trigger and run modes. The LFOs have a claimed 64 different waveforms, including noise and a sample setting for creating staircase effects and the like. There's also a global LFO for normal vibrato duties. In essence, the Xpander delivered modular synth flexibility in a commercially available, programmable analogue package.

The Xpander's software matrix lets an intrepid sound hound connect any of 27 sources to one or more of 47 destinations, with up to 20 connections per voice. Some options are obvious, others less so. Oberheim's design thoroughness means that hard-wired options are duplicated on the matrix, which is useful when further manipulation is needed. The result is not only limitless Joe 90 boffin appeal but also serious potential for sound creation, which can be used subtly or otherwise, depending on what you're

"This is a synth with the kind of features that every player has dreamed about."

after.

There are some unusual modules too -- 5-position tracking generators, three per voice, which the manual says change a linear input, such as a keyboard, into a non-linear one. You may wonder why you'd want to do this. Well, perhaps you might want a low-pass filter to track the keyboard, so that the sound is dull across the middle two octaves but bright at both ends, or maybe you'd like to vary the amount of PWM across the keyboard, to lessen the mushiness at one end.

And the features don't stop there. Each voice has four ramp generators, often used for fades and sweeps, and a lag generator, which slows down voltage changes. This is ideal for portamento, but it can process

WHERE ARE THEY NOW?     Tom Oberheim has his own company, Marion Systems, which produced an Akai S900 upgrade and a couple of Matrix 6-type modules, but seems to have been quiet lately. Michel Doidic, credited with matrix modulation, and Marcus Ryle still design synths in the mainstream, going on to become involved in today's Alesis range. Anyone interested in further reading should check out the June 1993 issue of SOS for an interview with Marcus Ryle, and the March 1994 issue for a Tom Oberheim interview.

anything from velocity response to LFO shapes and pedal inputs. I'm sure you get the idea by now.

With all this going on, you need a clear control panel, and Oberheim did a pretty good job of providing one. There was no way that an Xpander with one knob for each parameter could fit onto a keyboard stand, so there had to be a compromise. They chose lots of buttons, and six click-stopped continuously rotatable knobs. The system works very well too -- most of the parameters you'll want to twiddle can be adjusted quickly.

The panel is divided into easily digestible sections, which are called up in pages. A section's main parameters are then listed on one display for instant editing, with values listed on a second display below. In the case of an oscillator, for example, frequency, pulse width, volume and so on, are named, and each has its own dedicated knob. When you turn a knob clockwise it adds to the stored parameter value, while an anti-clockwise turn subtracts from it. If you wanted to modulate something, you'd simply press the soft

X-RAY SPECS     MODULATION SOURCES5 LFOs 5 envelopes 3 tracking generator 4 ramp generators Lag processor 2 pedal inputs MIDI velocity MIDI release velocity MIDI pressure 2 MIDI levers MODULATION DESTINATIONS Oscillator 1 frequency, PWM Oscillator 2 Frequency, PWM 15 VCAs VCF frequency, resonance FM gain Envelope parameters LFO: Frequency, amount FILTER MODES 1/2/3/4-pole low-pass 1/2/3-pole high-pass 2- and 4-pole band-pass 2-pole notch 3-pole phase shifter 3-pole phase + 1-pole low-pass 3-pole high-pass + 1-pole low-pass 3-pole notch + 1-pole low-pass 2-pole high-pass + 1-pole low-pass THE VOICE 2 VCO 1 VCF (15 modes) 15 VCAs (some in software 1 FM generator 1 lag processor 5 digital envelopes 5 digital LFOs 4 ramp generators 1 noise generator

button next to the chosen parameter displayed and jump straight to a page where envelopes and LFOs can be assigned and their amounts adjusted.

To be fair, there is quite a bit of leaping from page to page, and this can be a bit of a pain. The alternative, however, could have been editing with a single slider and small display. Not nice!

As well as having loads of features, the Xpander sounds good -- very good, in fact. Compared to earlier Oberheims, or Moogs and ARPs, the Xpander has a smoother, more sophisticated timbre. Put it next to a Moog or ARP and it sounds mellower, with a more polished '80s feel. Although this was possibly due to different Curtis chips used in the later synths, the Xpander's sound seems to continue a trend by Oberheim towards a less raw tone than their earlier machines. Tom Oberheim has since said that he now prefers the sound of his earlier instruments over the OB8, Xpander and Matrix series, but didn't comment on whether this was what he thought at the time. Don't get me wrong -- there's still clout and class here, easily enough to see off the virtual analogue brigade. But the heavy-duty Van Halen patches are just not so convincing, and the Xpander's strengths lie in a slightly different area. What you get is a solid and much more expressive sound, helped, no doubt, by lots of controller possibilities, including touch response.

The Xpander stores 100 single patches, and names for each of them. It's 6-part multitimbral, which was virtually unique in 1984, and (beating the Korg M1 by a few years) it has a zoned multitimbral performance mode too. There are 100 of these 3-zoned setups, which will seem very familiar to Korg and Kurzweil users! For each zone you can choose any MIDI channel and note range, for splits, layers or multi-channel operation. Volume, transposition, voice assignments, and panning or separate output selection can be set for each voice. You can even edit voices within a multi on-the-fly.

Some people are going to love this. Thoughtfully labelled on the back panel are stereo audio outs and six individual voice outs, plus individual CV and gate inputs, MIDI In, Out and Thru. Yes, folks, it's a MIDI-CV converter (except that CV has to be the controller). A Trigger In socket, three pedal inputs, including Program Advance, a cassette interface (though you are more likely to use SysEx today) and power complete the picture.

The Xpander is probably not going to be your only synth. It's analogue and only makes analogue synth noises. As I've already hinted, it lacks the raw punch of a Moog, and hard, percussive sounds are not its strongest suit. For modular analogue purists the fact that the signal path is fixed at VCO-VCF-VCA, and the knowledge that many parameters are quantised, could be a disappointment, although in reality it probably won't be. I could also reveal that setting up multis is a bit long-winded. But hey, we're getting picky.

GOOD BUY?     As with all synths of this age, a second-hand Xpander should be bought with care. Xpanders I have been exposed to seem fairly well behaved. But look at the external condition, and see how it behaves when switched on. Don't be put off by this, but all Xpanders seem to go berserk occasionally. (It's in the software, you know!) Turning it off and back on again should clear the problem.

Make no mistake, this is a very fine, important and influential instrument. Its influence can be seen in most American designs, from the 1986-vintage Ensoniq ESQ1 through to today's Alesis, Emu and Kurzweil machines, and matrix modulation is now widely available on instruments from a range of manufacturers, both American and Japanese.

For Oberheim, the Xpander was a very important instrument. They chose to stay with analogue. The Xpander and its offspring kept them in business when other purveyors of American analogue couldn't sell enough units to keep the doors open. People wanted new and interesting instruments, and the Casio CZ, Yamaha DX and sampling technology took the sales. Roland and Korg analogue-based synths also took a serious knock from this trend, but these companies had the muscle to diversify into effects processors, pianos and amps. Oberheim continued, though it changed hands in later years, and even today, nearly 14 years on, you can buy a direct descendant of the Xpander in the shape of the Matrix 1000. High praise indeed.