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Korg Z1

Polyphonic Physical Modelling Synthesizer (Preview) By Gordon Reid
Published August 1997

Korg's mission to bring musicians the benefits of physical modelling synthesis at an affordable price continues; you can now have a polyphonic, multitimbral Prophecy for well under twice the price of the original. The synth is called the Z1, and Gordon Reid is the man with the exclusive technical preview...

When Korg demonstrated the Z1 prototype at its launch in the Lloyds Building last month, presenter Paul Wiffen claimed that the new synth was born in the company's 'More' department... the one that satisfies the dealers' and customers' incessant demands for more of this, more of that and, most probably, more of the other too. This must be one of Korg's busiest divisions, because over the past nine years it has added more voices, more effects and more sequencing capabilities to every PCM‑based workstation since the M1. Similarly, it has expanded the Wavestation from its earliest incarnations through the EX, the AD, and finally the SR. Now the department has evidently got its hands on Korg's first physical modelling synthesizer, the Prophecy, and this has suffered more than most... The result is more voices, more physical models, and more performance options.


The Z1 is, in its basic configuration, five octaves wide and 12‑voice polyphonic, with each voice derived from a pair of physically modelled oscillators plus a sub‑oscillator and a noise source. Voices can be spread multitimbrally across six MIDI channels, making the Z1 the world's first multitimbral physical modelling synthesizer. Furthermore, you can derive each part from a different model and map it to a different zone on the keyboard.

Fortunately, Korg haven't limited their new baby to (and I quote) the "slavish imitation of analogue": the Z1 offers more than double the number of models found in the Prophecy. There are now 13 of these, each derived from the much‑touted but as yet unheard OASYS (Open Architecture SYnthesis System). Korg have never made this $10,000 mega‑synth available to the public, and it now looks more like a development platform for the company's affordable instruments than a product in its own right.

The Z1 offers 256 program memories, and these should be enough for most requirements. The 32 multitimbral memories are, however, firmly on the mean side, and I expect frustration to set in quickly. Fortunately, you can save Programs, Multis, Global settings and Arpeggiator patterns to PCMCIA cards. These, while expensive in the summer of '97, should become more affordable as the technology becomes more widely used. A 256K card will hold two complete dumps from the instrument, so a 2Mb card will hold 16 — more than enough for any requirement.

The Z1's keyboard is sensitive to both velocity and aftertouch, and this is complemented by 12 dedicated controls (four filter knobs and eight envelope knobs), pitch‑bend and modulation wheels, and four foot‑pedal inputs. Unfortunately, a dedicated input for a breath controller is missing. This is a shame, especially when you consider how many wind instruments the Z1 seeks to emulate. By way of redress, the Z1 is the first keyboard to offer a touch‑sensitive X‑Y pad, as found on latter‑day PowerBooks and some laptop PCs. You can assign a wide range of parameters to this pad and, since it's bi‑directional, control two of them at a time. Once you've decided the amount by which you wish to alter them, you simply touch the pad at the appropriate point, and then latch the result with a dedicated button. You create dynamic effects by moving your finger over the pad as you play. Even a few moments' experimentation proves that this system has impressive potential, making the Z1 much more expressive than it would be with just the conventional wheels and pedals.

Models & Effects

The Z1 retains all the Prophecy's physical models, including, of course, its analogue model. Based upon two DSP‑generated oscillators, two resonant filters, and two envelope generators per voice, the model echoes many classic monosynths of the 1970s. But, whereas the Prophecy was monophonic and was, therefore, comparable to a Minimoog or Korg 700S, the Z1's polyphony makes it more like a Prophet 10 or Oberheim Matrix 12. The Z1 even offers a Unison mode that allows you to assign two, three or six detuned voices to each note. Since the Z1 remains multitimbral in this mode, even the most revered analogue synths of yesteryear may soon find their over‑inflated reputations and excessive values threatened.

The analogue model also produces a limited range of percussion sounds. Moreover, you can edit these, so you're not restricted to the same old TR808 and TR909 noises — although if you are into these sounds, the Z1 will provide them for you.

The Z1 retains the Prophecy's string, reed and brass models, but Korg have modified them to take advantage of the X‑Y pad. The launch demonstration showed how you can manipulate a single sound — a bass guitar — using the touch‑pad to vary the timbre from muted strings to plucked harmonics. The pad appears equally adept at allowing you to control the expression on, for example, violins, trumpets and saxophone sounds, and it will be interesting to test these more critically in the full SOS review later this year.

Of course, the Z1's polyphony considerably extends the use of the Prophecy's models, allowing you (for example) to program a cracking harpsichord using the plucked string model. But what of the new, specifically polyphonic models? The first of these is the electric piano, and this offers imitations of the Wurlitzer EP200 and Fender Rhodes Stage 73, among others. Unlike sample‑based synths (which are limited by the nature and timbre of their source PCMs), the Z1 allows you to adjust parameters that relate to the physical nature of the original instruments. One example of this is the position of the 'pick‑up' with respect to the 'tine'. Changing this relationship creates a wide range of timbres and responses that conventional filters and ADSR‑type envelopes cannot imitate. This is because the complex harmonic structures and time‑domain responses of the sounds are significantly influenced by such factors. The Z1's electric piano model emulates these changes, making possible a far wider and more representative range of piano sounds.

Similarly, the Z1 incorporates an organ model that steps beyond conventional Sample + Synthesis methods. This allows you progressively to introduce or remove virtual tonewheel generators, just like pulling and pushing the drawbars of a genuine Hammond. There are limitations, but my first impression was one of 'grit' and considerable authenticity. This may, of course, be a consequence of Korg's Leslie effect algorithms (as found in the G4 and Trinity), so we'll have to investigate further.

The Z1 offers a Frequency Modulation model, although whether Korg will call this 'FM' in final production Z1s remains to be seen. (Korg named their last FM implementation 'VPM' — Variable Phase Modulation — for legal reasons.) Anyway, the FM model generates many of the bell‑like, percussive and piano‑type sounds that made the Yamaha DX7 such a world‑wide success. I find the use of DSPs to recreate earlier digital synthesizers peculiarly amusing, but it proves that the idea of a 'classic' synth is a flexible one, not limited to analogue instruments such as Moogs, ARPs and the Jupiter 8. Whether the concept is arcane or not, I'm looking forward to using this model more extensively. The DX7 suffered from appalling hiss, and the idea of noise‑free versions of its best sounds appeals greatly to me.

Finally, there's a bowed string model that complements its plucked counterpart. You can use this for orchestral strings or together with the analogue model for some luscious pads.

Once you have selected and programmed your models, you can pass the result through the Z1's effects processors. These, like those on the Trinity (and unlike those on almost any other manufacturer's synths), are multitimbral. This arrangement allows you, for example, to flange your guitar sounds while chorusing your pianos and independently EQ‑ing your bass, brass, and strings. The effects section is the Trinity's crowning glory, but far too few players appreciate its unique power and potential.

There are 15 'insert' effects, plus a master effects section that offers three further effects and a 2‑band EQ. Not as all‑encompassing as the Trinity's squillion effects options, this nevertheless remains streets ahead of the competition, and is another good reason to treat the Z1 as a very serious synthesizer.

And There's Plenty More...

The arpeggiator is a key element in the Z1's armoury, and it's another one that takes advantage of the instrument's polyphony. Arpeggiation can be monophonic or polyphonic, and you can choose its form from five pre‑programmed or 15 user‑definable modes that offer up to 36 steps each. The arpeggiator will act as a MIDI clock master, and you can therefore use it to drive MIDI sequencers and other clock‑sensitive devices. Most welcome, the Z1 transmits sequences over MIDI, making it possible to play arpeggios on synths that otherwise lack that capability. On the Z1 itself, you can limit arpeggios to individual parts and keyboard zones, allowing you to play other patches conventionally elsewhere on the keyboard.

Flam is another cool feature, and one that I've never before seen on a synth. Owners of Oberheim's Strummer or the Charlie Lab Digitar will be aware of the impressive results that you can obtain by strumming guitar patches or even non‑guitar sounds. Korg's implementation allows up and down motions on each arpeggiator beat, with the flam delay specified for each strum.

The Z1's four LFOs offer even more interesting possibilities, because you can lock each of these to MIDI clock, allowing a sound to have four in‑time modulations with durations ranging from breves to demi‑semi‑quaver triplets.

There is a Z1 editor that runs on PowerMacs and the later 680x0 Macintosh computers. This allows you to edit Programs, Multis, Global setups and Arpeggios, and it is also a powerful librarian for all things Z1‑ish. Editing is in real time, permitting you to twiddle virtual knobs while playing. Even the beta version I saw appears watertight, and the synth's output remains free from the zipper noise that plagued early digital editing systems. I found the editor invaluable for programming arpeggios, primarily because the Z1 offers too many facilities for anything less than a full‑screen editing display. If Korg don't bundle this software with the Z1, I'll give you their Managing Director's home address so that you can complain in person.


Are there any limitations to the Z1? Yes, of course there are. It falls far short of the original OASYS, it's not really designed for use as a primary instrument, and it lacks many sounds that you would expect from a top‑quality workstation. In particular, you mustn't expect acoustic piano emulations, because there aren't any.

Furthermore, the Z1 suffers from one of my pet hates: it's a multitimbral synth with just a single pair of outputs. I'll never understand why manufacturers think that two holes are enough, even if, like the Z1, the synth offers additional I/O in the form of an ADAT interface with a WordSync input. This, if you own an ADAT, is ideal, but I would prefer AES/EBU or S/PDIF interfaces. On the other hand, the ADAT's optical interface is becoming something of a standard for low‑cost multi‑channel digital I/O. It's economical to implement, it's reliable, and it can travel relatively long distances (especially when compared with S/PDIF). Since eight A/D converters or four AES/EBU outputs could push the Z1 over the £2000 barrier, I suspect that I should forgive Korg for choosing this configuration. Nevertheless, I still view the choice of ADAT I/O as a coup for Alesis' marketing department rather than as an ideal solution for multitrack recording.

Despite these problems (and a few others that will become apparent when we review the instrument in depth), and even without the control panels of the Roland JP8000 and Clavia Nord Lead, the Z1 may be irresistible. It costs just £200 more that its nearest rival, but offers superior 12‑note polyphony (an optional DSP expansion board will increase this to 18 voices) and 12 more physical models. Indeed, having played the pre‑production Z1 three times, I suspect that it's a significant step forward for polyphonic synthesis.

If you fancy an early view of the Z1 you may like to attend one of the dates on Korg's 'Digital Domain' tour. See page 18 in this month's news pages for details.