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Prophecy Fulfilled

Prophet VS

Is Vector Synthesis the answer to every programmer's prayers, or another technological blind alley getting in the way of music? Peter Schlesinger takes a long hard look at the digital Prophet.

After previewing Sequential's first digital synthesiser two months ago, we take a trip to the company's California HQ to find out what it's really like. Our findings are conclusive: Vector Synthesis is a winner.

Some simple but appetite-whetting press releases, a couple of all-too-brief trade show demonstrations, an advert or two, and some natty blue and black casework. That was all I'd seen of the Prophet VS, up until a recent visit to Sequential's closely-guarded California headquarters. It had been enough to get my mind racing as to what the new machine might be capable of, but in retrospect, it did little to prepare me for the sheer size of the leap between the VS and every other 'affordable' polyphonic synthesiser you care to name.

Four oscillators per voice to start with (even Moog, in their heyday, only ever got up to three), and separate envelopes for volume, filter and oscillator mix. Useful additions to the synth player's arsenal, even if they weren't accompanied by major innovations. But they are.

Most obvious of the innovations is the joystick, not a newcomer to synth ergonomics by any means (Korg have been using them for years), but in this incarnation, a vital new tool that allows an unprecedented degree of real-time control over harmonic content, during both performance and programming. In the latter, you use it to adjust the mix between the four oscillators, either for creating new waveforms, or for defining the five possible levels in the new Prophet's 12-parameter envelopes. And if those envelopes aren't comprehensive enough, any portion can be repeated a fixed number of times or continuously.

A host of other niceties is available onboard the VS, including what must be the most sophisticated arpeggiator ever seen on a synth (more on that later). But before discussing these, it would be churlish not to describe the way the VS goes about generating sound.

Vector is a term borrowed from Cartesian mathematics, and is used to describe a line not just in terms of length, but also with reference to the position of its start and end points. These would normally be specified as x-y co-ordinates, and the length and direction of the vector is deduced by subtracting the end co-ordinates from those of the start.

What has all this got to do with synthesis? The connection comes from the fact that there are four sound sources to be mixed together in real time, while notes are sounding. Ordinarily, mixing two synth oscillators together is easily accomplished using a balance knob or lever, so achieving a mix of four oscillators is simply a matter of splitting the task into two groups using two levers. Or is it? Not really. You still need some way to control the relative mix between the two groups, and this can be accomplished by mounting the two levers on different axes of the same device, so that two separate parameters can be altered interactively, as it were. Korg have been fitting a control for this purpose for years, as an alternative to the two wheels that most manufacturers use for pitch and mod control. It's called a joystick, and computer-game addicts will probably be intimately acquainted with its advantages: you can move in two dimensions when the aliens are after you. Well, there are no extra-terrestrials lurking inside the VS (though some of the sounds have an unearthly quality), but the principle is the same. Using a joystick, you have complete control over the levels of four oscillators simultaneously. This is done by placing one oscillator at each corner of the diamond-shape through which the joystick moves. These are labelled A, B, C and D in the west, north, east and south corners respectively. When the joystick is pushed hard up against any corner, you hear only one oscillator. In any other position, you hear a mix based on the distance the joystick is from each oscillator's corner. The nearer it is to a particular corner, the louder that particular oscillator sounds.

What's more, the position of the joystick can be used to mark the start and end points of transitions between one mix and another. This is how the mix envelope is programmed, as we'll see later on. First, though, let's look at the waveforms each oscillator can generate.

The VS comes with 128 waveform storage locations, of which 96 are factory preset and 32 can be over-written by the user. The first and last of the factory presets are old friends - sinewave and white noise - so you won't be completely at a loss.

More traditional, harmonically satisfying waveforms like sawtooth and pulse shapes are also offered, but all waveforms are identified solely by a number, so you need to be able to recognise the sound of traditional waveshapes if you want to use them. This may sound a bit silly, but the manual rightly points out that 'as they were created and are edited by ear, there is no point attempting to discuss the specific harmonic content of the ROM waveforms'. This refers primarily to waveforms whose shape cannot be conveniently described by such colourful terms as Sawtooth and Square, but in my view, there's no harm in approaching all the factory preset waveforms without the preconceptions imposed by names.

Amongst my own favourites are some wonderfully spikey-sounding numbers, reminiscent of the sort of thing you'd normally need Sync or Ring Mod to achieve, as well as mellower-sounding shapes for people who don't have my taste for the filthier, more distorted side of synthesised life. There are plenty of good starting points for strings and brass sounds; and as it turns out, the filtered string factory preset is possibly the most beautiful synthetic string sound I have ever heard.

More intriguing than all this, however, are the waveforms that allow you to create sounds which don't fall into conventional musical categories; waveforms with harmonic contents that aren't possible to create using analogue or FM techniques. No reasonably-priced synth has ever offered such a wide range of waveforms as a starting point for sound-generation. And the best news of all is that this process is very quick and easy to use, and the results can be heard in real-time (ie. as you make the changes).

This is how you actually go about creating your own custom waveforms. Using the Oscillator Select switch to cycle round the four oscillators, assign each one a Wave Number and a harmonic multiplier which doubles, trebles, or quadruples (and so on, the choice is yours) the fundamental frequency.

Joystick position on VS front panel is used to specify five mix envelope stages, as well as balancing between four oscillator waveshapes, all in real time

Now comes the difficult bit. Grasp the joystick firmly between thumb and forefinger, and move it about until you hear something you like. Now press Store and, miracle of miracles, you've just created your own unique waveform.

This delightfully straightforward process belies its own flexibility. In reality, there are several ways of using this procedure to create sounds that are individual to you.

If you feel additive synthesis represents the ultimate in terms of purity of method, assign a sinewave to all four oscillators, giving each a different harmonic number. Then you can vary the levels of all four harmonics (choose from any between the fundamental and the 32nd harmonic) using the joystick, and hear the results as you go. Because the four oscillators are independently controlled, the VS' processor doesn't need to compute the waveform each time a change in relative levels is made. Thus the VS' additive synthesis capacity is more instantly accessible than those of mortgage-priced systems like the Fairlight, though it must be stressed that the Prophet can only deal with a maximum of four harmonic levels simultaneously. To add progressively more harmonics, you simply save the combination of the first four in one of the user locations, and then, in the next stage of editing, place that waveform on one of the oscillators and use the other three to bring new sinewave harmonics into play. This process can be repeated any number of times to build up as complex a sound as you like.

If you haven't the stamina to build up everything from scratch like this, fear not: you can take a shortcut by using the joystick to select four different wave numbers, any of which can be either preset or user-programmed. In this way, you can take advantage of complex waveforms that have been created in advance, and quickly combine them into a new waveform. Programming buffs will readily appreciate just how easy it is to spend hours fiddling with the VS joystick, learning about how sound is made up and, with luck, creating some interesting synth voices in the process.

When you've finally selected the four waveforms you want to use (decisions, decisions), you can use the joystick as a performance control to mix them together while you're playing. Alternatively, if you don't fancy yourself as one of the new generation of synth-playing virtuosi, you can control the respective levels via the mix envelope. Setting the varying levels of four oscillators could have been quite a long-winded procedure, but fortunately, Sequential have managed to press the joystick into service here, too. All you do is waggle the joystick to set the mix you want at each stage of the envelope, whilst playing the keyboard to hear how the harmonic content changes through time.

If setting five distinct mixes to occur during the course of a note isn't enough, you simply invoke the next Sequential innovation - looping envelopes. All you have to do is select the envelope stages that you want to loop between, choose the desired looping mode - forwards or backwards/forwards- and away you go.

Essentially, looping envelopes can be seen as programmable LFOs which give you the ability to define specific and complex waveshapes to control your modulations.

And these 'custom LFOs' can also be used to govern the VS' more standard analogue components, like the Filter and Amplifier sections. The accompanying illustration shows how the various looping options affect the resulting envelope-LFO hybrid.

To cure old-timers' moans about mercurial digital synthesisers not having good old analogue filter sections on the end of them, Sequential have provided each VS voice with a Curtis filter that will sound very familiar to anyone who's spent any time at all with the Prophet 5 and its relatives.

Using the new Prophet simply as an old-fashioned four-oscillator synth running through a butch four-pole filter, you can make sounds which put old standard analogue polys from the likes of Moog, Oberheim and even the old-look SCI in the shade: punchy synthetic brass and silky, sweeping strings can be quickly conjured from the VS, with all the warmth and depth you'd expect from a high-ticket analogue synth.

The conventional ADSR envelopes normally associated with the better analogues have been expanded to the same 12-parameter, five-stage versions which the mix envelope uses, but don't worry: standard ADSR shapes are easily produced.

But the most exciting aspect of the VS is the sounds you start to obtain when you make both the analogue and digital sections of the instrument work for their living. Get four interesting sounds up on the oscillators, create a dynamic mix of them using the joystick to set up the mix envelope, stick a nice bold filter-sweep on top, and you've got the best of both worlds. I couldn't leave it alone...

Envelope looping is affected by setting different loop stages and directions

In addition to all this, a wide variety of modulation options lies within the VS' configuration: two LFOs, velocity, pressure, keyboard track and mod wheels can be routed to control almost everything on the machine from pitch and filter cutoff through mix and amp levels to stereo panning and chorusing. The number of possible combinations of sources and destinations produced is enough to keep any self-respecting synth programmer in transports of delight for at least a couple of months (doesn't sound like enough to me - Ed).

All I can really do, in the space available here, is give you a taste of what's available by looking at a few of the more instantly appealing configurations.

To start with, stereo positioning. This is one of the new territories which the VS explores for the first time. Each patch can hold its own stereo setup, which can range from a split patch being sent left and right, to spectacular auto-panning effects-though with a much finer degree of positional control. You can, for example, specify a pan position for the sound to start at, and then use an LFO or the filter envelope to move it around that mean position. Or you can use additional keyboard pressure to suddenly move everything to the left. Or use keyboard position to place the sound in a more 'natural' stereo spread.

These stereo facilities come into their own during live performance, and although their studio usefulness is limited by the fact that most stereo instruments are ordinarily shoved through two separate input channels on the mixing desk, their complex assignment possibilities ensure they never become redundant.

The Prophet's built-in chorus unit has programmable depth and rate parameters, and both of the latter can be controlled from things like the mod wheel and pressure-sensitivity - very expressive. That's as far as the section goes, though, which is a bit disappointing when you consider Korg are putting a fully-fledged, patch-programmable DDL inside the Poly 800II, which sells for just over a quarter of the VS' price.

When you've finally stored your patch, you can combine it with other patches in several ways. To access two programs simultaneously, you have to 'Link' them together. When you've done this, you can decide whether you want to use the two programs in a Split or Double format. The Split mode is fairly straightforward, but Double has a couple of nice features that represent an extension of the Stack mode on the Prophet 2000. You can detune the secondary or Linked program from the first by a certain number of cents, or delay the Linked program by a certain number of milliseconds. The most obvious use for this is Linking a program to itself, to provide further fattening-up or echo effects respectively; but why limit yourself to the obvious?

Sequential more or less invented MIDI, so you'd expect the VS to be well-equipped on that score. It is. Apart from standard facilities like MIDI clock, pressure, program-change and so on, the MIDI feature to look out for is the VS' ability to receive small quantities of sample data from the Prophet 2000, or any other sampler which implements the MIDI sample dump spec agreed last year. Now, before you get all excited that the VS can play samples too, I'd better tell you that the length of sample it can accept is only 128 words. However, by sampling the correct pitches (which the VS manual tells you how to do), you can extract a single waveform from a sample and use that as one of the VS oscillators. Potentially, any audible waveform could therefore act as a source for new sounds on the VS. And it almost goes without saying that you dump programs and wave data out via MIDI, so the process can work both ways.

Finally on the MIDI front, the arpeggiator recognises and sends all sorts of goodies via MIDI.

Looking back over this review, it's clear that in the course of all this waxing lyrical, I've omitted to mention some of the fundamental facts of the VS' spec sheet. You'll find most of these covered in the accompanying Datafile, but the rather unusual nature of this review does, I think, reflect the extraordinary nature of the VS, an instrument whose innovations are so numerous, they distract you from answering the standard 'how many programs has it got?' and 'how good a brass sound can it produce?' queries that synth players ask so often.

As for comparisons, putting the VS next to most other synths in its price range and trying to make a judgement would belittle its flexibility. Yes, I heard sounds which could have been made by a DX7. Yes, I heard sounds which could have been a PPG. Yes, I heard sounds which could have been a Prophet 5. But more important, I heard sounds I've never heard before, and manipulated them quickly and easily.

In a world where the sampling keyboard can capture any sound that has already been recorded somewhere, what we desperately need is a keyboard that can help us find new sounds. I think the VS is it.


Sequential VS Vector Polysynth

Keyboard 61-note, C-to-C, weighted keys, velocity and pressure sensitive

Sound Source 4 oscillators per voice, generated in software, manipulated using Vector Synthesis

Voicing 8-voice polyphonic; Single, Link, Split and Double Modes (with Unison option)

Memory 100 RAM memories for user-programmed sounds, shipped containing 100 factory presets; 96 ROM waveform (preset) and 32 RAM waveform (user-programmable) storage locations

External storage Cartridges: VSRAM (Model 240), 100 RAM memories and 32 RAM waveform locations; VSROM (Model 241), 100 ROM memories

Display 32-character LCD

Interfacing Left and Right audio outs; Alternate Release footswitch (piano-type sustain, etc); Aux footswitch (Arpeggiator Latch); MIDI In, Out & Out/Thru

Price RRP £1899 including VAT

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Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.


Electronics & Music Maker - May 1986

Donated & scanned by: Stewart Lawler

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