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Access Virus Indigo / Virus OS v4

By Gordon Reid
Published June 2001


Originally planned as a limited edition, the 37‑note Virus Indigo virtual analogue keyboard synth surprised even its makers — demand ran so high that it became a separate product. Gordon Reid considers the newest strain of this retro Virus, and the latest v4 OS software revision.

Ways not to start the day: 1) Find a leaking radiator flooding the floor behind a large, vintage — and probably irreplaceable — Yamaha synth. 2) Hear a nasty rattle when removing the Access Virus Indigo from its box, and disassemble it to remove the unattached screw lodged among the tracks and exposed connections on the keyboard decoder board. As Arthur Dent said in the original Hitchhikers' Guide To The Galaxy, "It must be Thursday. I never could get the hang of Thursdays."

Apart from the rattle, the thing I first noticed about the Indigo was its weight. I had no idea that its chassis and chunky aluminium (note to American readers: that's a word with two 'i's) end‑cheeks would be quite as substantial as they are. This may only be a three‑octave instrument, but it has the weight and presence of many five‑octave synths. This is good... flimsy is bad.

Before proceeding any further, I ought to explain that this is essentially two reviews in one: a look at the Indigo itself, and the v4 operating system that drives all the latest models of the Virus. So, for those of you unacquainted with the Virus family, I recommend a quick trip back to Sound On Sound's May 1998 and February 2000 issues (or" target="mainframe and" target="mainframe respectively), in which Paul Nagle reviewed the earlier original Virus (now known as the Virus a) and the later, still current Virus b and kb models. I'm not going to retread old ground here, and will concentrate on the differences between the Indigo and its siblings, and on the enhancements offered by the new operating system.

Beauty Is Skin Deep

Let's start by getting the hype out of the way. Access call the Indigo 'The Virtual Roadster'. I'm not sure what this is supposed to mean, but maybe they think it implies the open road, the sun in your hair, a beautiful woman gazing adoringly into your eyes as you sweep towards a horizon of endless possibilities... Oops, sorry. To me it means comfortable suspension and every mod con imaginable, and, for me, this is something the Indigo does not really deliver — as you will see.

The Virus Indigo's control panel, like those on the other Viruses, resembles a modern take on the Minimoog's classic layout. The big difference is the inclusion of an LCD and data‑entry keys to access those functions which have not been given their own physical knob or button.The Virus Indigo's control panel, like those on the other Viruses, resembles a modern take on the Minimoog's classic layout. The big difference is the inclusion of an LCD and data‑entry keys to access those functions which have not been given their own physical knob or button.

Nevertheless, it's worth taking a moment to admire the Indigo. In a world of conservative Japanese keyboards, and ghastly German/American synths that try to be stylish, but end up looking cheap and garish, the Indigo is a rarity — something unconventional that looks excellent. It's no bigger than a small '70s monosynth, but shares the clean‑cut good looks of the rare and lovely Akai VX600.

Unfortunately, there's a downside to the Indigo's compact design. Unlike on the Virus kb, the performance wheels are above, rather than alongside, the keyboard. I hated this layout on the Moog Rogue and the Crumar Bit One, and I still do. The Indigo's size has also prevented Access from enlarging the LCD. With so many keyboards now offering large, graphic displays, the provision of a 2 x 16‑character screen and the inevitable reliance on abbreviated parameter names is most unwelcome. Worse, the three‑octave velocity‑sensitive (but unweighted) keyboard feels cheap. I liked the keyboard on the Virus kb, so I have to ask why the Indigo's feels like such a step backwards. The Indigo also lacks the ability to generate channel pressure data, although it responds to it well enough. The Virus kb has aftertouch, so what are Access thinking of?

As for the keyboard length... in my opinion, 37 notes aren't enough on a monosynth, let alone a 16‑part multitimbral polysynth like the Indigo. On the other hand, a small synth is ideal for chucking into the back of the car to go to a mate's, or for grabbing a pair of headphones and hiding yourself away in the spare bedroom.

The OS v4 Upgrade

If, like most people, your last encounter with a Virus was somewhere in Version 3‑land, you'll find that v4 offers many additional benefits. For me, the most important of these are the new reverbs and improved delay effects. Although this isn't so important in the studio, I find keyboards without reverbs a real pain when I play live. This is because, whenever I need to use dedicated outboard effects (as opposed to simple FOambience) it doubles the number of cables in my rig, and significantly increases setup times.

The Virus Indigo's comprehensive I/O facilities: stereo analogue ins for external audio processing via the synth engine, three pairs of analogue audio outputs (four of which can be used to produce a quadrophonic output), MIDI In, Out and Thru, the headphone socket, and pedal inputs.The Virus Indigo's comprehensive I/O facilities: stereo analogue ins for external audio processing via the synth engine, three pairs of analogue audio outputs (four of which can be used to produce a quadrophonic output), MIDI In, Out and Thru, the headphone socket, and pedal inputs.

The reverbs themselves ('Ambience', 'Small Room', 'Large Room' and 'Hall') are more than acceptable, and you can program each of the algorithms in one of three modes: as a standard digital reverb, 'reverb+feedback1', and 'reverb+feedback2'. The last two of these are the same as having a delay line followed by a reverb; they treat the pre‑delay within the reverb algorithm as a repeating delay (which you can sync to the internal clock if desired) and then regenerate the reverberant effect for each of these repeats.

The delay is also great fun. This is not just because it offers numerous patterns, modulation, ping‑pong effects, and synchronisation to the master clock. It's because you can tweak the parameters in real‑time without generating digital glitching. I did this in the 1970s using a Pearl analogue delay, and it's a potent way to generate weird effects during performance. Set the feedback to maximum, play a few notes, and then sweep the delay time... it's hugely effective, and without artefacts. Oh yes, and while on the subject of effects, v4 offers an additional saturation stage as well as distortion and a range of grungy 'lo‑fi' effects. Nice!

On the other hand, Access claim that the Virus now offers up to 82 simultaneous effects, but this doesn't stand up to scrutiny. Sure, five effects are available on a 'per‑part' basis, and with up to 16‑part multitimbrality, this suggests that 80 is the correct number. But look at the effects list... 'Ring Modulator', 'Distortion', 'Analogue Boost', 'Phaser', 'Chorus'. When did you last see a ring modulator described as an effect? In my opinion, that's part of the voice structure, as is 'Boost'. That leaves the distortion, phaser, and chorus. Hang on... where is the reverb/delay? Well, this is only available as a master effect applied to an entire Multi. That's right... there's just one of 'em, no matter how multitimbral you are trying to be. This is more Waldorf Q than Novation Supernova, and very disappointing given the quality of the effects. Nonetheless, it's an inevitable consequence of the Virus's single 56303 processor. To paraphrase a cliché: you can't pour a quart from a pint pot.

The arpeggiator in v4 is a huge leap forward from the rather mundane implementation in previous OS versions. There are now 40 rhythmic patterns that you can apply to the six arpeggio modes: 'up', 'down', 'up and down', 'as played', 'random', and 'chord'. There's also a Swing parameter that does as you would expect, with all timings referenced to the synth's master clock. Unfortunately, the Indigo has no front‑panel controls for the arpeggiator: no latch switch, no rate knob... nothing! I thought that this was a bit naff on the original Virus a and, with all the additional capabilities of v4, it's doubly so.

Moving on, v4 now lets you process incoming audio through the Indigo's effects section without using up polyphony. This makes the synth a powerful stand‑alone audio processor, with up to seven simultaneous effects in series. If you want to mutilate your audio even further, you can pass it down the internal signal chain, through the filters, overdrives, and envelopes, even gating it with the arpeggiator to chop it up into unrecognisable little chunks. Whatever turns you on, I guess.

There are no radical changes in the voicing, but Access have added three more things that make v4 sexier than earlier Viruses. The first of these is a random patch generator. This offers two parameters; one to determine how many parameters will be changed, and another to limit the amount by which the generator is allowed to affect them. Used with restraint, this can create interesting results, but when given free reign... it's fun, but in many hours of pressing the button, I didn't once create a patch that I considered worth saving.

The next upgrade is, for me, more interesting, because it creates genuinely new synthesis possibilities. It's a Surround capability that allows you to position the sound in a quadraphonic space. You can distribute a signal between four of the six outputs, panning it left/right and front/back in real time. You can even modulate this to send the audio swirling around your head in ways that The Moody Blues and Keith Emerson could only dream about in the '70s.

Finally, Access have added sound categories to the Virus. You can allocate two out of 16 such categories to every patch. Then, using the Find command, you can search for patches within these classes. Unfortunately, you can't define your own category names, so the facility is of annoyingly limited use.

Wish List

I first encountered the original Virus back in 1998, and I was very impressed with its sound. Indeed, my thoughts at the time were that analogue die‑hards should be sent to their bedrooms and only allowed out when they had had time to reconsider their anti‑DSP prejudices. The Indigo does nothing to change my view, and I would challenge anyone to spot its digital heritage in a mix, unless I was intentionally creating sounds of a digital nature.

Sadly, the factory sounds do nothing to demonstrate the breadth of the Indigo's capabilities. I found little that stepped beyond dreamy, ethereal pads or the limited, and limiting, sounds of hardcore techno, industrial and trance. What's more, the arpeggiated patches are becoming clichés in their own lifetimes. So here's the first item on my wish‑list: voice programmers with a bit of imagination who can demonstrate this instrument's huge range of sonic capabilities.

There are also several areas in which the Viruses themselves could be improved. For example, the filters will not self‑oscillate without input from the oscillators. Sure, all filters need a small kick to get them going, but it should not be necessary to have a permanent input driving them.

I would also love to see more waveshapes on board. I've long been a fan of the PPG Wave, and sweeping through the Virus's existing 64 waves can be very gratifying. OK, so I'm converting the Virus from a Virtual Analogue to a Virtual Wavetable Synth, but why not? The Waldorf Q does this, albeit in limited fashion.

On the functional side, the Virus could still do with a handful of tweaks. For example, there's still no way to copy effects from one patch to another, and — notwithstanding the limitations of the reverbs/delays — this can be a real pain when trying to recreate a Single within a Multi. Furthermore, it's all very well having 32 modulation sources and 97 destinations, but you need more than three source and six destination slots in the onboard modulation matrix if you're going to take full advantage of this.

I also want another manual. Not to augment this one, but to replace it. It tries to be clear and instructive, but with no index, no block diagrams, and no specifications, it's more trouble than it's worth.

But now for the biggie... Given the number and importance of the software upgrades to the Virus' OS over the past two years, I think that Access should have taken the opportunity to redesign the Indigo's front panel in a much more significant fashion. I'm not complaining about the clearer graphics and the improved panel hardware, but why not find room to give the third oscillator and arpeggiator their own controls (they're still buried in a menu), and bring some of the effects to the front? Sure, you would need a bigger panel, but I'm not a fan of the Indigo's size, anyway. Imagine how much better it would be with a 61‑note keyboard, and a comprehensive control panel. Virus Pro, anybody?


This software upgrade incorporates several improvements that have been on owners' wish‑lists since the launch of the original Virus in 1998 (and more improvements are on the way — see the 'Software Support & Upgrades' box elsewhere in this article). For me, the reverbs and the enhanced delay algorithms are the most important of these, and they make an already first‑class synth sound better than ever. Nevertheless, I can see that random patch‑generation, the sound categories, and the improved arpeggiator are going to be just as attractive to many people. Other upgrades such as the lo‑fi effects, the improved processing of external signals, and the pattern delays are aimed squarely at modern dance music, and bring the Virus more into line with competitors such as the Supernova II. Some people may bemoan the lack of a step sequencer, but I'm not one of them. I'm pleased that Access have concentrated on producing an excellent OS with so few bugs.

Now let's consider the Indigo... That it's super‑cute, sexy, and will appeal to players for whom style is a major attraction is without question. That — from a traditional keyboard player's point of view — its cheapo three‑octave keyboard is about as useful as a one‑string guitar is also without question. So let's accept that you're unlikely to see Vladimir Ashkenazy, Oscar Petersen, or even Tony Banks playing one, and admit that there are many other ways that synths are used in 2001. As a compact sound effects generator on a small stage, as a sound source and signal processor in a tiny studio, or in any other discipline where piano‑style playing is not required, the Indigo's amputated design could be a benefit rather than a hindrance.

But despite trying to maintain these positive thoughts, I soon found myself treating the Indigo like the Nord Modular Keyboard. I occasionally used the Clavia's itsy‑bitsy keyboard when programming, but always played it via MIDI from a 76‑note, pressure‑sensitive Roland JV1000 or Trinity Pro. Why? Because the Indigo sounds great, and it deserves to be played across a much wider range than its own hardware permits. Furthermore, the Trinity's ribbon controller offers many possibilities that the Indigo can't provide.

Of course, using the Indigo in this way demotes it to the role of a sound module, so you may be tempted to ignore it altogether and wait for the forthcoming Virus Rack. Unfortunately, it is already clear from Access' advance publicity that the sound engine in the Rack is significantly inferior to that in the Indigo (see the 'Other Modules' box elsewhere in this article). Consequently, pose‑value and flashing blue LEDs notwithstanding, I can't help feeling that — provided you have the space — you would be better off with a Virus kb, or a Virus b hooked up to the controller keyboard of your choice.

Now, I wonder where that screw came from?

Software Support & Upgrades


Access provide two flavours of Virus editor via Emagic's SoundDiver editor/librarian software. Firstly, there's a free plug‑in for all registered owners of the full version of SoundDiver (v3.0.1 or later). This supports Virus OS v4.00 and above. The editor isn't bug‑free, but a new revision is in the works, and everything should be sorted out soon. Secondly, the company has just announced a low‑cost OEM version of SoundDiver that edits only Viruses, and should be available by the time you read this.

  • OS V4.02

On 15 January 2001, Virus OS v4 reached v4.02, which fixes a number of bugs in v4.00 and adds a couple of minor features. You can download it from the Access web site, and it should be compatible with any Virus b, Virus kb, or Indigo. Some users have complained that the 233K v4‑to‑v4.02 upgrade file is problematic, but a 'clean install' seems to cure the problems. OK, so this requires a 3.7Mb download, but isn't it better to be safe than sorry?

Note that the original Virus a cannot use OS v4 in any of its forms. However, in March 2001, Access announced what they claim will be the final revision of the operating system for the Virus a. This is OS v2.8, and it should be available by the time you read this. The new version will include the Indigo's Analogue Boost effect, the improved arpeggiator, sound categories, and the random patch generator.

Apologies From Access

In a curious and possibly unprecedented move, Access' CEO, Christoph Kemper, has apologised on the Access web site for the late delivery of the Indigo. He attributes this, in part, to a level of demand that, he says, is far greater than expected. It appears that Access thought that the Indigo would be a Special Edition, whereas the public has taken it to its heart and made it a mainstream product. This must be frustrating for Access, because there's a lot of extra cost and work in those side panels and the improved hardware. Maybe that explains why the Indigo costs almost as much in the UK (and exactly the same in the US) as the full‑size Virus kb...

Other Hardware & Software Modules

The Virus Rack should be with us soon. The bad news is that this will offer 16 voices rather than 24, and eight‑part multitimbrality rather than 16. It also loses the Indigo's third oscillator and several of its effects, including the phaser, distortion, and surround capabilties. The good news is that Access have undertaken to develop a hardware upgrade to allow the Rack to run v4. Why the company would announce this before releasing a hamstrung version is beyond me.

In addition, if you have a Digidesign Pro Tools TDM system, you can now buy a 'virtual' Virus plug‑in. This too offers just 16 voices per DSP chip in your Pro Tools system, although you can use multiple chips to run more voices. However, like the forthcoming Rack hardware, the TDM version offers only eight‑part multitimbrality, no reverb, no phaser, no distortion, and no surround capabilities. Furthermore, it does not appear that there will ever be an upgrade to OS v4, so if you want the new operating system, you'll still have to buy one of the physical versions of the synth.

Brief Spec


  • Polyphony: 24 notes maximum.
  • Multitimbrality: 16 parts.
  • Oscillators per voice: Three plus sub‑oscillator.
  • Analogue‑style waveforms: saw, pulse, sine, triangle (all with pulse‑width modulation).
  • Spectral waveforms: 62.
  • FM: Two‑operator.
  • Filters per voice: Two.
  • Filter modes: Low‑pass, high‑pass, band‑pass, band‑reject.
  • Filter routings: Four.
  • Maximum filter cutoff slope: 36dB/octave.
  • LFOs per voice: Three.
  • LFO waveforms: 68.
  • Maximum number of mod‑matrix routings: 6.
  • Mod matrix sources: 32.
  • Mod matrix destinations: 116.
  • Other modulation routings: Assignable for LFO1 and LFO2, plus fixed routings.
  • Envelopes per voice: Two.
  • Envelope: ADSTR (T=Time).


  • Arpeggiators: 1 per program (up to 16).
  • Maximum simultaneous 'insert effects': five per voice (but see text for restrictions).
  • Master effects: Delay/reverb.


  • Programs: 512 (in four banks of 128).
  • ROM preset programs: 256.
  • RAM program memories: 256.
  • Multis: 128.


  • Analogue signal inputs: Two.
  • Resolution of inputs: 18‑bit.
  • Analogue signal outputs: Six.
  • Resolution of outputs: 24‑bit.
  • Calculation depth: 24‑bit.
  • Sampling rate: Not specified.


  • Size: 54 x 34 x 11.5cm.
  • Weight: 7.5kg.


  • Thanks to OS v4, the Virus now sounds better than ever.
  • OS v4.02 (the latest) is glitch‑free.
  • High‑quality reverbs and delays.
  • Quad surround capability.
  • Improved arpeggiators in OS v4.
  • The Indigo itself is built like a Panzer tank... a sexy Panzer tank!


  • The Indigo's unweighted keyboard feels cheap, and there's no aftertouch except over MIDI.
  • The keyboard will be too short for many players.
  • Reverb/delays not multitimbral.
  • The manual is poorly organised, with no index.


The v4 Virus (in all its forms) is almost a classic synth. Indeed, with a handful more hardware and software updates it could be the best analogue‑style synth on the market. The Indigo is an interesting new slant on the style and form of powerful modern synthesis — sure to appeal to some players, but unsuitable for others.

Published June 2001