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Arturia OB-Xa V

Software Synthesizer By Gordon Reid
Published August 2020

Arturia OB-Xa V

Arturia's latest instrument is a software recreation of Oberheim's pinstriped polysynth.

Arturia's V series of virtual instruments started in 2004 with Minimoog V, and this was followed by emulations of classics such as the ARP 2600, Roland Jupiter 8 and Yamaha CS80. In those early days, the company sometimes got it right and sometimes less so, but by the time that they released last year's V Collection 7, there was no longer any question that their software could successfully emulate a long list of cherished instruments. I've reviewed many of these, but it always seemed to me that two of the greats were missing: the Memorymoog and something from the Oberheim OB‑series. But today, half of that has been corrected.

The Technology

There would have been little point in modelling the earliest of the OBs, the OB‑X, because it was closely related to the 4-Voice and 8-Voice, and that territory has already been covered in large part by Arturia's SEM V. (See the 'A Bit Of OB History' box.) However, I was a little surprised to find that Arturia chose the OB‑Xa as the basis for their OB‑series soft synth. Perhaps that was a marketing decision; for reasons that escape me, the OB‑Xa has always had a better reputation than the OB‑8. But while Arturia may have chosen the OB‑Xa name, they haven't stuck to the OB‑Xa architecture. Indeed, OB‑Xa V might more properly have been called OB‑X/Xa/8 V, although that would be a lousy name for a product.

You can immediately see the differences between the original OB‑Xa and the soft synth when you compare their oscillator sections. Whereas the original offered just sawtooth, pulse (with PWM) and saw+pulse wave options, the soft synth adds the triangle wave of the OB‑8, which is a sensible and useful addition. You'll also find a cross modulation (X-Mod) knob sitting between the oscillators. Cross-mod was one of the main features of the OB‑X, but was dropped by Oberheim on the OB‑Xa, so it's great to see it reinstated here, especially since you can now determine the amount of modulation. And, while it appears that the OB‑Xa's ability to sweep the pitch of Osc 2 using the filter envelope has been lost, this is easily programmed in the soft synth's modulation matrix. Another change lies in Arturia's repositioning of Osc 2's fine-tuning control. They have moved it from the Control section to the Oscillators section, which is a more significant modification than at first it seems.

Further differences are apparent in the filter section. On the OB‑Xa, there were six possible oscillator mixes: Osc 1 could be off (0 percent) or on (100 percent), and Osc 2 could be off (0 percent), half (50 percent) or full (100 percent). In addition, noise could only be on or off. Arturia have sensibly replaced all of these buttons with variable amplitude controls for both the oscillators and the noise. The rest of the filter section is common with both the OB‑Xa and the OB‑8, with knobs for cutoff frequency, resonance and modulation amount (actually contour amount), plus switches for the 12dB/oct and 24dB/oct modes and 100 percent keyboard tracking on/off. (Other tracking rates can be programmed in the modulation matrix.) The filters on the original synths never quite oscillated in either mode, but the resonant peak seems a little more pronounced on the soft synth and that's no bad thing.

All OBs had two ADSR contour generators, and these are reproduced here. They weren't the snappiest in the world and, at their minimum settings, those on the soft synth are considerably faster; if you want to achieve the same 'spit' as you obtained on the original, you have to slow the soft synth down a little.

The modulation window offers modulation capabilities far in excess of what was possible in 1983.The modulation window offers modulation capabilities far in excess of what was possible in 1983.

Like much else here, the OB‑Xa V's modulation section is inspired by the OB‑8 rather than the OB‑Xa, offering an LFO with seven waveform options, key synchronisation and MIDI sync. You can direct the output from this to the oscillators' pitches and the filter's cutoff frequency with one depth, and to the oscillators' pulse widths and the amplifier gain with a second.

The OB‑Xa also had a dedicated vibrato LFO in its performance panel. This offered sine, sawtooth and square waveforms with a frequency range of approximately 0.1Hz to 20Hz, and you could direct it to the pitches of Osc 1, Osc 2 or both, with the depth controlled by the modulation paddle. This LFO (now with a range of 0.063 - 13.5 Hz) has moved to the main panel, as has the OB‑8's arpeggiator which, as well as adding clock sync, now has two extra modes and a huge range of up to six octaves.

Moving on, the Voices panel looks simple, but is one of the soft synth's most powerful features. On the original, the Control section (which is its equivalent) allowed you to apply portamento, detune Osc 2 against Osc 1, and put the synth into a single eight-voice unison mode. On the soft synth, portamento is given in its own panel but remains constrained to the OB‑Xa's limited capabilities with just time and glide/glissando options. (I'm quite surprised that in this case Arturia didn't adopt the OB‑8's architecture, which would have given the instrument linear and exponential curves, equal-rate and equal-time modes, legato and polyphonic modes, and glide and glissando modes.) However, the Osc 2 Detune knob (which, as already mentioned, has been moved to the Oscillators panel) has been replaced by a Unison detune knob. You can choose the number of voices in a Unison stack and obtain some enormous sounds — both monophonic and polyphonic — but there are only 16 voices in total, so you have to balance your desires against what is feasible.

This is far from the limit of this section's ability to thicken the sound. Activating the Stereo option and increasing the Spread from zero causes two slightly different voices to be generated in the left and right channels. It puts a heavy load on the processor, but it's much more vibrant than chorusing. What's more, activating this also allows you pop open a hidden panel to reveal an additional set of controls that determine the maximum amount of detune, filter cutoff frequency offset and LFO phase offset between the two copies.

There's no need to charge up your electric screwdriver to adjust the pan positions of the voices.There's no need to charge up your electric screwdriver to adjust the pan positions of the voices.And yet more... there's an additional LFO here that sweeps the pan of each of the copies. This is powerful stuff and can create some wonderful sounds. Alternatively, you can select the Pan option to reveal a second panel containing images of eight screws. These mimic the pan adjustment screws found inside the OB‑Xa and which poked out of the side of the OB‑8. The Spread knob then controls the maximum width.

Finally, the Master section contains a Hold function, plus a button called Sel that allows you to program the chord that's played on every note if the Chord button is activated. In addition to its obvious use, this is a great way to program multi-pitched sounds that you can't obtain from just two oscillators per note.

Beyond The OBs

Looking at OB‑Xa V, there's no hint of the OB‑8's Page 2 parameters which included the ability to quantise the LFOs and choose phase offsets, LFO inversion and key synchronisation, bipolar delay/attack contours for the LFO depths, LFO keyboard tracking, programmable sustain pedal release times and more. Happily, even more facilities (although not all of the OB‑8's) are available through the modulation/effects panel that pops up above the main control panel when asked to do so.

You can insert your choice of effects into three slots to spice up your patches.You can insert your choice of effects into three slots to spice up your patches.

Turning first to the modulation panel, this contains two sections: a four-slot 'function generator' and a small modulation matrix. You can create complex multi-stage curves in each of the function slots, with each stage offering definable concave/linear/convex responses, and then direct the curve to any one of 50 destinations that include all of the major synthesis parameters as well as some of the modulation and effects parameters. With options for key triggering, looping, monophonic or polyphonic output and various sync options, you can use the function generators as LFOs, step sequencers, and contour generators that go way beyond what is possible with ADSRs. Next to these, the 5x6 matrix offers five fixed sources (velocity, the note number, aftertouch, the mod wheel and the filter contour) and you can direct six instances of each of these to your choices from the same list of 50 destinations. I can't stress the value of this matrix enough because this is where OB‑Xa V really comes alive. With up to six destinations of your choice for each of velocity and aftertouch, each with individual amounts and polarities, it makes the soft synth the Oberheim that you always dreamed about. My OB‑8 is wonderful, but the ability to emulate it and then add all manner of expression when performing is even more so.

A hidden panel allows you to program a rich stereo soundscape for any sound.A hidden panel allows you to program a rich stereo soundscape for any sound.Switching to the effects section, this offers three slots into which you can pop your choices from nine effects options. These are a reverb, a delay with a maximum feedback gain of 100 percent for infinite delays and sci-fi effects, a stereo chorus offering 1, 2 or 3 delay lines, a flanger, a stereo 2, 4, 6, 8, 10 or 12-pole phaser, an overdrive, a compressor, a bit crusher that can create distorted aliasing mayhem, and a resonant multimode filter. All of these offer a good selection of parameters and, while they're not the most refined or sophisticated effects in the world, there's still a lot to like here.

The soft synth's other facilities are much as we've come to expect from Arturia. For example, you can scale the GUI from 50 to 200 percent to best suit your working space, and the extensive patch management system organises your sounds according to authors, banks, types and characteristics as well as providing a field to add text notes to each. It also allows you to create playlists, and to export and import patches and banks of patches.

I was also delighted to find an extensive Undo/Redo facility. The value of this became clear after I spent considerable time modifying a favourite sound and then saved the new version on top of the original. Much swearing might have resulted, except that I was then able to Undo back to the starting point and re-save the original with a modified name. Nice!

At this point, you may have noticed that two key features are missing from OB‑Xa V. Both the OB‑Xa and OB‑8 could split and layer two patches, and there were even 12 split memories and 12 double (layer) memories provided in addition to the 120 patch memories. If you're running the soft synth as a plug‑in, emulating these splits and layers is straightforward; if your host system has the power, you can launch two instances and allocate them to different MIDI channels and play them as required (split) or to the same MIDI channel (layer). But you can't do this when using the stand-alone version because only one instance can be run at a time, which is a significant shortcoming.

In many ways, Van Halen's 'Jump' was the worst thing ever to happen to an Oberheim...

In Use

I don't know whether anyone understands precisely why the OB‑Xa is so recognisable. There's nothing unusual about its architecture, and it used the same oscillator and filter chips as some of its rivals. But for whatever reason, the CEM VCOs and VCFs in the OB‑Xa and OB‑8 sounded different from the same combination of chips in, say, later Prophet 5s and the Prophet 10. To be fair, you could program Oberheims and Prophets to sound almost identical if you kept things simple, but if you pushed them beyond basic patches, they soon entered different sonic territories. And so it is here. But that doesn't answer the key question; can OB‑Xa V sound like an OB‑Xa? In short, yes, it can... often remarkably so. Of course, someone is bound to declaim that all of this is irrelevant because "the OB‑X sounds far better than the OB‑Xa and OB‑8 and you must be deaf or stupid to like the later models", an opinion often proffered by people who have never owned either. But the OB‑X was quite limited in what it could do well, whereas the OB‑Xa and, in particular, the OB‑8 had a far wider palette. With its fusion of OB‑X, OB‑Xa and OB‑8 capabilities, OB‑Xa V is much more flexible and powerful than any of the originals and, if you want something closer to the SEM-derived sound of the OB‑X, you can always launch SEM V instead.

The colour scheme isn't haute couture, but it certainly lets you see which controls are assigned to MIDI CCs and which are not.The colour scheme isn't haute couture, but it certainly lets you see which controls are assigned to MIDI CCs and which are not.

Nonetheless, not everything is rosy. On occasions it took me a lot of work to achieve the result I wanted, and recreating my favourite OB‑8 string ensemble must have taken more than an hour of careful tweaking because there are differences that must be worked around. For example, the interactions between the sawtooth and pulse/PWM waves are not precisely the same as on the original, and you can't fully open the soft synth's filter using the frequency knob alone, which means that programming an identical filter response can be tricky.

But if I have to voice a single major criticism of the OB‑Xa V it's this: Arturia have retained their horrible "random phase offset" mechanism for trying to emulate the drift of analogue oscillators. This can result in notes that range from warm and deep to thin and weedy, and even occasional notes that speak an octave higher than played due to phase cancellation of the fundamental. This has always been the wrong way to achieve the desired effect, and it's high time that the company came up with a better algorithm. The answer on OB‑Xa V (as elsewhere) is to detune the oscillators by a fraction of a cent so that cancellation is minimised.

There's also the issue of CPU power: OB‑Xa V is ravenous for it. I tested it as a stand-alone application as well as both an AU and VST within Plogue Bidule and Digital Performer 10 and, while it ran faultlessly in all of these environments, it proved to be surprisingly CPU-hungry, especially when used stand-alone. Even with the longest buffers I was able to make it glitch on a 3.1GHz 4-core i7 with 16GB of RAM, so you'll need a powerful host to get the best from it.

Apart from this, any other criticisms are minor. The GUI needs a bit of a debug — for example, the chorus depth is calibrated from zero to 10ms rather than zero to 100 percent — and the on-screen tutorial opens the effects section when it's talking about the modulations section. But far more annoying are the scratches, knocks and fake discoloration that Arturia have used to try to make the GUI appear 'real'. Why would I buy a tatty polysynth when I could have a pristine one?

Conclusions

In many ways, Van Halen's 'Jump' was the worst thing ever to happen to an Oberheim, giving subsequent generations the idea that this is the only sound that you would ever want to wrest from an OB‑series polysynth. But the OB‑Xa and OB‑8 were capable of so much more, generating superb sounds that ranged from lovely warm pads to delicate chimes, from massive basses to powerful leads, and from orchestral instruments to whacky effects. The same is true of OB‑Xa V except that, with its proper oscillator mixer, variable cross-mod, improved LFOs, extended modulation capabilities, stereo spread, increased polyphony, extended unison capabilities, effects, velocity sensitivity, aftertouch sensitivity and automation, it's far more so. As a 16-voice hybrid of the OB‑X, OB‑Xa and OB‑8 it would have made an unparalleled analogue polysynth in 1983 and it makes a damn fine soft synth in 2020.

A Bit Of OB History

The OB‑X was the first of Oberheim's OB‑series. Released in 1979, it was based upon discrete component technology and retained much of the character of the company's earlier SEM-based polysynths. It was larger than the Prophet 5 and felt less robust, it offered limited control over its oscillators, lacked a 24dB/octave filter, lacked filter oscillation and lacked the sophistication of the Prophet's cross-mod but, within its limitations, it could sound superb. This was followed in 1980 by the first version of the largely preset OB‑SX but was replaced in 1981 by the OB‑Xa, the synth that introduced the company's famous blue pinstripe livery. This adopted CEM oscillators and filters and lost the earlier model's oscillator cross-modulation, but it added several new features including a 24dB/octave filter option and the ability to split and layer two sounds across the keyboard. Given such a significant shift in technology, it was remarkable that the OB‑Xa sounded as similar as it did to the OB‑X. The OB‑8 was the final entry in the series. Introduced in 1983, this was an altogether more capable synthesizer and, in 1984, MIDI also became available as standard. It was discontinued in 1985.

Many commentators have written that the best-sounding of the series was the OB‑X, followed by the OB‑Xa and then the OB‑8, but I'm not sure that I agree. The later models sound somewhat different from the first but were much more flexible, so I would pause for a long time before calling any of them either better or worse.

Performance Controllers

The OBs' performance controls were always at odds with conventional practice. It wasn't just that they were paddles rather than wheels or joysticks, it's that they were configured differently. Whereas the standard arrangement has the pitch control to the left of the modulation control, the OBs had them the other way around. What's more, their directions of operation were reversed; you had to pull the pitch paddle toward you to increase the pitch and you had to pull the modulation paddle toward you to increase the amount of modulation. To be fair, new Page 2 parameters in later revisions of the OB‑8 operating system allowed you to reverse the direction of the paddles, but you still couldn't place the pitch-bend to the left where you probably wanted it to be.

Happily, the positions of the two controllers and their directions of operation are conventional on OB‑Xa V, so you can use them without confusion when controlling the soft synth from modern keyboards.

MIDI

OB‑Xa V retains Arturia's usual MIDI mapping capabilities, allowing you to assign a CC to almost every control for performance and automation. To do so, select the MIDI assign mode and almost every knob and switch will turn a fetching shade of purple (unassigned) or red (assigned). Strangely, the hold, stereo and pan switches as well as the vibrato LFO waveforms are not assignable, which seem bizarre omissions. If you click on almost any other control, a window pops open and you can create an assignment by tweaking something on your MIDI controller. You can also determine maximum and minimum values and even invert the response if wanted. Unfortunately, as on previous Arturia soft synths, you can't assign a single controller to multiple parameters.

Once created, can save your MIDI maps so that, if you want to play OB‑Xa V from a different controller, you need only recall a previously saved setup.

Pros

  • It captures the soul of the OB‑Xa and OB‑8.
  • The extensions to the OB architecture are well chosen and hugely increase the synth's capabilities.
  • Velocity and aftertouch sensitivity on an OB‑series synth? Yes please!
  • It offers full MIDI CC control and automation.
  • It's easy to make it sound superb.

Cons

  • It uses Arturia's random oscillator phase offset algorithm, which should have been dumped years ago.
  • Splits and layers can only be accomplished by running multiple plug‑ins.
  • I wish that manufacturers wouldn't 'age' their GUIs. It makes their products look tatty and unloved.
  • It's extremely CPU-hungry.

Summary

Arturia's soft instruments have continued to improve as the years pass, and this is one of its best. It has captured the sound of the OB‑series polysynths and extended their capabilities without undermining their sonic character. That's no small feat.

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Published August 2020