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Gmedia ImpOSCar

Virtual Instrument Plug-in: Mac & PC By Gordon Reid
Published May 2004

Gmedia ImpOSCar

Gmedia continue their quest to render the best of the world's keyboards in software form. But will it give OSCar's fans a case of the grouches?

Some people feel that the OSCar is overrated. Its operation seems obtuse, and its lack of a screen or dedicated programming controls makes it feel over-supplied with features. This is barely ameliorated by the fact that most of it is quite straightforward once you get the hang of it, and that nowadays you're unlikely to use its more arcane features. I also rate the OSCar as one of the ugliest synths ever designed, and its construction, while distinctive, is not well thought out. Three aluminium rods turn the two rubber end-cheeks and the guts into a chunky synth sandwich, and if the bolts holding these rods work a little loose, the stresses on the board connections and the panel hardware are almost certain to lead to failures. Then there are the horrible buttons, and pitch-bend and modulation wheels that are partially obscured by the left-hand end cheek... the list goes on and on. If that weren't bad enough, there's the price, which now ranges from £700 to £1400. Given that you could start equipping a home studio for the upper of these, the OSCar seems extraordinarily over-valued.

On the other hand... had Mr Spock been presented with an OSCar (the synth, not the award) he might have raised a single eyebrow and said, "Fascinating". Once you get used to the controls, it becomes very playable, and its combination of digital oscillators, primitive additive synthesis and an unusual filter topology give it a character that makes it stand out from the crowd. Sure, it can create all manner of Moog-y imitations and, perversely, it was for its bass and lead sounds that it eventually became known, but the OSCar is also capable of a huge range of delicate and brittle sounds that you could never obtain from a purely analogue monosynth. Oh yes... and it sounds gorgeous (for more on the OSCar, check out the SOS Retrozone feature at

So, given my dislike of the OSCar's body, but my fondness for its musical soul, I was intrigued when I heard that Gmedia were developing a software synth based upon it. I thought their Mtron imitation of the Mellotron was a brave attempt at recreating the flavour of an almost inimitable original, and I also rated their Oddity plug-in. I therefore hoped they would prove to be the right company to undertake the non-trivial task of recreating this quirky and unusual synthesizer.

Getting Started

Like it or hate it, the original OSCar was certainly distinctive!Like it or hate it, the original OSCar was certainly distinctive!Photo: Mark Ewing

ImpOSCar arrived with a brief but beautifully produced manual and a CD containing four versions of the software: Mac OS 9.x VST, Mac OS X VST, Mac OS X Audio Units, and PC (Windows 98, SE, ME, 2000 and XP) VST. Despite this cornucopia, I was rather disappointed to find no Mac stand-alone version (which, I understand, is planned for a future release at an as-yet unspecified time). I'm a MAS man (ie. a user of MOTU's Digital Performer), and tend not to use VST applications, so a stand-alone version can eliminate many headaches. Anyway, I was unable to use ImpOSCar on my studio's G4 tower because it does not support VSTis, so I loaded the Mac OS 9.x version onto a 1MHz G4 OS X Titanium Powerbook on which I keep a couple of OS9.x VSTi hosts. Everything seemed to be going well until I played a few notes on my MIDI controller keyboard — there was a huge latency, possibly caused by a mismatch between the OS X drivers and the Classic environment hosting my VSTi software. Fortunately, when we contacted Gmedia to resolve the problem, they had the answer ready, in the form of a Gallic VST host entitled Plogue Bidule (French, I am told, for 'Plug-in Thingy'). I downloaded the program from, spent a while getting everything to talk to each other, and... bingo! It worked beautifully (see screenshot on the next page). With an original OSCar to my left, and the Powerbook to the right, it was time to let battle commence.

At first sight, ImpOSCar seems to be an accurate recreation of the OSCar, but all is not what it seems. With the removal of the sequencer, the addition of neater Load and Save buttons, and improvements in the User Wave controls (which we'll discuss later) there is room on the panel for a fourth row of knobs. This has made it possible for Gmedia to extend numerous synthesis functions, and to add a bunch of new ones. So let's look at each of the sections in turn.

The Oscillators

Much of the OSCar's fame is due to its unusual oscillators. These generate five conventional waveforms: triangle wave, ramp wave, square wave, pulse wave, and PWM. Since both the OSCar and ImpOSCar are digital, it's reasonable to assume that these waveforms will be all but identical, and so they initially seemed to be. Starting with Osc1, the triangle waves are almost indistinguishable from one another. Likewise, the ramp and square waves are similar to the original, although the OSCar's are a tiny bit brighter. After a few moments, I began to suspect that this was due to distortion in the OSCar's filter, so I backed the level off by a hair. Yep! That did it.

Hosting a MIDISport 2x2 and ImpOSCar within Plogue Bidule.Hosting a MIDISport 2x2 and ImpOSCar within Plogue Bidule.Significant differences began to appear, however, when comparing the pulse waves. On the OSCar, the PW knob offers a clean sweep from square (50 percent) to a tight pulse. On ImpOSCar, the emulation was near perfect at some settings, while at others there was an unpleasant aliasing, which was particularly noticeable at high frequencies. This was not nice.

The next setting is PWM, which — on both the OSCar and ImpOSCar — offers a single parameter: depth. On the original synth, a dedicated LFO produces the modulation, and turning the PW knob from fully anticlockwise to fully clockwise provides a smooth transition from a static waveform to a rich chorus. This is as true at high frequencies as it is at low ones. However, ImpOSCar displayed an alarming artefact at any pitch higher than about an octave above middle 'C'. This manifested itself as two unrelated frequencies going 'dee-daa dee-daa' at the modulation rate. When SOS made these problems known to Gmedia, they had an updated version back to us within 48 hours, and following the update, everything worked as it should. The pulse wave is now, in my view, indistinguishable from the OSCar's, and I can only tell the difference between the OSCar's and ImpOSCar 's PWM waves because ImpOSCar 's is the cleaner of the two!

In addition to the quasi-analogue waveforms, ImpOSCar offers a further five preset waves derived from the OSCar: Full Organ, Harpsichord, Strong Lead, Double Pulse, and Gritty. But perhaps the greatest trick up the OSCar's electronic sleeves is its primitive additive synthesis...

Additive Synthesis

Creating a user Wave.Creating a user Wave.Without a manual, it is perhaps unlikely that you will stumble across the original OSCar's additive synthesis, since programming it involves an arcane combination of knobs, buttons and the keys themselves. But it can be done, and the results have a brash quality that allows the OSCar to explore sonic territory forever inaccessible to purely analogue synths. So, in addition to the 10 preset waveforms, ImpOSCar offers two further settings — User Wave 1 and User Wave 2 — that allow you to create patches based on either of two waveforms that you program in the grandly named User Wave Matrix. (shown left).

Click on either 'W1' or 'W2' on the Edit Mode knob, and a representation of an LED matrix will appear in place of the pitch-bend and modulation wheels. Within this, you can drag the amplitudes of the first 24 harmonics up and down, doing so in real-time so that you can hear how your changes affect the timbre of the sound. As Paul Wiffen notes elsewhere in this article, this is little different in principle from the method employed on the OSCar itself, but the clarity of the representation, and the ability to see what you've done, makes something that was previously haphazard into something clear, straightforward and useable.

Once you have created a User Wave, you can name it, store it, and recall it as shown in the screenshot on the next page. And, although it may not be immediately apparent, Gmedia have been rather clever here. If you insert a User Wave — say, 'Gordon's Wave' — into two patches, and then edit the harmonic content of one of them, you do not damage the other patch. This is because the patches contain the actual harmonic data; they do not use the name to look up that data within a library. So, instead of wrecking your patches, all that happens when you change the contents of 'Gordon's Wave' in patch 1 is that it becomes 'Unnamed' in patch 2, and the sound remains unaffected. Nice!

OSCar Overdrive

Unlike on ImpOSCar, where they have separate dedicated controls, the OSCar's filter overdrive and main volume were both accessed via the same control, the main volume knob — although they were still independently adjustable. To set the filter drive, you moved the volume control while holding down the Store button. This is at variance with the operation of the control as described by Paul Wiffen in his SOS OSCar retrospective, but following recent discussions with Chris Huggett, Paul has agreed that time had taken its toll on his memory of this when he wrote the SOS retro! This explains, of course, why the Volume control on the OSCar's front panel has the words 'Filter Drive' printed underneath, with an arrow pointing to the Store button (see right).

Filters, Envelopes & More...

Once you have determined your oscillator settings — preset or user-defined waves, octave and so on — you can select Osc2's octave and/or semitone transposition, apply detune, balance Osc1 against Osc2 in the Mix section, and balance the combined sound against a white-noise generator. That's all as it should be and, in the case of Osc2's tuning, much simpler than the method used by the OSCar itself. The signal then passes to the filters (shown below).

ImpOSCar's oscillator section.ImpOSCar's oscillator section.The OSCar offers a pair of analogue two-pole filters that you can configure as two low-pass 12dB-per-octave filters in series, as a 12dB-per-octave band-pass filter, and as two 12dB-per-octave high-pass filters in series. Moreover, the cutoff frequencies of the two devices need not be the same; a Separation control allows you to space them by anything up to a factor of four. This means that you can use the low-pass mode as a traditional 24dB-per-octave low-pass filter, or as dual 12dB-per-octave low-pass filters with two 'knees' in the cutoff profile. Alternatively, you can determine the broadness of the band-pass mode, use the high-pass mode as a traditional 24dB-per-octave high-pass, or as dual 12dB-per-octave high-passes, again with two 'knees' in the cutoff profile.

On the front panel, the OSCar provides six filter modes: low-pass, high-pass and band-pass, each with or without keyboard tracking, which is nominally 100 percent. In addition to all of this, it offers overdrive of the filter input (see the 'OSCar Overdrive' box on the previous page for more on this). ImpOSCar provides all this, but goes further by adding six modes that you could have obtained on the original instrument only by violently molesting the filter circuits with a soldering iron. The nine ImpOSCar modes (of which the first three are equivalent to the OSCar's) are shown in the table below. These modes would have little significance were it not possible to determine the filters' cutoff frequencies independently. However, despite Gmedia's claim that this is unique to the OSCar and ImpOSCar, a similar configuration also appeared on the Crumar Spirit, which was also released in 1983, and which produces a similar range of powerful sounds and 'formant'-style timbres.

Low-pass 24dB-per-octave Dual low-pass filters in series.
Band-pass 24dB-per-octave Dual band-pass filters in series.
High-pass 24dB-per-octave Dual high-pass filters in series.
Low-pass two-pole Dual low-pass filters in parallel.
Band-pass two-pole Dual band-pass filters in parallel.
High-pass two-pole Dual high-pass filters in parallel.
Low-pass/band-pass A low-pass and band-pass filter in parallel.
Low-pass/high-pass A low-pass and high-pass filter in parallel, creating a band-reject filter.
Band-pass/high-pass A high-pass and band-pass filter in parallel.

Instead of offering just 0 percent and 100 percent filter/keyboard tracking, ImpOSCar offers a Keytrack knob that allows you to select values between -200 percent to +200 percent in steps of 10 percent. Likewise, instead of offering a single knob for volume and filter overdrive, ImpOSCar has two: one a conventional loudness control, the other an overdrive control. Turning both to maximum creates the fat sounds for which the OSCar is best known, but you can also use the two knobs on ImpOSCar to create quiet, driven sounds, and loud, clean sounds.

Like the original, ImpOSCar has a dedicated ADSR contour generator for the filter, with an Amount control that determines the depth applied to the cutoff/centre frequencies, and a Delay control that allows you to delay the onset of the filter envelope by up to two seconds after you depress a key. The last of these improves upon the Delay function on the original, which you obtain by turning the Sustain to 'zero', and then determining the length by adjusting the Release.

OSCar front-panel detail, showing the arrow connecting the Volume and Store button. The legend 'Filter Drive' is just visible under the volume control.OSCar front-panel detail, showing the arrow connecting the Volume and Store button. The legend 'Filter Drive' is just visible under the volume control.Just above the filter contour generator, the OSCar and ImpOSCar both offer a dedicated VCA contour generator (shown above). Gmedia claim a fastest response for both ImpOSCar envelopes of 1ms, and a slowest of between 15 seconds and 60 seconds, depending on which knob you're twiddling. However, I wasn't sure that the minimum settings were getting close to 1ms. All other things being set correctly, you can set the filter and/or amplifier envelope Attack and Decay to their furthest anti-clockwise positions, whereupon you should — if the specifications are correct — obtain a precise click lasting just 1/500th of a second. In contrast, the OSCar and ImpOSCar seemed to produce a brief squelch; faster than some 1980s hybrid synths, but not in the millisecond range.

I decided to put this to the test by sampling numerous ImpOSCar clicks and measuring their duration. The results were very interesting and, to give ImpOSCar its due, the VCA envelope's transients ranged from 0.4ms, which is astonishingly fast, to around 3ms, which is still respectably rapid. The tails of the clicks lasted somewhat longer; from almost non-existent to around 30ms at their longest. On the other hand, if I opened the VCA fully by setting its sustain to maximum, I was able to measure the filter response, which was much slower. This time, there was an initial transient lasting around two milliseconds, but this was followed by a tail extending for up to 160ms, and I suspect that this is what I was hearing. I checked this with a range of filter drives and volume settings, just to make sure that I wasn't overloading my A-D converter, or anything else in the signal chain, but the results were consistent.

Loading a user Wave.Loading a user Wave.Like the OSCar, ImpOSCar has numerous triggering and gate modes, and faithfully recreates the OSCar's single- and multi-triggering, external triggering and variable gate time, as well as the envelope repeat modes that work so well with its simple arpeggiator. Of course, Gmedia have extended the principles of the original, in particular expanding the voicing from the OSCar's monophonic and duophonic modes to include four-, eight-, 12-, and 16-voice polyphony. You might think that this would detract from the essential OSCar-iness of ImpOSCar, but I don't think that it does. I prefer to think that it makes ImpOSCar a descendent of the Oxford Synthesizer Company's fabled polyphonic OSCar, the ASG (for more on this, see Paul Wiffen's box later in this article). Given the hushed tones in which people sometimes refer to the ASG, this can be no bad thing.

Finally (in this section) where ImpOSCar now offers the Function knob that controls the polyphony, the OSCar has a knob that activates a 'Hold' function and a basic arpeggiator (see above). ImpOSCar has moved these toward the lower left of the panel, regrettably detaching them from the Triggering and Tempo controls that are explicit to their operation. On a more positive note, the arpeggiator now offers up, down, up/down and random modes, and you can synchronise it to the internal clock or to MIDI.

Modulation & Performance Facilities

The filter section.The filter section.As with everything that has gone before, the LFO (below) expands upon the facilities of the OSCar, upping the original six waveforms to 12. These include 'stepped' waves, a couple of patterns, a unipolar 'guitar' wave for realistic vibrato effects, and a random setting. As on the OSCar, you can direct the LFO to the filter cutoff frequency and oscillator pitch, but — inevitably — the external synchronisation is way beyond what was possible in 1983. There are four options. Firstly, free-run allows the LFO to, umm... run freely. Not an obvious benefit when playing ImpOSCar as a monosynth, the use for this becomes apparent when playing polyphonically, because the LFOs in each of the voices drift in and out of sync with one another. Secondly, Lock does what you would expect; it locks the polyphonic LFOs together. Next, Clock synchronises the LFO to the internal clock driving the arpeggiator, whereas MIDI bypasses the internal clock, and synchronises the modulation to MIDI Clock, if present. If you set the Sync to MIDI, but do not provide a MIDI Clock, you may experience an unpleasant 'hash' as the LFO goes hunting for a synchronising source. I obtained this on the OS 9 version, but not the OS X version, although the problem was my fault for setting everything up incorrectly, not ImpOSCar 's.

In addition to LFO modulation, you can direct the filter envelope (Env2) to the oscillator pitch. You might think this a strange addition to the LFO section, but that's as nothing compared to the 'Env' option in the LFO itself. This allows you to use Env2 in conjunction with the Gate knob to create new LFO waveforms, the rate of which is determined not by the LFO Rate control, but by the Tempo knob (ie. the internal clock) in the envelope section. Weird!

The amplifier, triggering, and polyphony controls.The amplifier, triggering, and polyphony controls.The original OSCar was neither velocity- nor pressure-sensitive, so I am happy that ImpOSCar allows you to control four aspects of the sound using MIDI velocity. These are the rate of the Attack and Release times of both contour generators, the amount of filter overdrive, and the amount of Env2 applied to the filter cutoff/centre frequencies. While not a full complement of velocity-sensitive parameters, these nonetheless facilitate a goodly measure of expression. Unfortunately, aftertouch is conspicuous by its absence. Given that ImpOSCar is superior to the OSCar in so many other ways, it's a shame this wasn't added to Gmedia's version as well.

Conventional 1970s' performance duties are fulfilled using the pitch-bend and modulation wheels, with the oscillator pitches and the filter cutoff frequency as destinations (the relevant controls are shown highlighted on the next page). Strangely, the pitch-bend response is slewed... flick the joystick from the centre to one extreme, and the pitch slides upward or downward over a second or two. Apparently, this was added to avoid audible zippering on the Mac version of ImpOSCar, but it limits the use of pitch-bend somewhat. Understandably, Gmedia are hoping to implement a faster response in a later revision. On a happier note, ImpOSCar 's emulation of the OSCar's six portamento/glissando modes is already spot-on.

The Effects

The arpeggiator.The arpeggiator.In addition to its extensions and improvements in other areas, ImpOSCar offers something completely new: a stereo effects unit. Accessed by clicking on the Panel Open message to the right of the instrument, this reveals 12 knobs and a button that otherwise remain hidden from view (see below). Together with the three 'panel' knobs and the effect On/Off button, these determine the nature of the available chorus and delay.

Of the 16 controls (not including on/off), only three apply to the chorus. These, as you might expect, are Depth, Rate and Level. I rather like this chorus; it adds a subtle dimension to the sound without overpowering it.

The LFO.The LFO.The delay unit is more extensive, with independent Length, Feedback, and Mix controls for the left and right channels, and Delay Level and Tempo knobs available on the main panel. In addition to these, there's a Gate knob, a Delay Units knob that sets the baseline for the Delay Lengths, and a simple Hi/Lo EQ that helps you to seat the delay in the mix. The final control, marked 'CF' is a button that switches between a cross-channel 'ping-pong' delay, and a conventional delay with the left and right channels treated independently.

Of these, the Gate needs extra explanation, because its action is not immediately apparent. When turned anti-clockwise from the 12 o'clock position, it suppresses the delayed signal while a direct signal is present. As explained in the manual, this is an old studio trick that lets the sound cut through without being cluttered by echo while you are playing, but which brings the delays to the fore when you stop, adding ambience at the end of solos and so on. Turned clockwise, the opposite occurs, and at its furthest clockwise extreme, you only obtain delay while you are playing. As the name suggests, this is like gating an echo unit using the direct signal, and it creates some interesting and unusual sounds.


One of the things that made the OSCar special in 1983 was its patch storage. OK, there were only 12 memories, plus 24 factory sounds in ROM, but OSC later upgraded this so that all 36 locations were programmable (don't forget, this was non-trivial stuff in those days!). Perhaps in deference to this, ImpOSCar sound banks comprise 36 patches that you can access using the Load menu provided by your host software or, as I discovered, by dragging the FXB file over the image of ImpOSCar. The manual states that ImpOSCar will also load original OSCar sound banks via SysEx, and I was keen to make some direct comparisons of ostensibly identical patches. However, the utility that makes this possible was not available at the time of writing, so I was unable to do so.

Apart from the lack of aftertouch, ImpOSCar boasts an impressive MIDI specification, and you can control all of its parameters using MIDI CC messages. Many of these are pre-defined, but you can change any of them by turning the Edit Mode knob to 'CC'. Each knob and switch then displays a window containing the letter 'L' (for 'Learn') and the number of the currently assigned CC. If you click on the 'L', the next controller you send will be assigned to that parameter. Six CCs are, however, reserved, as shown in the table below.

64 Sustain Holds all notes.
66 Sostenuto Holds all notes held at the moment CC66 was received.
67 Soft Divide MIDI velocities by a factor of two.
68 Legato Toggle between single- and multi-trigger modes.
69 Hold2 Multiplies release times by a factor of two.
123 All notes off.

Finally, while in Edit Mode, you may also like to change the way in which the mouse turns the knobs. There are two options: Circular and Linear. Unfortunately, the Linear option refuses to work for me, and even prevented me from exiting the mode. I tested this using both the OS 9 and OS X versions of ImpOSCar, and found it to be true in both cases. I suspect that it may be an unwanted side-effect of the unconventional host software I'm using, but it's strange that it happens when running under both VSTi Host and also Plogue Bidule.

The ASG Realised? Paul Wiffen Writes...

As I was paid to help design presets for Gmedia's ImpOSCar, there was no way SOS were going to let me review it. However, my close involvement with the sound design and marketing of the original OSCar (the reason, of course, why Gmedia wanted me involved on ImpOSCar) also meant that I was well placed to write some additional historical background to supplement Gordon Reid's review, as well as some subjective comments about ImpOSCar. Those who worry about such things should therefore be aware that everything I say here about ImpOSCar is against a backdrop of having been commercially involved with the design of the presets for the instrument — make of that what you will.

The full story of my involvement with the original OSC project can be found in my September 1999 SOS Retrozone article (a web link to which can be found near the start of this review). I programmed 32 sounds for the OSCar back in 1982 on a work-in-progress development unit with no front panel and paper labels for each knob at designer Chris Huggett's house, and loading these same sounds into ImpOSCar last year was quite a spooky experience — it was as if a missing section of my life had suddenly been returned to me. Within minutes of encountering ImpOSCar, I was re-living the experience of programming one in a way I hadn't been able to do for nearly 20 years. In the OSC days, my demo OSCar was always being taken away to fulfil an order somewhere (I particularly remember serial number 1000 going to Vangelis when I had hoped to hold onto it) and although it always got replaced, it meant there was never one to call my own. More recently, I was given one by a kind soul for my 40th birthday, but unfortunately, I left it in the studio of another friend who has now emigrated to South Africa (if you're reading this, Jethro, please get in touch!).

As Gordon says elsewhere in this article, ImpOSCar offers much more than the OSCar ever did, and the two big improvements in this regard really struck me when I demonstrated ImpOSCar for Gmedia at this year's NAMM show in January. When you're programming sounds, you don't notice polyphony so much, as you tend to be striking a single note over and over, and until you come to play for real in front of people, you don't realise how important velocity sensitivity is to performance.

Those with very long memories might remember that there was to have been a velocity-sensitive polyphonic product from OSC, which was announced and even demonstrated by yours truly at the 1985 Frankfurt Musikmesse. Called the ASG (Advanced Sound Generator), it was housed in a rack to avoid the problems of having to develop a velocity-sensitive keyboard (that then-recent innovation, MIDI, meant that any other keyboard could be used to trigger it with velocity), and featured a large LCD display so that the additive waveform facility could be more easily programmed. As one of the few people ever to play the ASG, I can attest to the fact that velocity sensitivity and polyphony made a big difference to the sound of the OSCar and unsurprisingly, the same is the case with ImpOSCar. It reminded me of the first time I played the ASG just before we took it to its German launch — I thought at the time how much it changed the character of the OSCar to be able to trigger it polyphonically, with each voice changing subtly depending on how the velocity was routed to amplitude and filter. I always thought that the ASG had a very Oberheim-like quality which I never noticed on the monophonic OSCar (although the voice cards at the heart of both synths were exactly the same) and the same is true of ImpOSCar.

Used this way, ImpOSCar is in fact the equivalent of 16 OSCars (£11,184 at 1984 prices) or a fully loaded ASG (which would have been better value at its £2999 target price, had it ever been released). I suppose we should no longer be surprised that a virtual synth can outperform its original real-world inspiration, because all the physical requirements for each voice of polyphony in a hardware synth are sidestepped. Once the voice architecture has been recreated in the digital domain, then creating multiple voices is simply a question of assigning CPU power sufficient for as many voices as you want to trigger.

This is a far cry from what happened with OSC's ASG, which housed up to 16 OSCar voice cards. I seem to remember that the plan was to offer it in an eight-voice version for around £1999 and a 16-voice version for £2999. However, to my knowledge, that 1985 Frankfurt show was the only time the prototype held a full complement of OSCar cards. The problem was that once we got back from the show to business as normal, we never had enough voice cards and Chris Huggett would have to keep 'borrowing' them out of the ASG to make up an order. By the time OSC ceased trading as a manufacturer, all the voice cards had been used to sell the last few OSCars, and the last time I saw the ASG prototype, it was mute, as all its voice cards had been cannibalised. At last, I feel that the concept has been fully realised.

I particularly enjoy creating additive waveforms with ImpOSCar. Although the way that you built up waveforms on the OSCar was fun (repeated hitting keys on the keyboard to increase the proportion of the corresponding harmonic in the resulting waveform) and could be used live to subtly change the harmonic content of the waveform (I seem to remember one of the tracks on Jean-Michel Jarre's Rendezvous opening with this effect), it was very difficult to keep track of how many harmonics were present, and what the relative strength of each one was. With the graphical harmonic display of the ImpOSCar, you can see at a glance which harmonics you are using, and what their relative levels are, and altering this balance is simplicity itself with the mouse. It's also great to have the Delay and Chorus built in and tempo-sync'able.

All in all, ImpOSCar really delivers on the potential of the OSCar in a way that Chris Huggett and I were never able to do in the OSC days because of lack of capital (we had several meetings with Ultravox's management about investing in OSC to enable us to get the ASG to market, but they decided to buy their parents all houses instead). Now if we can just get Gmedia to make ImpOSCar load and process samples, as Chris always planned to do with the ASG, then it really will be the instrument that I always dreamt of. Paul Wiffen

Many thanks to Tim Goodyer, former editor of Studio Sound, and now the Editor of Pro Audio Asia, for the loan of his much-loved and beautifully preserved OSCar throughout this review.

In Use

On the simplest level, using ImpOSCar couldn't be easier. Select a preset from the drop-down list in the 'Selected Patch' window, and play. If you want another sound, select another patch, and away you go. Likewise, editing is straightforward and intuitive, albeit with one frustrating twist. I didn't discover until the end of the review that I could use the Apple key and click on a knob to set it to a sensible default, such as 0 percent, 50 percent or 100 percent (as appropriate). It would be nice if this was mentioned in the manual.

Performance features.Performance features.Furthermore, despite the clarity of the control panel, it initially seemed that some of the knobs are rather coarsely quantised, although they are not. To obtain fine adjustment, you have to click on a knob and then move the cursor a fair distance away from it to obtain smaller angular changes. Using this method, values that jump by, say, 0.15 at a knob's rim change by as little as 0.01, as they should.

Having twiddled a few knobs, it took me a while to realise that there is no need to 'Save' changes because edits are retained in the current patch (you can return to the unedited patch at the click of a button, so all is well). However, this leads to another minor annoyance... you can only edit a patch and save the results elsewhere through a long-winded method of storing it in a temporary buffer, resetting the current patch to avoid losing it, choosing a new patch, and then recalling the edited version, entering it into the new location from the buffer. What's more, saving complete banks of sounds is achieved using the host application, but for me there was no 'single patch' load, and therefore no way to combine patches from disparate files into a single bank of presets. Apparently, many users will obtain this facility via their host software, but others will not be so lucky.

Nonetheless, I'm more than happy with the sounds produced by ImpOSCar, and I was soon using the conventional waveforms to develop patches ranging from the expected (and still superb) bass and lead sounds, to rich imitations of solo strings, solo brass and traditional bleepy and squelchy synth sounds. I then sent myself wandering within the OSCar's digital realm, finding it easy to create patches that stepped way beyond the norm. These were bright, often percussive, and sometimes harsh sounds including bells, chimes, and all manner of strange effects. If ever a synthesizer had two distinct characters, it was this one.

The Effects window.The Effects window.Of course, what many people will want to know is whether it sounds like the real thing. The short answer is, "it can be astonishingly similar, particularly in the bass registers... in fact, it's sometimes all-but indistinguishable from the OSCar". But I'm too old and ugly to leave things at that, so now I'm going to be a bit more clinical and point out that there are small differences when comparing each of the OSCar's sections against those of ImpOSCar. This is not just a question of the envelope responses and shapes being slightly different (though they are) or of the filter and resonance characteristics being slightly different (though they are) or even of the overdrive and volume characteristics being slightly different (though they are, too). It's simply that, if you create a patch on the real thing, and then try to recreate it on ImpOSCar, it's not always the same. Try setting up a basic sound on both: one oscillator, fully open low-pass filter, organ envelopes, and no modulation. You'll be hard pressed to differentiate one from the other. But do something as simple as close the filter and use the filter envelope to open it, and you may hear a difference. On a superficial level, you can attribute some of this to differences in the visual calibration of the controls. For example, if you set all the knobs that control the filter envelope to 12 o'clock, you'll obtain a much faster sweep on ImpOSCar than on the OSCar, with a higher cutoff frequency in the sustain segment. But even with experimentation, you may not be able to program the sounds to be identical. Are these differences significant? I don't think so, but you might disagree.

So let's move on to the aspects of ImpOSCar that cannot be compared to the OSCar, simply because they do not exist on the original synth. Primarily, this means the Effects section and the polyphony. Set ImpOSCar to four-, eight-, 12-, or 16-note polyphony, and you'll find that it's a master of rich strings, punchy brass sections, and evolving pads that shriek 'Prophet' or 'Oberheim' at you. I was impressed by the depth of the sound, especially once the pulse and PWM waves were fully available to me. I was also amazed at how organic it could sound, and even used it to create an imitation of one of my favourite Polymoog organ sounds (Genesis, circa 1978). Adding a touch of chorus and delay, I was even creating lush imitations of 1970s string synths. In short, the combination of the OSCar's quasi-analogue voicing with 16-voice polyphony and effects is gorgeous.

ImpOSCar with the effects and user waves visible.ImpOSCar with the effects and user waves visible.The polyphony and effects also bring many digital patches to life, and I can imagine fans of the PPG or even some DX owners being happy to experiment with ImpOSCar to obtain percussive sounds as well as ethereal, digital pads. Finally, I found that invoking one or more parameters of velocity sensitivity adds yet another dimension, and although one shouldn't be too keen to sling lashings of effects, polyphony, and velocity response at every patch, this is good stuff.

If I have a reservation, it's this: ImpOSCar perhaps tries too hard to be an OSCar. Think of it as an excellent polyphonic softsynth inspired by the OSCar, and I'm certain that you won't be disappointed.


For a long time, I was not a fan of software synths, finding them less intuitive and less musical than their hardware brethren. However, my view is changing, and much of the credit — or blame — lies at Gmedia's door. I like Mtron, and the Oddity was the first software synth I used that combined an accurate representation of its inspiration, a good user interface and watertight operation. With ImpOSCar, the company has gone still further and, now that everything works correctly, the additional benefits outweigh any reservations I might have had.

So, would I buy ImpOSCar? On the one hand, there's a certain kudos in owning a real OSCar, although I couldn't recommend that anyone purchase one at current prices. On the other hand, ImpOSCar is very affordable and, while you lose immediacy, it's going to be more reliable, it's more flexible, and you gain hugely in areas such as additional LFO waveforms, extra filter modes, improved overdrive/volume controls, keyboard tracking, and velocity sensitivity... to say nothing of MIDI control, 16-voice polyphony, and effects. The final point to make is that I've used OSCars off and on for two decades, and yet if I hadn't had one here for direct comparison, I wouldn't have been able to say for sure that the sound of ImpOSCar was any different from that of its inspiration. 'Nuff said, I think.


  • Not just an OSCar... it fulfils much of the promise of OSC's unreleased ASG polysynth.
  • It offers additional features in all areas of synthesis, such as velocity sensitivity, the simple but useful effects section, and the 16-voice polyphony.
  • It generates a huge range of analogue, digital, and hybrid sounds.
  • I've been hammering it for over a month, and it hasn't crashed yet!


  • There's no stand-alone version available yet.
  • There's no aftertouch.
  • The pitch-bend response is slewed too slowly.
  • Saving to a new location and compiling banks of patches from an existing library is rather convoluted.


ImpOSCar is an excellent attempt to recreate the sound and feel of the original OSCar. However, its hugely enhanced facilities make head-to-head comparisons with the original synth a little pointless, so I prefer to view it as a powerful, polyphonic softsynth rather than as a slavish imitation of the OSCar. Highly recommended.


£99.95 including VAT.

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