XILS 4 soft synth reviewed

Though overshadowed by later instruments, the VCS3 was used by a number of well-known artists in the early 1970s, including Brian Eno, Pink Floyd, and the Who. XILS 4 is a high-octane software clone of the VCS3.
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A year or two before the Minimoog and ARP 2600 were introduced and started to standardize the voice design of a portable performance synthesizer, EMS was already producing the VCS3. Features that we take for granted today, such as separate envelope generators for the filter and amplitude, were not to be found, but a very forward-looking patching matrix was. Though overshadowed by later instruments, the VCS3 was used by a number of well-known artists in the early 1970s, including Brian Eno, Pink Floyd, and the Who. XILS 4 is a high-octane software clone of the VCS3. Scroll past the video for our full review.


XILS 4 retains the unique sonic character of the original, and also some of the quirks, while adding a host of new features, including polyphony, adjustable levels on all of the matrix patch connections, many more patch connections than on the original, effects, and dual operation with two independent VCS3 synthesizers side by side. It runs as a VST, AU, RTAS, or AAX plug-in. The authorization requires an eLicenser or iLok hardware dongle (not included in the purchase price), but the downloadable demo is dongle-free.

In XILS 4, all signals are handled at audio rate. This gives you more sonic power. It also means XILS will use more of your computer’s CPU cycles. Assuming you have a fast computer, you should be okay.

Depending on how you do the patching, XILS 4 can be either a six-oscillator synth or two three-oscillator synths. One of them can respond to the keyboard while the other responds only to the built-in step sequencer, but they have no key range or MIDI channel settings, so you can’t set up two independent hand-played parts using one instance of the plug-in.

It’s entirely up to you how to configure the signal flow—and that’s both a strength and a stumbling block. There is only one internal “hard” connection: between the envelope of the left or right section and that section’s amplitude VCA. Everything else, including keyboard gate and trigger signals, has to be patched by hand.

Fortunately, the instrument is well supplied with tasty-sounding factory patches, so you won’t need to master the details in order to start making music. But when you start customizing the patches, you can expect to do a bit of head-scratching.

The left and right sections are identical except for one important feature: The left side has a pair of external audio inputs, while the external inputs on the right side receive output signals from the left side.

Each side has three oscillators with wave-shaping, a noise source, a ring modulator, a resonant lowpass filter with three selectable roll-off slopes, an envelope generator, a modeled spring reverb, and non-resonant lowpass/highpass filters for the left and right outputs. The cutoffs of the output filters are one of a very few things that can’t be modulated in real time from within the synth, but not to worry: You can control them via host automation or MIDI CC messages.

In addition to the left and right synth panels, there’s a third global panel containing a variety of modules — an LFO, two extra envelope generators, a voltage processor, a sample-and-hold, three effects (chorus, phaser, and delay), a complex step sequencer, and four audio input sensors (a pitch tracker, an envelope follower, a transient detector, and a gate).

The input sensors allow you to use XILS 4 as a very capable insert effect. It can easily filter or ring-modulate an audio input. You can even patch a signal through its spring reverb emulation and then ring-mod and filter the reverb output.

The secret sauce in XILS 4 is the Analog knob. This adds instability to the oscillators’ frequency, and possibly to the filter cutoff as well. In most of the factory sounds, this knob is set to 50 percent, which is just about right for a slightly unstable vintage tone. The instability is more jittery than the typical oscillator drift heard on other software the tries to emulate analog hardware. With simple patches, the jitter can be a bit obnoxious, but with a more sophisticated patch, you won’t notice it consciously; it will just make the sound more lively.

MIDI control change messages can be mapped to the knobs of your choice using a standard Learn operation. Unfortunately, there seems to be no way to unlearn an assignment, other than by using Learn to make a different assignment. Typing “none” or an unused CC number in the data field in the dialog box doesn’t work. This area of the software needs more work.


Not only does the XILS have a lot more matrix patching possibilities than a hardware VCS 3, it’s possible to patch signals from the left side into the right side. As a result, setting up a patch with separate filter and amplitude ADSR envelopes is easy.

Unlike the VCS3, which accomplished patching with physical pins, XILS gives you a bidirectional mini-knob (it’s shaped like a little red triangle) for each connection. Because the patch panels are small, a handy magnifying-glass button has been provided for zooming in. As you adjust the level of a connection, a pop-up shows its current value, and temporary white lines direct your attention to the input and output whose connection you’re editing. Right-clicking cancels the connection. This is a neat and powerful system, and also overcomes the very significant electronic limitations of the VCS3’s patching mechanism. (The resistors used in the pins didn’t all have the same values, and the pins tended to get lost.)

There are two patch panels for each side, the Main and Extended panels. The Main panel is similar to the patch matrix on the VCS3. It has signal inputs from all three oscillators, the noise source, the ring modulator, the joystick’s X- and Y-axes, and so forth—yes, there’s a mouse-operated joystick. The outputs are intended to receive either audio signals (the audio outs, the VCA, the reverb and filter, and so on) or control signals (for oscillator frequency, filter cutoff, output level, and so on). If this sounds a bit bewildering, it’s because the possibilities are vast.

The Extended panel, intended mainly for control routings rather than for audio, has inputs from oscillator 3 (which is intended as an LFO), the audio input section’s pitch tracker and envelope follower, various MIDI inputs, and so on. The outputs are for oscillator shaping and frequency, filter cutoff, envelope generator decay, and so on. There are also two selectable inputs and four selectable outputs. The selections here include signal sources and destinations in both the left and right synth panels, so it’s a simple matter to do tricks like frequency-modulating a right-side oscillator from one on the left side.

Because the oscillators and filter can be patched directly to the outputs, bypassing the envelope-controlled VCA, creating drone patches that start as soon as they’re loaded is as easy as anything else.


Each side has its own envelope generator. In addition, there are two supplemental EGs in the third panel. Each of the four EGs can operate in either of two modes—the “trapezoid” mode found on the VCS 3, or as a more modern ADSR. Trapezoid mode has attack and decay time knobs, plus a hold time knob (labeled “on”) and an off time knob. If the off time is less than infinite, the envelope will loop. In Trapezoid mode the envelope doesn’t respond to sustained keyboard notes; it just goes until it has passed through the attack, hold, and decay times, and then stops.

When the off time is reduced so that the envelope loops, any of the knobs will also change the total length of the loop, so there’s no practical way to sync a looping envelope to anything. With short loops, helicopter and burglar alarm noises are quite feasible. In normal operation, the looping does stop when you lift your finger from the key, but that behavior can be overridden. If you unhook the connection between Keyboard Gate and Trapezoid (either left or right) XILS becomes a polyphonic rhythmic drone machine.

Effects and Output

XILS 4 has no master output volume. Instead, the output section in each synth panel has separate level and pan knobs for signal paths 1 and 2. These signal paths in the separate panels also have fixed-frequency non-resonant filters, which can be either highpass or lowpass. By using one of each type and panning the two signals to the center, you can create a fixed-frequency notch filter.

The stereo delay effect takes its inputs from these output buses after the pan controls, so you can set up a highpass delay on one side and a lowpass delay on the other side, with separate time and feedback settings. The delay effect is syncable.

The phaser is has a nice tone, and can self-resonate. The chorus is simple, and has a distinctly vintage tone. One of its three modes filters the delayed signal. Another uses only a single delay line, so you can get Farfisa-like vibrato by setting the wet/dry knob to full wet.

Each side has its own “spring reverb.” These modules sound remarkably cheesy—which is what they seem to be going for. Other than the delay time and reverb wet/dry, the effects modules can’t be controlled via the pin matrix.


The sequencer has some powerful features, but it’s not the easiest module to figure out. It can have up to 128 steps. There are three separate sequences, each with two layers, so the sequencer can output up to six independent control signals, plus trigger signals for the envelopes. All three sequences will be the same length, but each can have its own pattern of rests. There’s no way to modulate the clock rate using an internal signal path, but it can be automated in the host DAW.

The upper layer in each sequence has a slew rate control for pitch glides, but the lower layer doesn’t, the assumption being that you’ll probably use the lower layer for velocity data. You can easily use it for pitch if you want to, though. The sequencer can be gated on and off from the keyboard, and it’s up to you whether you want the oscillators’ pitch to track the keyboard while also responding to the sequencer.

The graphic editing of the sequence data is not fancy, but it does the job, at least with shorter sequences; there seems to be no way to zoom in on the data in long sequences, so a rather fussy step editing process will be required. Other features include the ability to run in one-shot mode and MIDI-controllable stop and reset buttons. The patchable outputs for the six layers are oscillator waveshape, oscillator frequency, envelope decay time, reverb level, filter cutoff, and output level. Individual control from the sequencer over parameters like attack time, noise generator amplitude, and filter resonance is not possible.

You can save and load sequencer presets, but in the 1.0 release of XILS 4, trying to do this fails until after you’ve used a menu command to create a random sequence for the first time. I’ve reported the bug.


Some computer company or other once used the slogan, “Think different.” XILS 4 is different. It’s a deep and flexible instrument, and it’s capable of doing sounds, especially vintage electronic tones, that no other synth can duplicate. As I checked out the factory patches, I found myself reminiscing about the old Doctor Who series, whose soundtrack circa 1980 often used sounds like these.

XILS 4 is more difficult to program than most software synths, both because of the need to patch even simple signal routings manually and because a few of the modules behave in odd ways. If you need meat-and-potatoes string pads and electric pianos, XILS 4 may not be your best choice. But if you expect the unexpected, it may well blow your socks off.


Powerful features for synthesis. Great for vintage tones. Works well as an effects processor.


Difficult to learn. No multimode filter. Effects are basic.

Bottom Line

Vintage synth power on steroids.

$199 list | $149 street