Patchable Analogue Monosynth

This quirky rack synth not only offers that genuine analogue sound, but comes with built in MIDI interfacing and a very useful degree of patchability, for exciting sound-design potential.

Spawn is the latest synth to emerge from Cornish company Analogue Systems, best known for analogue modular synths. If you're a real analogue fan, your dream setup is probably such a system, covering a studio wall and festooned with patch cords. And if you've several grand spare, you can have it, brand new. But what if you lack that kind of money (or space), but still crave access to some of the interesting routing possibilities and sound-creation potential of patchable synthesizers? Spawn could well offer a compromise.
Like Korg's 1970s MS20, this rackmount analogue monosynth starts with a fixed signal path, via which it's easy to create a variety of powerful sounds by knob tweaking. However, an array of front-panel sockets also means that rather more complex sound design, plus integration with other analogue instruments, is just a few patch cords away...

Features Overview
Spawn's fixed signal path follows the traditional voltage-controlled oscillator (VCO), voltage-controlled filter (VCF), and voltage-controlled amplifier (VCA) model, with modulation provided by a voltage-controlled LFO (low-frequency oscillator) and an Attack/Decay/Sustain/ Release (ADSR) envelope generator. This architecture reminded us immediately of Roland's SH101 and like that classic monosynth, Spawn even has a square-wave dual sub-oscillator to help beef up the bottom end. Differences become apparent on closer examination, however. For example, the VCO has a fully variable waveform generator, providing a wider variety of sounds than fixed waveforms can. Spawn also differs courtesy of its comprehensive built-in MIDI-to-CV converter which also works with external analogue equipment.
But the main difference between Spawn and most single-oscillator vintage monosynths is that its internal signal path can be subverted by simply repatching. This offers much more in the way of sound-design options than the uncomplicated design might suggest, as well as allowing you to link patch cords between Spawn and many other analogue instruments, for CV/Gate control and audio signal processing. No fewer than 37 3.5mm gate, CV and signal mini-jack ins and outs are provided; Analogue Systems even supply 10 patch cords to get you started. Because Spawn has both CV/Gate connectivity and MIDI controllability, it can be played via an analogue synth keyboard or analogue sequencer, as well as from a MIDI keyboard.

First in the signal path, if not on the front panel, is the VCO, equipped with a waveform knob morphing from a sawtooth, through a square, to various widths of pulse wave, ending on a five-percent pulse wave. As you'll know if you read last month's Synth Secrets, the 'up' and 'down' parts of a pulse wave aren't equal, creating different textures; a five-percent pulse is somewhat nasal in character, rather than the clarinet-like or reedy tone you get from a symmetrical square wave. Morphing is continuously variable through a range of hybrid waveshapes, but you may notice that there is no specific triangle wave.
A sine wave is also conspicuous by its absence, but don't worry: the filter produces one when coaxed into self-oscillation with high resonance. Additionally, closing the filter rounds the edges of the VCO's waveform, particularly when the knob is between sawtooth and square waves; this produces something close to a sine wave. In any case, sounds typical of triangle and sine waves can be achieved with careful programming.
If one oscillator seems stingy, that dual sub-oscillator (found in the Source Mixer section) can be added in variable amounts to beef up your sounds. Turning its knob left adds a square wave one octave below main VCO pitch, while turning it right makes the square wave track oscillator pitch two octaves lower. This sounds very effective, and a simple patch makes it even better: by taking a lead from the '-2' sub-oscillator output to the Source Mixer's 'Sig In' signal input, you can mix both -1 and -2 square-waves with the main oscillator, adding remarkable depth and weight.
The tuning of the VCO is slightly unusual, though not incomprehensible. First, there are three tuning modes, '0', '-2' and 'W, selectable via three-way switch. With the Tune knob set to the central, '0', position, the VCO generates a pitch of 64Hz. Turning the knob full left lowers the pitch by an octave, and turning it fully right raises it an octave, providing a tuning range of 32Hz-l28Hz. The '-2' position drops central pitch to 16Hz, again with 1 octave Tune knob range. Play really low notes with the Octave setting at -2, and individual waveform cycle clicks are audible. This shifted setting becomes more generally useful when Spawn is played via analogue connections, helping to make allowances for analogue controllers with a limited voltage range. If your controller doesn't have a wide enough range, you may be unable to play Spawn in its proper 'bass' register (it has no octave settings as such), so shifting it down two octaves brings the VCO into an appropriate range.
The mathematically astute will have noticed that 64Hz doesn't relate to any equally-tempered pitch: the 'C below middle 'C, for example, has a pitch of around 65.4065Hz. This means that Spawn needs to be tuned up from its central pitch to match your other instruments. Fortunately this is very simple. However, a little of that useful 1 octave tuning range mentioned above won't be available, because you have to move the tuning knob slightly right to get the synth up to pitch. As a result, it will be about 50 cents short at the full +1 octave travel of the Tune knob. In the opposite direction, full travel will be 50 cents flat, so you'll need to fine-tune to bring it up to pitch.
The final tuning mode is 'W, for Wide. In this mode, the Tune knob controls a 12-octave (1Hz-12kHz) frequency range, centred on approximately 64Hz (in practice, there's a slight, but easily tuned, discrepancy between the centre frequency of Wide and '0' modes). The Wide option gives an unusually broad tuning range, though it's fiddly to set different central pitches in this mode. It's probably applicable in a sound design context, where Spawn's VCO would be more of a modulation source for another synth using a wider frequency range allows a greater variety of modulation effects to be created.
Incidentally, low-noise op amps have been used in the synth's circuitry, and care has been taken to ensure good temperature sensing and operation. As a result, we can verify that there is no (or very little) pitch drift when using Spawn even for long periods of time.
The VCO can be played from an external analogue source via a CV input. A Glide knob controls the amount of portamento applied to the VCO. This knob doesn't work when Spawn is being played from its MIDI interface: as discussed later, glide is then initiated via MIDI Controllers.

VCO Modulation Options
Spawn's oscillator can be modulated in a number of ways. There are two fixed modulation routings: oscillator pitch modulation and waveform modulation. The former is applied via a 'Mod' knob by the Tune knob: turn it left and increasing amounts of LFO triangle waveform are applied (for vibrato-like effects); turn it right to add square wave for tremolo or trill effects. The waveform modulation knob again labelled 'Mod', but adjacent to the Waveform knob is also dual-state. In this case, turning it left adds LFO triangle wave, but turning it right applies the EC curve to the VCO waveform. Essentially, modulation added in the latter way morphs through the waveform options, as if you were moving the Wave knob manually, creating a rich pulse-width modulation effect, even with waveforms that are more sawtooth than square.
Both pitch mod and waveform mod are controllable via CVs, courtesy of dedicated input jacks and associated bi-polar Depth knobs. Thus, a CV can be routed from Spawn, or an external instrument, for added variety and sophistication in the modulation department.
With only one oscillator, you can't create oscillator sync within Spawn. This effect which causes the cycle of one oscillator to sync to that of another, producing a harmonically rich sound perfect for powerful and hard-edged solos can be achieved using an oscillator from another analogue synth, in conjunction with Spawn's oscillator. The other oscillator must be patched into the Sync input on Spawn, provided for just this purpose, then played from Spawn's MIDI-to-CV converter.

A Little Background...
Spawn was designed by Andy Pledger, with Input from Steve Gay, Analogue Systems' lead designer. Andy is an alumnus of the London College of Furniture electronic music courses run by Tim Orr of EMS, and is an extension of a similar instrument made in limited quantities under the SMS (Synthetic Music Systems) brand, as the MARS (no relation to the Vermona instrument of the same name). Some circuit ideas (and a variant of the RS140 MIDi-CV converter) were inherited from Analogue Systems' RS Integrator family, so Spawn adds a different but related sonic character to an existing AS setup. Currently in development is the Pod expander, which may combine a mix of circuitry from Andy and the AS range. It's too early to be definitive, but expect an extra VCO, multi-mode VCF, ring modulator and other goodies, again with a preset signal path, but patchable to itself and Spawn, creating a flexible two-VCO/ two-VCF/two-EG synth with MIDI control.

Source Mixer
The Source Mixer is a simple device for balancing relative levels of the parts of a sound main oscillator, sub-oscillators, noise generator, and (theoretically) an external audio signal. First up, the Signal knob controls VCO output level to the filter; this output can be overdriven, subtly 'saturating' the sound. The sub-oscillator control mentioned earlier also lives in this section, as does a white-noise generator. As well as being added to a sound via the labelled knob, noise can be routed elsewhere via its own output. Lastly, there's the Sig In jack mentioned above, which can give external audio access to the filter. However, because this input is set at a level of 10V, to match the sub-oscillator '-2' output, external line-level audio never seems loud enough for proper treatment, which is a shame. We tried to preamplify some signal, but the level still wasn't high enough.

The Filter
If there's any single thing about an analogue synth that determines character, it's the filter. That specified for Spawn is a 24dB-per-octave resonant low-pass ladder filter (as seen on old Moog synths), made of 10 matched transistors. The result is an indefinably classic sound: pure and fat, accurate yet warm. One gets the feel of an ARP filter (early 2600s featured a ladder filter), but with some of the fuzz of a Moog.
Spawn's VCF has a 20Hz-20kHz frequency range and features a Resonance control that can be tweaked to self-oscillation, producing a pure sine wave, as mentioned above. The sine's central pitch is determined by the Frequency control, so it can be tuned for melodic playing; it's not ideal or completely stable, but it's worth having.
Of course, the filter can be modulated by both the LFO and Envelope Generator, but since there is just one of each on board, any modulation or EG contour applied to the filter will be the same as those applied to other elements in the signal path, such as the VCA and VCO. The Modulation knob applies a triangle or square wave from the LFO to filter frequency, while the Envelope knob applies a positive or (usefully) a negative envelope shape. Thus classic or inverted filter sweeps can be created.
In addition to these fixed routings, the filter can be modulated via two CV inputs, one with a positive/negative modulation amount pot. Typically, either of these inputs could route velocity from Spawn's MIDI interface to filter frequency, for a useful velocity response to playing attack (Spawn is not velocity sensitive unless you patch it to be), or to route other LFO waveforms to filter frequency. There's also a preset way of remotely altering filter frequency via MIDI, as Spawn has MIDI Controller 11 (Expression) assigned to this parameter, allowing real-time performance modulation without patching. A preset link between the MIDI interface's CV output and filter frequency offers basic filter keyboard-tracking (the filter opens on a 1 V-per-octave basis). However, routing a MIDI interface CV to the VCF's CV2 input, which has the positive/negative amount knob, allows customisation of filter tracking, to open up the filter as you play higher (or lower, if preferred) on the keyboard.

Spawn's waveforms as traced by the Scopion plug-in in Steinberg's Cubase VST. First is the basic sawtooth, followed by something mid-way between a saw and a square (top), then the square and a pulse wave with a duty cycle of five percent. The last one (left) shows the wave produced by filtering a sawtooth, which is pretty sine-like.

VCAs are seldom interesting parts of a synth's signal path. However, Spawn's VCAs its main VCA is augmented by a second, MIDI-controlled VCA, of which more in a moment are distinct elements that can be exploited creatively in their own right. Main VCA controls are few: firstly, the Signal pot, with overdrive, is effectively Spawn's overall output level control if nothing special is being done with the synth's signal path. The only other control, the Envelope knob, governs envelope amount, and also sets linear or logarithmic response to the EG (linear being the normal choice for a standard EG shape). There are CV inputs for the VCA, so an external device's EG, or a modulation source elsewhere in Spawn, could be routed to modulate volume.
Further flexibility comes in the shape of a VCA In, useable for routing audio that has been sent out via the VCF output, and treated externally, back into the synth. An example might be sending a post-filter Spawn signal to a distortion unit, then feeding it back in to be finished via Spawn's VCA and EG. The VCA input also accommodates an external audio signal happily, it doesn't suffer from the filter's 'Sig In' external audio level problem which can be contoured with the EG, if desired.
The second, MIDI-controlled, VCA (called the MIDI-CV Mod VCA) is rather confusingly arranged and labelled its four signal and control sockets are in the middle of the VCO section. Also, the early version of the manual we had didn't really explore the implications of this nifty extra, describing it as a 'performance-oriented VCA'.
Without repatching, mod wheel data (usually from your MIDI keyboard) appearing at the MIDI interface is routed to control the MIDI-CV Mod VCA. This does nothing, however, since no audio or control signals are
pre-patched to the VCA. In order to use this VCA, you have to patch something to its one input and two outputs. Sadly, we found that the preset routing of the mod wheel doesn't work well even when you do make an appropriate signal or control patching: a full
mod-wheel move on our keyboard had minimal effect. Luckily, the MIDI VCA also features a CV In, and patching the Spawn MIDI interface's mod wheel CV output to the MIDI VCA's CV input created the desired effect. Our favourite use of the MIDI VCA is to route the Velocity output of the MIDI interface to the MIDI VCA's CV input, and route the VCF output through the MIDI VCA to the main VCA Input. The result is instant velocity-sensitive level changes. Placing LFO amount under velocity control is also useful (route LFO output to MIDI VCA 'Signal' input and a MIDI VCA's Out to the LFO's destination). The result is increased modulation depth in response to higher playing velocities.

The MIDI Interface
Some current analogue synths lack a MIDI interface. There's something to be said for the pure analogue approach, but it does force the newcomer to buy a MIDI-CV interface In order to Integrate the synth into a contemporary studio. Analogue Systems' approach is perhaps the best, especially since Spawn's MIDI interface is so nicely implemented.
With no additional patching, the MIDI interface allows your MIDI keyboard to play notes on Spawn (with 1 octave of pitch-bend), change VCF cutoff frequency (via MIDI Controller 11, Expression), control MIDI VCA amount (with the mod wheel), and both activate glide and set glide time. A CV is also routed to the VCF, providing preset keyboard tracking of filter frequency. Curiously, there is no sustain pedal response.
The interface's 10 output sockets can be used within Spawn to create more interesting MIDI-analogue modulation routing, or let you control one or two analogue synths or modular VCOs from your MIDI keyboard (even when also playing Spawn itself though obviously, all connected synths will then play the same notes). The MIDI interface can be isolated entirely, too Spawn sits between MIDI keyboard and the other analogue synth, lending its interfacing capabilities. Both Gate and Trigger outs are provided, for triggering (and retriggering, in the second Instance) EGs on external synths. In addition to these basic connections, various MIDI controllers are converted to a handful of CV outputs: velocity, aftertouch, mod wheel, breath controller and expression (the last two being bi-polar). An S-Trigger, producing a negative trigger for use with certain Moog and Korg gear, is also provided. However, the Hz-per-Volt CV option required by some Yamaha and Korg instruments is not implemented.
Finally, two types of triggering response are provided: Single and Multiple. With Single triggering, when you press a key, any key you
press afterwards causes a change in pitch but won't re-trigger the EG. You need to actually release a key before playing a new one, to initiate the EG. This mode is ideal for legato playing. The envelope is retriggered with every new note in Multiple Trigger mode, although over MIDI, only lower notes than the first played retrigger the EG. Surprising results can be produced if Spawn Is played via direct MIDI connections alongside manual patching from the MIDI interface. For example, making a CV connection to the VCO CV input and playing Spawn via MIDI produces a two-octave pitch range between each octave you play: in other words, every semitone plays a whole tone. This Is probably a side-effect of cumulative voltages and not an effect everyone will want, but it might come in handy sometime! If you isolate the MIDI interface and track oscillator pitch via the VCO's Pitch CV input from an interface CV out, it's even possible to set up quarter-tone tuning, with care.

The Envelope Generator
Essentially a modulation source, the EG produces a voltage that changes over time and which in Spawn's case can be routed to amplitude or VCF cutoff frequency. In the first instance, a change in volume is produced and in the second a change in timbre. As you'd expect, Spawn's EG has four stages, with Attack, Decay, Sustain and Release portions. Attack ranges from a fairly snappy five milliseconds to 7.5 seconds, and Decay and Release both have a range of five milliseconds to 1 5 seconds. That's not quite as long a release as we'd like for all purposes, but it's still a sensible value.
Spawn's EG has a number of sockets: the Env Out lets you route the EC's CV to any suitable destination on this or another synth, while the Gate and Trigger input sockets determine how the EG behaves when triggered via analogue connections. This seeming redundancy makes sense when you know that some analogue controller keyboards are equipped with Gate and Trigger outs; the Gate is the normal mode for initiating the envelope, and the Trigger tends to be a short pulse to retrigger the envelope while, typically, a legato passage is played.

"Musicians aufait with analogue synths will be kept interested for ages."

Also, modulators or rhythmic trigger pulses could be routed to this input for gated synth effects while you're playing a melody from your controller.
Unusually, the EG has a 'Mode' selector. Most users will leave the switch at its central, 'ADSR', position, which makes the EG behave as normal. The position labelled 'Gated Repeat' causes the Attack and Decay portions of the envelope to cycle repeatedly while you hold down a key on your controller keyboard. The rest of the EG curve plays out when you release the key. This turns the EG into another, LFO-like, modulation source. Modulation speed is set by the Attack and Decay knobs; turning both fully left creates the fastest cycle, a ring mod-like blur. Moving the Decay knob right slows the cycle down, creating an instant one-finger repeating note effect, suitable for a simple bass line and changing Attack has an effect both on speed and the output CV's shape.
The last EG Mode option is Auto Repeat, which causes the EG to cycle its Attack and Decay portions indefinitely without requiring you to play a note useful, perhaps, for sound design, or for when using Spawn as a sound or control source in a larger setup.

The last link in the synthesis chain is also the first on the front panel: the voltage-controlled
low-frequency oscillator. When they say low frequency, they mean it: it has a range of 0.055Hz (one cycle every 18 seconds) to 33Hz. An LFO is used as a modulation source, and if you've read this review in a linear fashion, you'll know that the main things that like to be modulated include oscillator pitch and filter frequency, though the LFO can produce interesting effects when routed to less expected destinations. It produces positive and negative sawtooth, square and triangle waveforms. One would normally expect a sine wave, too, but the triangle gets reasonably close, and certainly produces the vibrato-like effects normally expected of a sine used as a modulating LFO. We did miss not having a sample-and-hold/random waveform, which would be especially good routed to filter cutoff frequency.
Having all the LFO waveforms available on individual jack sockets helps compensate for having only one LFO: the different waveforms, when patched into CV inputs, produce different textural effects that can complement the preset triangle and/or square wave available on VCO and VCF Mod knobs. The speed will always be identical, but the LFO effect can differ for up to four destinations.
The Voltage-controlled' part of the LFO's name (it's even written VCLFO on the front panel) is not incorrect: alongside the waveform CV outputs, there's a CV input providing hands-off control over LFO rate, so it can be changed dynamically during a performance or cross-modulated from another source for sound design. One useful patch is Velocity from the MIDI interface to the LFO CV input, which changes LFO rate according to velocity. If you used aY-lead to trigger VCF Frequency simultaneously, a nicely expressive performance could be created.

Quiet At The Back
Given that this is a patchable synth with most of its Important connections on the front panel for obvious reasons, the rear panel is, unsurprisingly, somewhat less interesting. The quarter-inch Jack audio output is a duplicate of the front-panel VCA Out; you don't need to use it unless to leave it connected to an audio patchbay or mixer. The 115/230V power supply is built in, and the power switch is located at the rear, making life more difficult if Spawn is racked. Spawn's MIDI input channel is also selected, inconveniently, with a rear-mounted switch. The MIDI In itself Is on the back panel, along with a MIDI Thru. There's also a DC calibration socket for engineers and emergencies only!
The synth is sturdily built into a 2U aluminium rackmount, with solid pots and switches. It's not especially cosmetically sophisticated, but bright blue LEDs add visual cachet, and the front panel is clean and readable. Knobs are well-spaced and accessible, although this becomes less the case when more than a couple of patch cords have been spread around! Korg's solution with their MS20 restricting jack sockets to one section of the front panel, away from the knobs wouldn't be practical on a compact rack synth like this.


What Writing Is For
For newcomers, it's worth mentioning that an analogue synth of this nature has no patch memories. The manual includes a photocopyable sheet for recording settings the old-fashioned way that is, with a pen and luckily, the synth is stable enough that you stand an excellent chance of replicating sounds later. One safety feature that's easy in this digital world is printing a Spawn performance to a track of an audio sequencer, so you can refer to it if you need to replicate a track in future.

It's hard not to like Spawn; it's a fine blend of classic design, great sound, stable electronics, ease of use, and future-proofing courtesy of its semi-modular design. It sits well in the current market of modern analogue synths, and should be especially attractive for newcomers to the field who would prefer to take the hardware, rather than software, path to creative synthesis, but are daunted by the thought of assembling a truly modular system. That said, musicians au ffl/twith analogue synths and synthesis will be kept interested (and busy) for ages by this one, as its patchable nature invited experimentation. We obtained a very wide range of sounds with it, from gutsy, sub-y and resonant basses, through ethereal, mournful, impressionistic lead/melody timbres, to classic spiky, tinkly sounds perfect for analogue arpeggios controlled from our Korg Mono/Poly's arpeggiator. Not to mention the strange, abstract and atmospheric tones that come in handy for background textures, song intros and so on. We've also been enjoying multisampling its unmistakably analogue timbres for polyphonic use in sample-playback software.
Weaknesses are relatively minor in context. One would always like, ideally, at least a second full oscillator, though the sub-oscillator makes up for this to an extent. Likewise, separate ECs for filter and VCA would be better than a shared one. Such extras would make the instrument more costly, however. It's a shame that the audio input to the filter isn't more useable, and the layout and labelling of the front-panel controls and sockets was a bit of a barrier until we'd become familiar with the manual.
But such shortcomings are more than countered by how useful this synth is. It's versatile enough to use with both analogue and MIDI gear, and can expand the sonic potential of other analogue synths you have. It offers ease and speed of programming if you want it, but also plenty of complexity if you venture into patching (on that subject, the inputs are even nicely buffered, so pretty much anything can be plugged anywhere without frying the circuitry!). It's also brand new, which puts it ahead of vintage analogues in the reliability stakes. Finally, it's very space-efficient for the modern studio. This synth would be a very good addition to an all-software setup, as it provides genuine analogue depth and warmth without the fuss. Because, actually, as good as software synths are these days, when they're side-by-side with the real thing, you still know the difference.