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Soulsby Synthesizers Atmegatron

8‑bit Monosynth
Published June 2014
By Paul Nagle

Paul Soulsby's debut product is a small synth of violently unrestrained character.

No matter how many carefully researched, precision‑manufactured, glistening chunks of music technology come along, I still get the greatest buzz from those that dare to be different. Soulsby Synthesizers' first product, the Atmegatron, contains more buzz than a Jiffy bag from Ann Summers and is as daring as a fox at a Tory conference. Its synthesis is brash, 8‑bit digital and monophonic and if you don't mind a spot of DIY, you can save cash by buying it as a raw PCB to build into a case of your choosing. Given my woeful DIY abilities, it's fortunate that Soulsby sent a prototype of the pre‑assembled version.

Geek Chic

With its prominent Function and Value dials, surrounded by red LEDs and mystical symbols, the Atmegatron walks a fine line between school science project and alien artifact from Blake's Seven. The opaque encircled dials toggle in colour between red and green like the eyes of a psychedelic owl. They're joined by eight regular knobs and a button that's either red or green — the Atmegatron is not a synth optimised for the colour‑blind! Four of the knobs slip into alternate modes at the push of the button.

'Metal box with wooden end cheeks' is fast becoming a popular small format and, despite a few imperfections in the wood and an unpainted bottom panel, I found the quality good for a prototype. The creamy white paint job and coloured text are pleasantly memorable and, given this isn't the final model,it would be unkind to criticise the slightly loose knobs, especially as the issue was quickly remedied by a few blobs of Blu‑Tack.

Of all the controls, only the volume and bass boost are analogue and therefore theirs are the only values not stored in a patch. Bass boost adds 6dB of gain to a low‑shelf filter for extra oomph when required.

MIDI In and Out are provided, plus a slender 'programmer header' slot, about which more anon. There's a mini‑jack headphone socket, a regular quarter‑inch output and a connector for the included 12V power supply. Careful inspection will reveal a tiny MIDI indicator LED and an equally tiny switch to flip between MIDI reception and programmer mode.

Digital Dirtbag

The Atmegatron has 32 factory waveforms, six user waves, a choice of 15 digital filters, an LFO, an arpeggiator and a bit‑crusher. All these resources exist in the 8‑bit digital realm where everything is chewy, crunchy and wonky. I realised just how wonky when I found the icon for 'patch select' (a floppy disk) and toured the 16 factory sounds for an instant '80s computer game nostalgiafest.

Any sound can be overwritten, edited by a combination of knobs and encoders. Turning the left-hand dial selects the parameter to concentrate on; its value is updated by turning the right. The LED collars are effective but best viewed directly. They're not quite so clear when seen from an obtuse angle — my own preferred studio position.

The filter cutoff and resonance controls don't switch functionality, but through the rest you have fast access to distortion, modulation amounts and envelope depths. The encoders are required to set each stage of the two envelopes and as an inveterate envelope fiddler, I'd really have appreciated instant access to these. Almost at once I discovered a solution, in the form of external MIDI control. A fair percentage of the synth parameters already have dedicated MIDI CCs, including most of the amplitude envelope and apparently the rest will be added in the near future. I defined what I could to a hardware controller and was content to tweak from there.

The factory waveforms are split into two banks, red and green. To audition each in its most natural state, I switched off the filter and Wave Crusher, then zeroed the bass boost and distortion. Without coloration, the waveforms bristle with 8‑bit attitude. Whether it's the intimidating square wave or the sine with an eerie high‑end sparkle, none could remotely be described as pure. Most aren't even house‑broken. Early contenders for favourites were 'Sine+Harmonics (PPG)' or 'Pulse (CZ101)', while the various PPG bells and metallic waveforms were all coughed up with a helping of broken glass.

Additional methods for weirding‑up any waveform include 8‑bit pulse-width modulation. The Atmegatron considers all waveforms eligible for this treat, but don't expect the output to resemble PWM in its regular chorus‑like form. All become more erratic and even the noise waveform is fair game, its demented snarl becoming a glitched demented snarl. It's also possible to turn the PWM depth knob into a manual pulse‑width control. Out of the 15 LFO waveforms, one is static and when this is selected, each of the LFO-modulation depth controls are turned into DC offsets.

The Atmegatron's back panel features five‑pin MIDI I/O ports, a mini‑jack headphone output, a quarter‑inch audio output, the programmer header slot, via which the synth can connect to a computer, and an input for the external 12V power supply. The Atmegatron's back panel features five‑pin MIDI I/O ports, a mini‑jack headphone output, a quarter‑inch audio output, the programmer header slot, via which the synth can connect to a computer, and an input for the external 12V power supply.

There's plenty of mileage in the included waveforms and from user waves too, which we'll look at soon. What happens to these sources depends on which of the 15 bad‑tempered filters you choose — and hardly any of them are fully predictable. Admittedly, the low‑pass filter does roughly the same job as a conventional filter, with the exception that resonance is more wayward. Its filter sweeps are performed with filthy wire brushes — but sound great! Other components add extra layers of dirt and the filter's normalise mode is crucial in reigning in the excesses of distortion. It reduces the waveform's level on entering the filter and boosts the whole shebang on exit, thus making the most of the available bits.

I found the high‑pass filter an instant hit. It spewed forth wicked — actually borderline evil — oscillator sync‑like tones when given metallic waveforms to chomp on. The most smooth and tailored responses of the collection are produced by the resonance‑free Butterworth and Bessel filters, while the notch filter is also rather benign and subtle. The remainder are an assortment of rough and ready parametric equalisers loaded with varying amounts of boost, some quite radical and extreme. They wrench characteristics from waveforms that are otherwise only hinted at. Distorted vocal tones spill forth as easily as trashy, aliased basses and bright high-end sequencer fodder. Incidentally, for lovers of sequences, the envelope decays are linear and therefore not especially zappy. A future OS alternative promises to add an exponential response, most likely at the expense of other features.

More Filth

Adding the smallest amount of distortion can be quietly transformational, but further up the scale it gets overblown fast. Distortion at its max is a roaring, gnashing monster capable of making instant elbow room in a mix, but even that isn't the Atmegatron's last word in horror. That honour goes to the Wave Crusher, a combination of bit reduction and sample-rate reduction, or rather 15 different combinations, each with a different stench of nastiness.

We're almost through the grime now because, despite being armed with some wild and twisted waveforms such as 'Duh Dugga' and 'Dugga Duh', the LFO is straightforward enough. It syncs automatically to incoming clock (the division rates are printed on the panel) and can rhythmically modulate the filter cutoff, amplitude, pulse width and phase. Modulation of phase is interesting; it has a slight blurring effect on the output and, although I wouldn't call it soft or warm, the effect is phaser‑like. When you deactivate phase modulation, the shift in clarity is sudden and striking.

I should quickly mention portamento because you're given the rare choice of a glide time that is either constant regardless of the musical interval, or proportional to the interval played. In the latter case, notes close together exhibit almost no glide at all. This leaves just the arpeggiator to tinker with. It has 15 pattern choices and clock divisions equivalent to those of the LFO. Patterns of up to 16 notes run either forwards or in ping‑pong mode and the arpeggiator will cheerfully simulate the technique 8‑bit computers used to hint at chords, which involved playing its notes very fast.

My Mind Is Going

There seems to be a spirit in the 8‑bit world that demands the maximum return from every bit, so how better to do this than reinvent yourself completely? As I type, there are three replacement Atmegatron personalities, each a work in progress with extra features planned.

Before checking these out, some software must be installed; Arduino, which runs on Windows, Mac and Linux. This open programming environment is accessed via the programmer header slot on the rear panel. As long as you have a USB TTL serial cable (the manual explains all), it's just a matter of flicking the tiny switch to enable USB transfer and then uploading the chosen identity. The process takes about 20 seconds, and if you've stored any patches in the Atmegatron, backing them up via a SysEx dump prior to doing this is essential.

I fired up Atpolytron first. After all, paraphony is finding its way everywhere these days, so why not into an 8‑bit digital synth? Four voices are created by a divide‑down process that demonstrates some of 8‑bit's unique charms, not least being that no voice is exactly in tune. Although Atpolytron lacks the presence of the original Atmegatron (and doesn't feel as stable yet), it played well for unusual pads and textures.

Next up, Atcyclotron is a wavetable synth ideal for drilling the enamel from your teeth or being a very insistent single digital voice. By sacrificing the Atmegatron's filter, Atcyclotron can offer four different waveforms, each sampled in turn to produce a unique composite wave. The regular filter controls determine the amount of each waveform's contribution and if you're wondering how that actually sounds, think 'punk PPG'. It is unashamedly spiky, angry and, even though a work in progress, is capable of some startling noises.

Last but not least, Atmegadrum is a drum machine with 16 different samples and 16 steps on which they can be placed. Control over each drum is limited to level adjustment right now, but Atmegadrum already has a distinctive and likeable 8‑bit edge — hopefully there's more to come.

Overlays are available to be printed as helpful reminders of the changed functionality and upon fitting my first, I realised why it can sometimes be handy to have loose knob caps.

Conclusion

If your life is a sacred quest to make music so slick it licks the porcelain cheeks of perfection, I expect I lost you at '8‑bit'. If, however, you're open to the possibility that a spot of dirt can encourage musical pearls to form, spare a thought for the unassuming Atmegatron — it's loaded with the stuff! A synthesizer that is blatantly trashy in a world awash with squidgy and analogue, the Atmegatron's hard, brittle tones can be ignored in the same way a paper bag can ignore a chainsaw.

This is not a typical monosynth. Sometimes it isn't a monosynth at all. Of the alter egos currently in development, all have something interesting to offer. Perhaps the Atmegadrum is the most initially promising, but since all are open source it's early days yet. With its distinctive 8‑bit nature and potential still to be explored, the Atmegatron is a lot of synth for not very much money.  

Alternatives

Commercially available 8‑bit hardware synthesizers aren't exactly thick on the ground and those that come to mind tend to have nasty oscillators tamed and restrained by the inclusion of analogue filters. There's the MeeBlip Anode or the Oto Biscuit with its 'Der Oto' personality loaded, but these are honey and butter compared to the Jet Set Willy‑style bleeps, gnashes and warbles of the Atmegatron.

Editor

The Atmegatron editor is the best way to see multiple parameters at once, plus it features a waveform designer to populate those six user waves. You can hand‑draw waveforms, generate random waves or pick a number of synth standards with a click. If these techniques don't appeal, very short mono samples (less than 1000 samples long) can be imported.

As well as editing the LFO, envelopes and arpeggiator visually, the editor serves to quickly populate a bank of 16 patches, writing them directly to the synth.

Published June 2014