Over the last few years, Audio Damage have built a reputation as seriously eclectic developers, releasing everything from versatile effects to modeled emulations of vintage gear. For Phosphor, Audio Damage have chosen one of the less obvious early '80s synths to emulate.

With most of the classic synths already recreated in software form, it's becoming increasingly difficult for software developers to find inspiration for retro-inspired products. The Syntari Corporation's alphaSyntauri may not be a household name, but it played a major role in bringing digital synths to the consumer market.

Just like the alphaSyntauri, Phosphor employs a relatively simple architecture consisting of two wavetable oscillators (each with its own envelope generator) and two LFOs for modulation.

Rather than generating a harmonically rich square, triangle or sawtooth wave and then stripping away harmonics by filtering the signal, additive synths construct harmonically rich waves by adding together partials sine wave harmonics of the fundamental frequency - in order to build up the sound. Phosphor's uncluttered interface belies its extremely flexible sound engine. In comparison to more modern additive synths, 16 partials may seem like it could restrict the synth 's sonic range but, flicking through the presets, any fears are quickly allayed.

It's impressive to hear just how wide Phosphor's scope is - from warm bass to filthy leads, cold digital pads to clean organs and keys, the plug-in proves adept at just about any task.

By default, Phosphor's output is significantly cleaner than the sound produced from the alphaSyntauri's 8-bit MusicSystem cards. However, if you're looking for a real taste of '80s digital grime, tiny Space Invader-style buttons enable a vintage lo-fi mode for each oscillator and control section, introducing aliasing and grunge to the signal and allowing the synth to offer an even more realistic impersonation of the original. It's a great option, adding grit and dirt to the sound without the need to resort to placing a bitcrusher or overdrive in the signal chain. The addition of a stereo delay section also allows for some handy echo processing, with each oscillator being fed to its own delay line and cross-feed back options to create ping-pong effects.

Most of us are so familiar with analogue-style subtractive synthesis these days that any other method seems alien at first. As a result, judging Phosphor's ease of use objectively is slightly tricky. Editing is certainly nowhere near as complex as FM synthesis or as overwhelming as modular synths can be, but it does take a bit of getting used to the idea of building up sounds from partials rather than using filters to strip them down.

Phosphor's filters only affect the wet outputs of the delay lines, so the overall sound depends primarily on the oscillator settings. Unlike most additive software synths, the alphaSyntauri didn't allow the levels of individual partials to be automated and, likewise, Phosphor relies on the envelope generator to control each oscillator's overall amplitude rather than allowing each oscillator's harmonic content to change over time.

It soon becomes apparent that the smallest tweaks of the two oscillators and their respective envelopes can lead to complex, evolving timbres as the harmonic content of the output changes dramatically. The key to creating shifting, evolving sounds with Phosphor lies in setting slightly different amplitude envelopes for each oscillator and taking advantage of the various LFO modulation options. The cross-modulation options in particular are incredibly effective for creating interesting sounds. Go overboard and you'll end up with viciously aggressive distorted sounds and metallic frequency modulation effects, but apply just a smidgen of cross-mod to one or both oscillators and you'll easily find a sweet spot. It shouldn't take long to get the hang of the way the sum of the two oscillators is crucial and understand that even the most subtle adjustment of certain settings can have a dramatic effect on the overall sound.

Inevitably, Phosphor raises the question of whether a couple more tweaks to the alphaSyntauri concept would have made the plug-in easier to use, better sounding or more versatile. The addition of a traditional analogue-style filter would undoubtedly make editing easier for users familiar with subtractive synthesis, but it seems to me that it would be missing the point of the synth to turn it into an additive/subtractive hybrid. If you're looking for a plug-in, of that nature there are plenty of options already on the market and to add subtractive options would dilute the authenticity of the emulation.

Overall, I only have one significant complaint about Phosphor: the LFO waveshape controls are seriously useful, allowing the shape of the LFOs' output to be skewed and adjusted, but it would be nice to have a visual indicator of the resulting waveform. It's not always easy to understand exactly how the control works without referring to the diagrams in the manual.

Phosphor is a surprisingly versatile synth which is capable of producing some truly unique sounds along with a broad range of staples. The editing system may initially seem unfamiliar to subtractive synth fans, but the simplicity of the layout and impressive power of the modulation options make it easy get to grips with creating sounds. Audio Damage have stayed true to the spirit of the original alphaSyntauri. With a highly useable set of 80 factory presets and a very reasonable price, Phosphor is a refreshing alternative to the hundreds of VA soft synths on the market.

In 1980, the vast majority of synths were analog. The first mass-market digital synths were still a few years away, while the majority of sample-based instruments such as the Fairlight and Synclavier were expensive for all but the most wealthy musicians.

The Syntauri Corporation's alphaSyntauri offered a much more affordable alternative to the astronomically-priced exotica. Rather than developing a fully custom hardware processing unit, the company instead chose to turn to the recently released Apple II Plus computer and its eight expansion card slots. Announced in 1979 and released the following year, the alphaSyntauri setup offered 16-note polyphony, patch memory and velocity sensitivity, while later software updates would also add 16-track sequencing, score editing and user-drawn waveforms.

The Apple was at the heart of the system, running the Alpha Plus software which interfaced with Mountain Computer's Music-System 8-bit audio expansion cards. At $1,500, the alphaSyntauri still wasn't cheap, but it undercut the likes of the Synclavier and PPG 's early digital synths by many thousands of dollars. Alongside Passport Designs' Soundchaser and Crumar's GDS and Synergy, the alphaSyntauri takes its place as one of the unsung heroes of early digital synthesis.