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WS Audio Trueno

Analogue Synthesizer
Published July 2018
By Gordon Reid

WS Audio Trueno

If good things really do come in small packages, this USB stick-based analogue synth ought to be a winner.

Synthesizers started out as large lumps of discrete analogue components that weighed a lot, cost a lot and often sounded great. Then someone invented the integrated circuit and they weighed a lot less, cost a lot less and less often sounded great. Next came the microprocessor, first used to control the synthesizer, then to generate many of the control signals within the synthesizer, and then to generate all of the signals within the synthesizer. After that, it wasn’t a huge leap to dispose of any dedicated hardware and to run the synthesis algorithms on a personal computer. But then the backlash began, and while people still wanted to use their computers to control their sounds, many wanted those sounds to be generated using a new generation of large lumps of analogue components. This was all very well, but where could you turn if you wanted access to analogue sounds in tiny studio spaces or while passing the hours on transatlantic flights? After all, you could hardly ask the person in the next seat to hold your Moog IIIC while you doodled the hours away en route to JFK. So someone had the idea to dispense with the type of hardware that could anchor a medium-sized yacht in a mild storm, and created a tiny analogue/digital hybrid synth embedded in nothing more than a large USB stick. His name is Will Shaw, and he created WS Audio to manufacture and sell his solution: the Trueno.

The Architecture

The Trueno comprises two elements. The first is the USB stick [shown above] that houses the analogue hardware: three oscillators, a dual-mode filter and an output amplifier. Around twice the length and twice the width of a traditional memory stick but weighing just 25g, it’s the synth that you can take anywhere and lose through a hole in your pocket. The second element is an editor implemented as a VST2, VST3 and AU plug-in as well as a stand-alone application, and this performs as a sound generator (three digital oscillators), as the source of all of the control signals (including the LFOs and contour generators), as an effects processor, and as an audio recorder.

The three analogue oscillators each generate the standard litter of analogue waveforms: ramp, pulse (with variable pulse width and PWM on Osc 1, and fixed square waves on Osc 2 and 3) and triangle. Each also offers controls for pitch offset (±24 semitones), fine-tuning (±1 semitone), and output level, as well as an on/off switch that, when ‘off’, seems to reduce the output level of any given oscillator to its minimum, allowing a low level of signal to bleed through.

If you step through the representations of the analogue waveforms in the editor and keep going, you’ll come to the Trueno’s digitally generated, 8-bit, 64-partial additive waveforms. In addition to digital noise on Osc 3, these comprise 256 waveforms including 25 basic waves, 21 bass waves, 19 bell waves, three bssn (bassoon?) waves, 17 buzz waves, five clarinet waves... right the way through the alphabet to the single xylophone wave. But these don’t define the full range of waves obtainable, because clicking on the small ‘s’ in the upper right of the waveform display takes you into spectral mode, which allows you to display, zoom in and out of, and edit the partials determining the wave. Your control over the partials is at best coarse and, with all of them set to zero, there’s residual output when there should be none, but many owners will find the system to be great fun as a source of sonic serendipity. Will Shaw has described these oscillators as “endearingly lo-fi, with plenty of aliasing”, and he’s not joking. The digital signals (which are coarse to start with) are converted to analogue audio using a lo-fi DAC, and sounds based upon them take me back to an era when things that went beep almost always did so with a halo of noise and lots of spurious high frequency artifacts.

Whether you choose to use the analogue or digital oscillators, or even a combination of them, there are three modulation options within the oscillator section. The first of these employs Osc 3 to modulate the amplitude of the output from Osc 1, the second employs it to modulate the width of the Osc 1 analogue pulse wave, and the third employs it to modulate the filter cutoff frequency. Unfortunately, Osc 3 is permanently connected to the pitch CV, so you can’t use it to create consistent effects as you play up and down the keyboard, and it lacks a low-frequency mode, so you can’t create the usual range of PWM sounds. Strangely, a tracking, audio frequency modulator is most useful when creating cross-mod (FM) sounds, but that’s the option that’s not available — you can’t use Osc 3 to modulate the pitch of Osc 1. Furthermore, there’s no oscillator sync, and no way to sweep the pulse width using an envelope, all of which means that, while flexible in some areas, the Trueno’s oscillator section is quite limited in others.

The Trueno editor software.The Trueno editor software.

The Filter & Amplifier

The outputs from the oscillators are mixed before being presented to the Trueno’s dual-mode (low-pass and band-pass) 12dB/oct analogue filter. Like the Polivoks filter on which it’s based, it’s aggressive, unstable and coarse which, depending upon your taste for such things, isn’t necessarily a bad thing. However, this type of filter can also suffer from excessive noise and bleed, and so it proves here. Whether you view this as a fault or characterful is your choice.

Alongside the mode selector and the cutoff and resonance controls, the editor offers a key follow on/off switch and the controls for the filter’s dedicated ADSR contour generator. Manual control over the cutoff frequency is quantised to approximately semitone steps, which is a characteristic of 7-bit MIDI, but filter sweeps generated by the contour are smooth. Given its provenance, I wasn’t surprised to find that the filter doesn’t oscillate at maximum resonance, although it gets close. With all of the oscillators switched off, you can hear it shaping the residual noise, and playing this demonstrates that it doesn’t track at precisely 100 percent, which is a shame but not unexpected. After the filter, the signal reaches the audio amplifier, the gain of which is controlled by a second ADSR contour generator.

Four assignable ADSR contour generators and four assignable LFOs provide additional shaping and modulation. These are quite flexible; the contour generators each offer a linear/exponential curve option, a release on/off option and a bi-polar amount control, while the LFOs each offer five waveforms (including noise/S&H), with additional controls for frequency and bi-polar output level, initial phase position, MIDI Clock sync and key triggering on/off. You route their outputs to the desired destinations using the little boxes that you’ll find above each of the rotary controls in the oscillator, filter and amplifier sections. Just click on the selected contour or LFO and drag it onto the destination, and the connection is made. You can now click and drag inside the destination box to determine how much of the source is applied, and with what polarity. In all cases, contour amounts are shown in pink and LFO amounts are shown in orange, but I would have chosen colours further divorced from one another to make the distinction clearer. With eight sources and 18 destinations, it’s a reasonably flexible architecture, although none of the contour generators nor LFOs can modulate one another, which is a shame.

At this point, the audio signal passes through a 24-bit, 44.1kHz DAC so that it can be presented to the three digital effects processors in the Trueno software. First comes the modulation effects (flanger, phaser, 4-voice chorus and 8-voice chorus) section, which has a dedicated LFO with rate and depth controls, plus controls for feedback and mix. Next comes a delay section with mono, stereo and ping-pong modes. This provides control over the delay length and feedback as well as the mix of the original and delayed signals, and there are three filter modes for damping. The delay time is available only as quantised ratios of MIDI Clock and, even in stand-alone use, there’s no way to set this in milliseconds, but there must be an internal clock because the delay runs without being synchronised to MIDI. The maximum gain of the feedback loop is unity, which means that you can create endless loops, but not the sci-fi effects that you can obtain from delay lines with gains greater than this. Finally, there’s the reverb unit, which offers the same set of controls as the delay, but with the reverb time calibrated in arbitrary units from zero to 100. Unfortunately, I found that invoking the effects reduced the loudness of sounds, which wasn’t ideal and, while they are adequate, I would probably choose external effects in preference to them.

Other Bits’n’bobs

The remaining facilities are contained in two sets of controls found in the top left and bottom right corners of the editor. Those at the top include master transposition (±24 semitones) the glide mode (constant time and constant rate, both with legato and non-legato options) and the glide time. A fourth control chooses between monophonic mode and a three-voice paraphonic mode in which oscillators 2 and 3 are slaved to oscillator 1’s settings but can be played with independent pitches.

Those at the bottom include the MIDI indicator (which doubles as a Panic button), the USB indicator (which connects and disconnects the Trueno hardware) and the tuning button. You’ll find it necessary to click on the last of these a few times as the hardware reaches its stable operating temperature or significant weirdness will result! This is also where you’ll find the fields that allow you to direct pitch-bend, velocity, aftertouch, and MIDI CCs to the destinations of your choice, with the amount of your choice, and with either polarity. Not all of the voicing parameters can be controlled in this fashion, but there’s nonetheless a significant amount of automation available here, especially since controllers can be directed to multiple destinations simultaneously.

The final control is perhaps the strangest. This allows you to choose a destination folder and record the Trueno’s output as a WAV file at sample rates ranging from 44.1kHz to 96kHz. Having done so, you can then drop the resulting file into your DAW for editing and mixing. Happily, I was also able to record its output in the usual fashion within Reaper. I placed an instance of the Trueno application in track 1, connected it to the Trueno hardware, generated a MIDI sequence and then recorded the Trueno’s output without any need to render externally and then import. I don’t know whether this will work universally — I was unable to achieve the same success in Digital Performer — but there’s at least one DAW that will allow you to sequence and record the Trueno in the conventional fashion.

In Use

My first impressions of the Trueno were very positive; the packaging and presentation are first class, and the body of the Trueno itself seems to be milled out of a single block of aluminium and then blasted to give it a classy feel. But, given that it was designed to be a convenient way for computer users to obtain analogue sounds, it’s a shame that it’s so wide. It will obscure two USB ports on many laptops, so you may need to use it at the end of an extension cable or inserted into a USB hub. However, this might create its own problems, not least because the stick draws 480mA, which is close to the 500mA limit of USB2 and means that you’ll probably need to use a powered hub, which then adds a wall-wart to the equation. Somehow, a USB synth stuck into a powered hub at the end of a cable doesn’t sound nearly as attractive as a USB synth inserted directly into your computer. Another thing that might frustrate users is the lack of an analogue output. I can see how this might have been difficult to implement, but it would have made the Trueno a much more attractive proposition.

WS Audio TruenoTurning to the editor, I think that opinions about its GUI will be divided between those who find it clean and functional and those for whom it represents the antithesis of analogue feel. But to give credit where it’s due, it’s a clever design that contains everything in a single small window so you don’t have to contend with multiple pages or menus. It’s also worth noting that, while you can launch the application multiple times simultaneously within a suitable host, only one instance can be connected to the stick at any given time. Perhaps a future development would allow you to launch multiple applications to control multiple sticks, but there’s no hint of that at the moment.

Moving on to its sound, the Trueno can burble, scream and shriek, and can sound bloody unpleasant if you allow it to do so. Some people will love this. Over the years, much of the danger has been polished out of analogue synthesis and, in that respect, the Trueno reminds me of some of the synthesizers of my youth. Nonetheless, a little perseverance also revealed a full palette of softer and more conventional sounds. Dialling back the oscillator levels and the filter resonance, I was able to produce all manner of civilised patches spanning the spectrum from orchestral imitations to lead synth sounds. I was even able to create patches that imitated synths such as the ARP ProSoloist and the Roland SH-2000 by directing aftertouch simultaneously to destinations such as the modulation depth, brightness and loudness. This then led to many more sophisticated modulation experiments using MIDI CCs to affect numerous other aspects of the sound.

I also found that the Trueno excels at bass sounds. Setting up a triple-oscillator bass patch, overdriving the filter input and sweeping the low-pass filter mode at high resonance could be a thing of joy. Mixing the analogue and digital waveforms was also a source of happy experimentation. Nonetheless, the filter and amplifier can exhibit strange anomalies. For example, there were times when I tried to create sounds with instantaneous attacks followed by a bit of decay to a moderate sustain level, yet obtained a distinct ‘glug’ at the start of every note. It took me a long time to discover that this was a consequence of the contour amount being too high; once I reined this in, all was as it should be. I also obtained some odd results when passing noise through the filter, but whether you treat these as happy accidents that can lead to serendipitous sounds or errors that stop you achieving the results you want is again up to you.

My final tests involved the paraphonic mode. I was able to create some unusual sounds using this, although I had to be careful to keep the signal levels low to avoid distortion. Unfortunately, whether in monophonic or paraphonic mode, I found that the Trueno could generate glitches. I eventually discovered that I could eliminate these by choosing different combinations of buffer sizes and output sample rates, and by leaving the internal effects switched off. This implies that something in the system is running out of time, so there’s still a bit of work to be done here.

A subset of Trueno voicing destinations in Reaper.A subset of Trueno voicing destinations in Reaper.Before the end of the review, I looked at the automation that I could obtain within Reaper, and was stunned to find that (as far as I could tell) every voicing parameter is available as a modulation destination. This includes the waveforms themselves (which suggests some interesting possibilities for wavetable synthesis) and even the individual partials within each of the digital oscillators. Although the results could be rather erratic at times, I could spend months experimenting with this!


It glitches. It burbles. It doesn’t always do what you ask, and it suffers from bleed-through and noise. But monosynths that can be brash, uncivilised and rude have an enduring appeal, and there’s something rather endearing about the Trueno’s ability to create raw sounds that walk the knife-edge between unusable and inspirational. It won’t appeal to the mainstream of keyboard players, and many will see it as a bit of a gimmick; after all, we’ve had MIDI-controlled synth modules since 1984.

So the novelty of the Trueno lies in its size, and for those people who work almost exclusively within a computer — often a laptop for portability — it could prove to be both a source of conventional sounds as well as some that, I think it’s safe to say, are unlikely to emerge from a plug-in. You could argue that a USB stick, small though it is, isn’t ‘in the box’, but I think that that’s quibbling. You could also argue that it lacks something that many players regard as a prerequisite of analogue-iness — a physical control surface. But some highly respected vintage analogue synths lack knobs and sliders, so that’s a red herring too.

So, where does this leave us? To be honest, I don’t know. Some people might hail USB stick synthesizers as the future, while others will claim that they’ll be of no great consequence. But however you view the Trueno, one thing seems certain; once its teething problems are eliminated, it will be the most cost-effective way to obtain a hybrid synth with three analogue (or digital) oscillators, an analogue filter, four LFOs, six contour generators and extensive automation. It could flop horribly, or it could be the surprise success story of 2018.  

Running Trueno On OS 10.9 & 10.10

The Trueno software was originally developed for OS 10.11 onward and Windows 8 onward. You can also make it run on OS 10.9 and 10.10 if you’re prepared to use Terminal to run a file found on the installation disk, and then run a sudo command to disconnect a kernel extension that blocks the Trueno software from connecting to the hardware. This doesn’t always work if other applications are using that extension so, if this proves to be the case, you’ll need to close the conflicting applications and try again. It can be a bit frustrating, but it works. In contrast, there’s no backward compatibility with Windows 7, nor will there be.

Latency & Sampling Rates

WS Audio TruenoThe Preferences window shows that the new v1.1 software offers re-sampled audio rates ranging from 44.1kHz (which is the Trueno hardware’s clock rate) up to 96kHz, and that its latency can be as low as 32 samples. You may wonder why there are two buffers (called Vectors) shown.

The first is the software’s audio interface buffer, while the second is the hardware synth’s buffer. So, for example, if the I/O buffer is set to 32 samples and the synth’s is set to 16, the Trueno will generate two synth buffers before the audio is sent onward from the software. This is weird, and appears to be a consequence of WS Audio using some ‘off the shelf’ audio interfacing software as part of the underlying architecture.

Patch Management

WS Audio TruenoAlthough I started this review using v1.0 of the Trueno editor, the beta version of v1.1 appeared part of the way through. Perhaps the most significant update in this was the addition of patch saving and recalling, together with a bank of 39 factory patches. In principle, this allows you to save and load individual patches as well as complete banks of sounds. All of this worked, although I was unable to make new sounds appear in an existing bank, which also should have worked but didn’t. Since I was using a beta version I imagine that the problem will have been eliminated by the time that you read this. You’ll also find a useful Init patch under the file menu. This sets all of the voicing parameters to sensible initial parameters so that you can start programming new sounds from scratch.

Published July 2018