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UDO Audio Super Gemini

Polyphonic Synthesizer By Rory Dow
Published March 2024

UDO Audio Super Gemini

If you thought the age of hugely ambitious polysynths was over, think again...

“20‑Voice Dual Layer Polyphonic Binaural Analog‑Hybrid with Super Wave Technology” is quite a description. But the Super Gemini has big ambitions. It aims — and mostly succeeds — in standing shoulder to shoulder with synth giants like the Roland Jupiter‑8 and the Yamaha CS‑80.

UDO are still relatively new to the synthesizer world. In late 2021, they released their first product, the Super 6. Inspired by the Roland Jupiter‑6, the Super 6 takes the six‑voice polysynth concept to new heights with a true‑stereo signal path and FPGA digital oscillators capable of alias‑free audio‑rate modulation. Like its principal influence, the Super 6 offers a hugely tactile user experience, with physical controls for nearly every parameter.

The Super Gemini takes the Super 6 and doubles it. You get two layers of the Super 6 engine, known as the Upper and Lower layers. True to UDO’s desire to keep things tactile, each layer has a complete set of duplicate controls on the front panel. The Upper layer has white fader caps, whilst the Lower layer uses a fetching orange. Of course, that’s not the end of it. UDO have added plenty of additional features to harness the extra power.

It’s A Beast

The instant reaction to the Super Gemini is, “Whoa, it’s big.” At 1040 × 440 × 110mm, it will be one of the larger keyboard synthesizers in any rack. While there are plenty of five‑octave keyboards in the synth world, it’s the depth that adds extra size, and that’s because of the dual set of Super 6 controls for each layer and the new ribbon controller. The keyboard supports poly aftertouch, too, which is a lovely addition.

The overall build quality is superb. It’s a beautiful design, whatever angle you look at it from. The white, grey and orange colour scheme is right up my street. I’m also glad to see that the overhanging keys from the Super 6 have gone. They could prove a roadie’s nightmare.

Round the back is a nicely recessed panel for the various connections, including stereo mix outputs, stereo upper and lower layer outputs, MIDI In, Out and Thru, a USB Type‑B connector for MIDI and file management, and four pedal/CV inputs for sustain, expression, volume and delay freeze (more on that later).

Round the back we find everything you’d hope to find on a large polysynth like this: an IEC mains cable input for the built‑in power supply, full‑size MIDI In, Out and Thru ports, a USB B port, quarter‑inch jack sockets for the four(!) pedal inputs, a stereo mix output and separate stereo outputs for each layer.Round the back we find everything you’d hope to find on a large polysynth like this: an IEC mains cable input for the built‑in power supply, full‑size MIDI In, Out and Thru ports, a USB B port, quarter‑inch jack sockets for the four(!) pedal inputs, a stereo mix output and separate stereo outputs for each layer.

Super Twins

As briefly as we can, let’s recap the Super 6, because each layer of the Super Gemini is essentially a Super 6 with tweaks. I reviewed the Super 6 in the December 2020 issue and won’t go into the finer points here, so I refer you to that original review if you want the full details.

The Super 6 synth architecture comprises two ‘DDS’ (Direct Digital Synthesis) oscillators, two filters, two envelopes, two LFOs, a delay, a chorus, an arpeggiator and a sequencer, all doubled on the Super Gemini. Probably the most significant Super 6 feature is Binaural mode. When engaged, the entire synth works in true stereo, with the signal path — oscillator, filter, amp and effects — having duplicate voices for each stereo channel. In the Super Gemini, each layer can be switched to Binaural mode independently, which is true of most features, as the two layers are independent.

Binaural mode halves the number of voices available, but creates some superb sounds. The Super Gemini can generate 20 mono voices or 10 Binaural voices. So, when using it in Dual or Split mode, you’ll get five voices per layer, one less than the Super 6.


The first oscillator — DDS1 — can operate in Super mode, which offers seven unison copies of either standard analogue‑type wave shapes or one of 16 single‑cycle waveforms. The second oscillator — DDS2 — cannot do unison or single‑cycle waveforms, but offers pulse‑width modulation on its square waveform and a selection of more normal analogue shapes. It can also double up as an LFO, or as a sub‑oscillator phase‑locked an octave below oscillator one.

DDS1 is where we find the first of the Super Gemini’s audio engine upgrades: wave morphing. You can assign any of the 16 waveforms to Wave A and B, and then morph between them. The Super 6, by contrast, can only play back a single static waveform. Morphing can be automated using LFOs or envelopes, and is available as a modulation destination in the matrix. This is a significant update to the oscillator. It’s a shame it’s not a full wavetable, but it’s welcome nonetheless.

A ‘DSS Modulator’ section offers a wealth of oscillator modulation options, including controls for DSS1’s Super mode, dedicated controls for LFO and envelope pitch modulation, and the fantastic Cross Mod, which uses DDS2 to frequency‑modulate DDS1. In my original Super 6 review, I did remark that the pitch of DDS1 will move as more cross‑modulation is applied, which means that patches could be out of tune with no way to correct them. This is because Cross Mod uses exponential FM, which changes the pitch of the carrier wave. I’m pleased to see two new ways to retune on the Super Gemini. The Lower Layer has a dedicated Detune control to detune the entire layer relative to the Upper Layer, and a Performance preset also has a Detune option. So, if you’re doing static cross‑modulation, you can retune quite easily.

Other ways to cross‑modulate the oscillators are hard sync and ring modulation. The latter is also new to the Super Gemini and is an excellent addition, especially if you want to recreate classic synth sounds. The vast potential when combining cross‑mod, sync, unison and ring mod is not to be underestimated.


The filters are an analogue, low‑pass, 24dB‑per‑octave SSI design based on the classic SSM2044 chip used in the PPG Wave 2.3. They have a lovely resonant character, although some bottom end is lost when adding resonance. This can be mitigated somewhat with the filter drive setting. It’s also possible to apply frequency modulation to the filter from DDS2, and it sounds fantastic.

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