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Waldorf Iridium Keyboard

Waldorf Iridium Keyboard

The keyboard version of the desktop version of the Quantum, is the Iridium Keyboard even better than the original synth?

In our April 2019 issue, Gordon Reid reviewed Waldorf’s ambitious new flagship instrument, the Quantum — a hybrid analogue/digital synthesizer capable of wavetable, granular, sample playback, physical modelling, virtual analogue, and even speech synthesis.

A year later, Waldorf announced the Iridium, a synthesizer based on the Quantum architecture. Instead of eight analogue/digital hybrid voices, it had 16 all‑digital voices. The Iridium was a desktop device which replaced the Quantum’s five‑octave keyboard with a 4x4 set of MPC‑style drum pads. The pads were met with mixed reviews, mainly because they weren’t velocity or pressure sensitive, but the general concept of a 16‑voice, all‑digital flagship seemed like a winner.

So Waldorf have followed up with a keyboard version of the Iridium, which we are reviewing here. The Quantum and Iridium keyboard share a similar hardware design and an almost identical sound engine. They even share presets.

The front panel retains the full‑colour touchscreen at the centre, surrounded by the most useful controls for oscillators, filters, envelopes, LFOs and effects. Waldorf have taken the opportunity to tweak the layout. For example, the Iridium adds more knobs to accommodate the dual digital filters but loses the Quantum’s dedicated Komplex modulator section (the Komplex modulator itself remains accessible through the touchscreen). The Iridium also adds a column of Macro buttons that can be programmed for various tasks.

The Quantum’s semi‑weighted five‑octave Fatar keybed with channel aftertouch is replaced by a new four‑octave design with polyphonic aftertouch. The addition of polyphonic aftertouch is most welcome. Because it’s one octave shorter, the Iridium is more compact than the Quantum, measuring 851 x 355 x 110mm and weighing 14kg. The Quantum measures 1006 x 401 x 131mm and weighs 17.8kg — a not insignificant difference.

How Many Synthesis Types?

Let’s recap on the capabilities of the Iridium and Quantum. There is much common ground so we won’t duplicate everything from Gordon’s Quantum review, but we’ll cover the important stuff. Waldorf have added some new features since the Quantum review, which are also available in the Iridium. We’ll make sure to cover those too.

An Iridium/Quantum patch has two layers. Each layer is a complete synth patch which can be stacked, key‑split, panned, and you can assign the number of voices for each layer. You can even play them bi‑timbrally by assigning different MIDI channels to each layer. Sadly, where the Quantum had two sets of stereo outputs, the Iridium only has one, so the two layers cannot be processed separately. Why, Waldorf, why?

Layers comprise three oscillators, three multi‑mode filters, six envelopes, six LFOs, a Komplex (multi‑stage envelope) modulator, and up to five effects. Layers are always saved as a pair (a ‘Multi’), but you can load individual layers from any patch.

The oscillators are the heart of what makes the Iridium so flexible. There are five choices: Wavetable, Waveform, Particle, Resonator and Kernels. Each of the three oscillator slots (six if you go dual layer) can load any oscillator type.

The Wavetable oscillator is, of course, Waldorf’s speciality. You get 85 factory wavetables, each with 128 waveforms. There’s plenty of sonic twistery on offer with control over the phase, spectrum, brilliance, key tracking and overdrive. Plus, you can choose from five different interpolation modes and four sonic modes, which affect aliasing and other desirable ‘vintage’ artefacts. You can also import wavetables from files or analyse a WAV file from the SD card slot. There is even a speech to wavetable synthesizer — type in any word or phrase, and the Iridium will synthesize a wavetable to ‘speak’ it.

The Waveform oscillator is a virtual‑analogue engine capable of the usual waveform types. But this being a flagship product, it doesn’t stop there. There is eight‑voice unison. Waldorf calls these voices ‘kernels’, not to be confused with the Kernels oscillator, which we’ll come to shortly. You can tune up to four kernels to make chords or intervals, with the other four being used for detuning and stereo spread. Every waveform has some form of PWM‑style waveshaping, and there is built‑in sync with its own dedicated sync oscillator.

The next oscillator type is Particle, which encompasses sampler, multi‑sample playback, and granular synthesis. There is a 1GB sample library on the internal 4GB flash RAM. Multi‑samples can be key and velocity split with individual loop points and start/end points. There’s even a full integrated mapping editor so you can create your own multi‑samples. Switching to Particle (granular) mode allows up to eight grains to be pitched, panned, enveloped and randomised in many interesting ways. You can automatically travel through the sample, which sets the base position from which the grains are taken, or you can automate it from just about any modulation source. The Particle oscillator is the key to realistic sample‑based patches and wild experimental ones.

The Resonator oscillator offers a flexible physical modelling algorithm using a noise source (or a sample) processed through resonant filter banks. Through tight control of exciters and harmonics, plucked strings, wind instruments, bells, chimes, percussion and many sounds you’ve never heard before can be achieved. There are plenty of on‑screen graphics to help you visualise what is happening. Although the physical modelling doesn’t always nail any specific instrument’s sound, it offers a unique sonic palette with which to layer and experiment.

The fifth and last oscillator type is Kernels. This oscillator type was not initially present when the Quantum was first released. To access it, you had to press a combination of buttons on the front panel for which there was understandably no label. Waldorf have updated the front panel of the Iridium to include a label for the shortcut. I’m not sure why they didn’t just add a fifth dedicated button, though.

Up to six kernels (oscillators) can be combined in an almost modular fashion. These kernels can be wavetables, VA waveforms or noise. Each kernel can audio‑frequency modulate any other kernel using a dizzying choice of amplitude modulation, frequency modulation, phase modulation, ring modulation and phase distortion. Kernels can even self‑modulate for feedback tricks. Each kernel has a multi‑stage envelope to control the kernel’s output volume. If this sounds complex, that’s because it is. To make it a little more friendly, Waldorf have included the ability to create templates with a macro page (five controls, each of which can control up to five different parameters). And they’ve included a great selection of presets to get you started. The Kernels oscillator is a huge addition to the Quantum/Iridium engine as it adds several flavours of FM and phase distortion to the already impressive list of synthesis types.

Incidentally, it’s not just the Kernels oscillator type that can save presets. All of the oscillators can be saved as a sub‑preset. Got a favourite vocal sample that you like granularised in a certain way? Just save it as a preset, and whenever you instantiate the Particle oscillator in any patch, it will be available to load — a brilliant touch.

The Iridium Keyboard is an octave shorter than the Quantum and weighs 4kg less, but is still an impressive‑looking instrument.The Iridium Keyboard is an octave shorter than the Quantum and weighs 4kg less, but is still an impressive‑looking instrument.


The Iridium offers no fewer than three multi‑mode filters. These are arranged as two filters and a ‘Digi Former’. This arrangement is a hangover from the Quantum, where the flexible Digi Former filter enhanced the two analogue low‑pass filters. In the Iridium, the filters combine new and old digital models based on some of Waldorf’s past and present products: SVF, Raiser, Largo, Nave, PPG and Quantum. Each model contains a selection of up to 18 modes that cover the usual low‑, band‑, and high‑pass options as well saturated and ‘dirty’ versions for added grit. The two filters can be linked in various ways to assist with the modulation of frequency and resonance.

The third filter, aka Digi Former, can also operate in other modes such as overdrive, comb filtering, bit crushing, and ring modulation. It can be placed before, after, or in parallel with the dual filters. Any oscillator can bypass the filters or send a varying mix to the dual filters and the Digi Former. In short, filter routing is highly flexible, and a dedicated routing page with graphics shows the audio signal flow update in real time as changes happen.

One significant improvement from the Quantum is that the digital filters are true stereo, making the entire signal path stereo. In the Quantum, using the analogue filters would mix the stereo oscillators down to a single channel — a compromise that Gordon Reid noted in his list of cons in his original review.


No good synth is complete without modulation possibilities, and the Iridium certainly delivers. There are six LFOs per layer comprising the usual waveforms. Speed varies from 240 seconds/cycle to 100Hz, and all waveforms can be wave‑shaped. Each has attack and decay to fade the modulation in and out; per voice, global or single triggering; phase and delay.

There are also six envelopes: amp, two filter envelopes and three free envelopes, although they can all be assigned freely in the modulation matrix. Each envelope is DADSR with variable attack, decay and release curves plus two types of looping.

Finally, there’s the Komplex modulator — two multi‑stage waveforms, which you can blend between, warp, slew and jitter. The Komplex lives up to its name, producing a complex, looping, potentially ever‑evolving modulation source, all sync’ed to MIDI tempo if that’s your bag.

Modulation is handled by a 40‑slot modulation matrix, which should be enough for anyone. There are shortcuts for many common modulation routings, with some, like filter envelope amount or amp velocity, having dedicated front‑panel controls.