Waldorf Iridium Desktop MK2 review - Extreme synthesis density

The Iridium series was launched in 2020, based on the Quantum, the flagship of the lineup, and incorporates most of that unit’s capabilities—except for the analog filters. The Iridium synths are advanced digital synthesizers (available in keyboard, module, and compact module formats) that provide various forms of synthesis combinable within three oscillators, which are then processed by a variety of extremely flexible multimode filters, modulated in real time via numerous modules, and enhanced by a robust effects section.

Following the Quantum, it’s now the Iridium series’ turn to upgrade to MK2. The update includes a boosted CPU board, providing 6 GB of flash memory for samples as well as increased processing power, enabling a new synthesis engine, expanding multitimbrality to four channels, and adding new features here and there. Let’s take a closer look at all of this on an Iridium MK2 kindly loaned by the German manufacturer (firmware version 4.0.6)…

Construction and ergonomics of the Iridium MK2

The MK2 is as well-built as its predecessor. It features a medium-gray metal chassis, a responsive color touchscreen, knobs with aluminum caps and securely mounted metal shafts, precise click-stop push-button encoders, and screw-lock connectors.

The module is a comfortable size, measuring 44 × 31 × 9 cm (17.3 × 12.2 × 3.5 inches) and weighing 4.8 kg (10.6 lbs.). The lower section houses the direct controls for the main parameters: oscillators, mixer, filters, digital processor, envelopes, and LFOs. Given the plethora of available parameters, you often need to access the menu to edit settings. This is done in the upper section using the touchscreen, the eight module selection buttons, and the six context-sensitive encoders.

The graphics are both attractive and precise, perfect for keeping track of everything that’s happening. The ergonomics are very well thought out: display of stored/edited values, different resolution levels, MIDI CC assignment via learning… however, there’s no “compare” feature. Too bad; it would be a time-saver.

A section to the right of the screen lets you select the playback mode, load/save a program or layer, or launch an arpeggio or sequence. Finally, on the right, the 16-pad multicolored array lets you play notes, chords, arpeggios, and sequences. These are simple switches, which isn’t great in this price range.

The connectors are screwed or crimped to the rear panel. They include a DIN terminal for an external power supply (via a central power supply unit), a 6.35 mm (1/4-inch) headphone output with mini-pot volume control, stereo audio outputs and inputs on 6.35 mm (1/4-inch) TS jacks, for sampling a signal or processing it via the granular engine, filters, or effects.

In addition, you’ll find eight mini-jack connectors: four CV inputs, one Gate input, one Start input for the arpeggiator or sequencer, one clock input and one clock output.

There’s a MIDI DIN trio, a USB-B port to computer (MIDI 2.0 / MPE, CC, NRPN, and SysEx), a USB-A port to a controller or storage device, and a microSD card slot (for managing programs, samples, oscillators, wavetables, MIDI tables, system). It’s truly a shame that there’s only one pair of stereo outputs given the instrument’s multitimbral capabilities, and that USB audio wasn’t included.

A very user-friendly and high-quality sound library, with over 2,000 preloaded programs

After 20 seconds of initialization, the Iridium MK2 provides access to several thousand programs, including approximately 2,000 that come preloaded. They were developed by leading figures in sound design (including Kurt Ader, Richard Devine, Joerg Huettner, Matt Johnson, Howard Scarr… not to mention our friend CO5MA).

Sounds can be selected by number, bank, author, type, and four customizable attributes, which can be saved when saving programs. For immediate efficiency, you can organize your preferred programs into favorites (12 tabs of 20 sounds each). A function allows you to load an entire program or one of its four sound layers.

The knobs can respond in step, threshold, or relative modes. We appreciate their precision and the three resolution levels offered for each continuous parameter. The front-panel controls transmit MIDI CCs and are easily assignable to a modulation source—we’ll come back to that. This also works in the menus. Holding down the desired parameter opens a dialog box for its assignment.

The Iridium MK2’s sound quality is excellent: high output levels with no background noise, wide bandwidth, and beautiful stereo depth. The sounds are crystal-clear, finely detailed and precise. We appreciated the PPG-style evolving textures, the atmospheric chorus sets, the dreamy ambiences, the various modeled percussion sounds, the ethereal wind instruments, and special effects of all kinds.

A new engine, dubbed “Seeds, ” has made its debut. It adds highly evolving wavetable-style sounds, but with a potentially different synthesis method at each stage. That allows for a sequence of distinct sonic colors as the table unfolds, which enriches the synth’s palette (the first five sound samples use this engine). It’s particularly well-suited for ambient music and sound design. It also produces some VA-style polyphonic sounds, but the Iridium lacks the thickness and natural fluctuations of polyphonic analog synths, as well as the punch of a monophonic synth. On the other hand, it blends very well with dense sounds, adding edge or subtle fluctuations.

Iridium Dekstop MK2_1audio 01 Arped Seeds

00:0001:06

Link

Code

• Iridium Dekstop MK2_1audio 01 Arped Seeds01:06
• Iridium Dekstop MK2_1audio 02 Evol Seeds00:44
• Iridium Dekstop MK2_1audio 03 Particle Seeds01:16
• Iridium Dekstop MK2_1audio 04 Stacked Seeds00:41
• Iridium Dekstop MK2_1audio 05 Rezbell Seeds00:47
• Iridium Dekstop MK2_1audio 06 Running Man00:32
• Iridium Dekstop MK2_1audio 07 Polymoog Mod00:48
• Iridium Dekstop MK2_1audio 08 Poly Arp00:57
• Iridium Dekstop MK2_1audio 09 Layered Seq00:55
• Iridium Dekstop MK2_1audio 10 Multi Arp01:26

 ALL_WAV

Programs with four layers of sound arranged in different modes

The Iridium Desktop MK2 is a 16-voice polyphonic, 4-channel multitimbral digital synthesizer (two more channels than the first-generation Iridium). Each program features four sound layers that can be played individually, across different ranges (split with overlap options, separate but unfortunately global MIDI channels), stacked across the entire keyboard, or in rotation (cyclic or random).

These latter modes are derived from the company’s Protein module. For each layer, you can adjust the volume, pan, velocity-sensitive volume, audio input gain, audio input routing (to the output, filters, or the layer’s effects), and unison mode (number of voices, detuning, stereo width, delay). Only one layer can be edited at a time, as the software selection buttons 1–2–3–4 are mutually exclusive.

In Split mode, you can set the voice reserve per layer. In Stack mode, polyphony is divided according to the number of active layers, as you’d expect. A new Mutator page lets you randomize certain synthesis and effects parameters—well beyond just pitch—either globally or individually, with the result adjustable via the encoders.

Each voice features three oscillators, two parallel filters, a signal processor, and an amplifier. In addition, there’s a complex modulation generator, six envelopes, six LFOs, and a modulation matrix. Each oscillator offers a choice of six synthesis engines: Wavetable, Waveform, Particle Generator, Resonator, Kernel Synthesis, and Seeds.

On the front panel, you can adjust the key parameters of the selected engine (see below) and the oscillator’s pitch (octave/semitone, hundredth). However, you must access the menu to adjust keyboard tracking for pitch (bipolar), volume (normal, fine, or superfine precision), panning (same), the oscillator’s destination (dual filter, signal processor, amp, with filter balance in 5% increments), the volume of ring modulations (1×2 and 2×3), the amount of pitch bend, and pitch variation (a simulation of analog oscillator fluctuations). The other parameters depend on the synthesis engine. At the global level, you can choose a tuning system from a long list of presets or program up to eight user-defined tunings—great for fans of microtonal scales.

First engine: Wavetable

The first oscillator type is Wavetable, a Waldorf specialty since the beginning, carrying on the PPG legacy. This form of synthesis involves playing back a sequence of short waveforms—with more or less smooth transitions—by modulating the playback position using various sources to create rich spectral variations.

This allows you to play perfectly synchronized chords or completely uncorrelated notes, depending on the modulation sources chosen. Direct controls let you adjust the transposition of the sound spectrum, the noise level, the initial playback point in the table, saturation, and cyclic playback modulation. It’s actually surprising that you can’t change the wavetable directly on the front panel; Waldorf didn’t prioritize upgrading the MK2 with dual concentric encoders like on the company’s M module.

You use the menu to select a Wavetable from among the 84 preloaded tables (ranging from 14 to 380 waves) and all the ones you’re sure to create yourself. Next, you set the initial playback position in the table, the initial phase, the spectral content (transposition of the harmonic content), the brilliance, the keyboard tracking assigned to the spectral content, the table cycling mode (per-voice cycle, global cycle, tempo sync, single play, per-voice ping-pong, global ping-pong), the quality (clean, harsh, or dirty, to simulate the aliasing of vintage PPG and Waldorf synths), the type of interpolation between waves (with or without fade), sweep smoothing (smooth or grainy), saturation (drive, gain), and the speed of cyclic playback through the table (positive or negative).

The screen displays a 3D representation of the Wavetable’s spectrum, which you can explore by changing the starting position—it’s magnificent! The synth also offers a toolkit for creating and exporting wavetables. For example, resynthesize a phrase played on the keyboard, analyze an imported audio file, or create a table of eight short waves from a WAV/AIFF file, with a maximum of 1,024 samples (recalculated as needed), or convert a WAV/AIFF file into a constant-period wavetable (between 64 and 4096 samples). Tables can be imported/exported via the micro-SD card reader. Kudos for this built-in editor!

Second engine: Waveform (analog modeling)

This oscillator can stack up to eight waveforms without losing polyphony. On the front panel, you can set the number of stacked waves (decimal values represent intermediate levels), their detuning, the base waveform (sawtooth, sine, triangle, variable pulse, pink noise, or white noise), the harmonic content, and the amount of synchronization with a virtual master oscillator (which avoids using another sound generator).

The harmonic content varies depending on the waveform. With the sawtooth, you gradually transition from a double sawtooth to a single sawtooth, then to a square wave. With the sine wave, it transitions from a gently sloping ramp to a sine wave, then to a smoothed sawtooth.

The triangle wave transitions from a ramp to a triangle wave, then to a sawtooth wave. If you choose the pulse wave, you can adjust the pulse width from nearly zero to almost 100%. Finally, with the two noise types, we transition from filtered noise to unfiltered noise, then to variable-pitch noise.

As always, the central editor is very polished and displays the resulting waveform in real time as you shape it, which is very educational. Through the menu, you can access additional parameters: stereo width of the stacked waves, detuning by semitone and by wave pair (1–5, 2–6, 3–7, 4–8) and oscillator phase (free oscillation or forced phase start on each note trigger).

You can also load, name, and save preset waves, just like with the wavetables. This is a highly sophisticated engine that, once again, doesn’t merely imitate the existing sounds.

Third engine: Particle Generator (granular synthesis)

The third type of oscillator, called the Particle Generator, involves manipulating samples, multisamples, or audio streams. It can operate in classic sample playback mode, granular resynthesis, or live granular synthesis (direct processing of an external signal).

Samples come from internal memory, a micro-SD card, recordings made directly from the device, or the audio input. Samples can be edited just as in Global mode (see box). You can also assemble them into multisamples, to play them back simply or resynthesize them via granular mode. Options include sample selection, pitch, range and velocity window.

If you assign the same range and velocity to multiple samples, you can then alternate between them according to different rules: ascending order, descending order, ping-pong, random—the competition would do well to take a cue from this!

In granular mode, samples, multisamples, or audio streams are split into grain streams. From the front panel, you can adjust the number of grain streams (1 to 8), the detuning of the streams, the sample’s playback start point, the grain length (up to 250 ms), and the playback oscillation direction (forward or backward).

Via the menu, in granular mode, you can access additional parameters: random start point, gate (grain density), agitation (random variation in grain length and density), playback mode (continuous, single shot, ping-pong, global—all of which can be adjusted in real time without having to retrigger the sound), envelope attack, envelope decay, and stereo width.

You can also adjust the pitch of the grains: dispersion relative to the central pitch, dispersion mode (various rules, some of which are random or set by semitones…). Here again, you can load and save presets, and the display is very intuitive, helping you understand what you’re doing and how it affects the samples. A successful and unique synthesis engine.

Fourth engine: Resonator (physical modeling)

The fourth type of oscillator, the Resonator, combines an excitation source (short noise, sample, or multisample) with a resonant body (a bank of bandpass filters). On the front panel, you can directly adjust the number of repetitions of the excitation, the spacing between partials, the timbre (filtering or accentuation of partials), the nature of the excitation (from a pulse to simulate a strike to a short noise to simulate a breath), and the resonance of the partials (duration).

The screen displays the resulting spectrum in real time as a harmonic series. Through the menu, you can adjust the amount of accentuated partials (shifting from a woody sound to a metallic one), the brilliance (ratio between low and high harmonics), the excitation envelope (AD), the acceleration of repetitions (for example, to simulate a bouncing ball that eventually comes to a stop), the filtering balance of the partials, high-frequency filtering (between the excitation and the filter bank), stereo width, and fundamental boost. As always, there is a bank of loadable and editable presets for creating your own resonators.

Within the resonator-type oscillator, just like in the Particle Generator engine, you can edit samples and assemble them into multisamples, which can then be used as an excitation signal. The only difference here is that there is only one alternation mode for samples with the same pitch range and velocity window.

The sounds produced with this type of oscillator range from wooden percussion to metallic percussion, wind instruments, and trickling sounds. It’s an oscillator just waiting to be explored, capable of producing unusual sounds—sometimes organic, sometimes acoustic.

Fifth engine: Kernel Synthesis (algorithmic synthesis)

Next up is the fifth type of oscillator, based on an arrangement of six mini-oscillators or operators that Waldorf has named “Kernels.” These can be combined and cross-modulated in the audio signal and edited in two different modes.

The first, Template, is for quick adjustments using the five front-panel knobs in the oscillator section, which become context-sensitive based on the selected template. The screen displays a page with the assigned parameters, which you can then modify to save your own templates. This allows you to use this mode without getting too lost in the details.
The second mode, aptly called “Edit, " allows you to delve into the infinitely small. You can arrange the six Kernels into algorithms (DX7-style), with three modulation sources per Kernel (a Kernel can be modulated by one to three others in the audio signal).

There are several types of modulation: phase (DX7), linear FM, ring modulation, AM, and wavetable playhead position. For phase and amplitude modulation, you can set a feedback level for each Kernel. The screen displays the algorithm as it is being formed in real time, showing all the routings and modulations created.

You can also assign the five front-panel knobs to six simultaneous parameters per knob (a modulation matrix-style macro system where each cable selects the parameter and the amount of bipolar modulation). Editing at the Kernel level is done via dual tabs, allowing you to easily switch between Kernels within a given parameter page (waveform, modulations, envelope, and level). On the Waveform page, you select the waveform type: sine, ramp, sawtooth, square, white noise, pink noise, resonator, or internal wavetable. You can set the initial playback point of a wavetable, its phase, and its level (volume and/or modulation, depending on whether the Kernel is a source and/or a modulation) and its pitch type (constant ratio, allowing you to obtain harmonics or partials, or fixed frequency).

On the Modulation page, you define the routings of the three modulation-source Kernels for the current one. On the Envelope page, you adjust the level envelope (volume and/or modulation) of the Kernel, which is of the AD1D2 type with keyboard tracking. Finally, on the Level page, you control the level, velocity response, keyboard tracking, and panning. Once again, this is a full-fledged synthesis engine that also allows you to import banks of 32 DX7 programs via Sysex. Isn’t life beautiful?

Sixth engine: Seeds (multi-synthesis tables)

Finally, the Iridium Desktop MK2 introduces a sixth, entirely new type of oscillator, called Seeds, which the previous Iridium and Quantum series do not have (and apparently will not have) due to computational power limitations.

The sound structure is based on wavetables, which can contain up to 12 Vectors (stages). The difference from a classic wavetable oscillator is that here, rather than chaining together static wavetables, Seeds are used—variable oscillators generated from different types of synthesis: four-part additive synthesis, wavetables, FM with feedback, ring modulation, and a complex noise generator (wind, rain, interference, crackling…).

Each Seed can stack up to four virtual oscillators (of the same synthesis type), producing an effect similar to a chorus (detuning + stereo spread). A dedicated envelope (free-form) allows you to directly modulate the Seed’s evolution. The vector table (or Seed table) is scanned in the traditional manner, starting from a programmable initial point.
All of this can be edited in a cascading manner, starting with global settings on a multicolored 3D graphical interface that’s even more beautiful than that of the Wavetable oscillator (you can see the waveforms change in 3D as you add vectors, modify the Seed type, or add virtual oscillators).

The other pages allow you to edit the 1 to 12 vectors via a drop-down list, with options to select the synthesis type, volume, transposition, and parameters specific to each synthesis type. All settings are highly customizable via the matrix.

For those who might feel overwhelmed, the designers have included presets with useful settings and a random generator (“Lucky”) that can operate using five more or less outlandish calculation modes. The more adventurous, meanwhile, will relish the fact that everything is programmable from A to Z. We truly appreciate that the developers have gone to great lengths to enhance a synth that’s already very comprehensive in terms of its oscillator engines.

Two digital resonant multimode filters combined in parallel

The filter section of the MK2 is similar to that of the first series, namely two stereo resonant multimode digital filters in parallel. Their respective cutoff frequencies and resonances can be linked or independent, depending on their configuration: Single (only the first filter is active), Boost (second filter non-resonant, lower frequency linked to that of the first), Twin Peaks (constant distance between the cutoff frequencies and resonances of the two filters), Escaping (frequency separation increasing with the frequency of the first filter), Opposition (the second filter’s frequency changes in opposition to that of the first), Endless (Twin Peaks followed by Opposition when the second filter’s fixed frequency reaches its maximum), Independent (separate settings for both frequencies and both resonances), Linked (as above, except that the first frequency controls the second).

Each filter offers six models available in different modes: state variables&(LP/BP/HP x 2/4 poles x 3 input levels: classic/saturated/dirty = 18 modes), slope varying with resonance (LP/HP x 2/4 poles x 3 levels = 12 modes), Largo (18 modes), Nave (18 modes), PPG Wave 3.V (LP x 2/4 poles x 3 levels = 6 modes), and Quantum (six modes).

Filters of any type can enter self-oscillation. All continuous controls offer, once again, three resolution modes: normal, fine, and superfine. On the front panel, you can directly adjust the cutoff frequency, resonance, and filter type for each filter, as well as their interconnection.

There is no step effect on the cutoff frequencies; the resolution is in the order of one-thousandth. Via the menu, you can adjust the response of the keyboard, envelope, or velocity to the frequency, as well as the volume and pan of each filter. The screen displays the filters’ response curves in real time very smoothly, and you can edit them using drag-and-drop; it also lets you visualize the routing of the various sound components—oscillators, filters, signal processor, amp, effects… very educational!

A signal processor that can be combined with the two digital filters

The audio processing section doesn’t stop there, as it also includes a signal processor. It can be placed before, after, or in parallel with the two filters. Highly versatile, it is capable of producing various drive effects, bit crushers, and sophisticated digital filters.

On the front panel, you can select the effect type and adjust two parameters related to the chosen mode; the rest is configured via the menu. For the drive effects, you can select from different circuit models: transistor, tube, electret microphone, diode, Crunch (an FM-based waveshaper), and Cuff (distortion similar to the Big Muff-style distortion, we believe). There’s also a gain algorithm with reversible phase.

Next are two comb filters (positive and negative), for which you can adjust the frequency and feedback. For the Bit Crusher, you can adjust the resolution and sample rate in real time.
The filter algorithms offer access to various models derived from various Waldorf synthesizers. First, the Nave and Largo in low-pass, band-pass, high-pass, and 2– or 4-pole notch modes. Next, the PPG Wave 3.V in 2– and 4-pole low-pass modes. Finally, there are three types of stereo formant filters, allowing you to simulate different vowels with the option to offset the formants between the left and right audio channels.

Regardless of the filter mode, you can adjust the cutoff frequency and resonance on the front panel; through the menu, you can access additional parameters, such as the routing of the oscillators and the various filters. The sound quality of this signal processor is varied and rich, making it an excellent complement to the two digital filters.

Modulations, Part 1: LFOs, Envelopes, and the Flavour Parameter

Waldorf has specialized in modulation matrices since the very first Microwave in 1989. The Iridium Desktop MK2 continues this tradition of excellence. The Glide features a trigger mode (continuous or between tied notes) and a time control, which can be modulated via the modulation matrix, allowing for the generation of complex portamento effects.

Next are six identical LFOs, which share just two controls on the front panel: frequency (from four minutes to 100 Hz) and depth. The numerous additional settings are accessed via the menu: waveform (sine, square, triangle, sawtooth, ramp, S&H), clock synchronization, continuous wave distortion (compression for sine, morphing for triangle, pulse widthpulse width for square, folding for sawtooth waves, edge distortion for S&H), fade-in, fade-out, synchronization between voices, wave smoothing, phase, delay, polarity (single or double), and direct targets.
Next come six envelopes, which share the ADSR controls on the front panel in pairs, as well as the velocity response and modulation amount (shared by all six envelopes, except for the amp envelope, which has its own modulation amount control). The first three are pre-assigned to the two filters and the amp, but they can be rerouted via the matrix.

The menu allows you to edit all parameters across six tabs (as with the LFOs) : DADSR segments, phase shift of the AD segments (to simulate a vintage analog synth), ADR curve shapes, looping (AD or ADSR), retriggering (single, multiple), and direct targets. Here again, the screen displays the envelope curve in real time; you can drag it, and you can see each voice follow it—it’s both fun and educational! Durations range from 0 to 60 seconds, which is very convenient.

The MK2 includes the Flavour parameter, which first appeared on the Protein. It’s a comprehensive module that generates calculated (or pseudo-random) micro-variations between modules, each with its own intensity settings: three oscillators, two filters, envelopes, pitch, volume, and pan. A front-panel knob lets you control the overall effect. This animates the sound in interesting ways, creating subtle differences between the voices.

Modulations, Part 2: Komplex Modulator and Note Locks

We continue our journey through the wonderful world of modulation with the Komplex Modulator (in Goethe’s language), a superb LFO with two simultaneous waveforms, ideal for pads and drones. You can adjust the frequency, the blend of the two waves, their modulations, and the entropy (random modulation with each cycle); the screen displays the resulting modulation curve. You can then edit it in 32 steps: level and transition curve to the next step (linear, discrete jump, cosine, sawtooth). Numerous additional settings are available, identical to those for the LFOs.
The Iridium Desktop MK2 introduces a new module called Note Locks, which was developed in collaboration with Aphex Twin. It allows you to assign 16 parameter variations to each of the keyboard’s 128 notes. This applies to virtually all synthesis and effects parameters, including the type of synthesis engine.

From an ergonomic standpoint, it’s very simple: in the editor, you enable recording, play a note, adjust up to 16 parameters, stop recording, and then move on to the next note. Copy, paste, and delete functions are available to simplify the process. Very original! According to our information, it seems unlikely that the older Iridium/Quantum series will be equipped with this feature, given the processing power required.

A powerful modulation matrix that can control almost anything

Finally, there is a 40-cable modulation matrix to connect 56 sources to 207 destinations, if we’ve counted everything correctly. For each cable, you select the source, the destination, the modulation amount (bipolar), the modulation controller, and the amount of control from that controller.

The front-panel controls make it easy to assign a destination to a source represented there (envelope, LFO). Most of the time, however, you’ll need to go through the menu to access all available parameters. This is quick and easy: the matrix page displays a drop-down list of cables and the modulation amounts as red or green horizontal bars, depending on the sign. You select the connection to edit using an encoder and access all parameters via the other context-sensitive encoders. You can edit or delete a string at any time.
Among the available sources: LFOs, envelopes, the complex modulator, voice number, a random generator, external physical controllers (including polyphonic pressure and the MPE Y-axis), several MIDI CCs, a random generator, a virtual X/Y pad on the screen, the eight modulation lines of the parameter sequencer, and the four CV inputs.

Destinations include: overall pitch or per oscillator, the level of each oscillator, oscillator parameters (almost all), filters and the signal processor (all parameters, including levels and panning), volume, panning, segments of each envelope, the speed and gain of each LFO, the complex modulator parameters, the glide time, certain effects parameters, and certain parameters of the arpeggiator and sequencer. Kolossal!

We appreciated the ability to modulate the wavetable number—a rare feature, especially since the result is very well controlled, with no unwanted side effects.

Modulable multi-effects available for each sound layer

A program featuring four sound layers; Waldorf had the brilliant idea of equipping each one with a separate chain of five multi-effects (mostly stereo), with various predefined serial/parallel routing algorithms. Only one instance of each effect type is allowed in the five blocks of the chain (you cannot have two chorus effects for a given layer, for example). Editing is done exclusively via the menu; there are no direct controls on the front panel.

The list of algorithms assignable to each block is extensive: tremolo, phaser (various types, including those from the Nave and the PPG Wave 3.V, ranging from 2 to 16 stages), chorus (two to eight stages), flanger, stereo delay (with tempo sync), reverb (various colors), four-band parametric EQ, saturation (transistor, tube, electrostatic microphone, diode, Crunch, and Cuff modeling), and compressor (very comprehensive, with all desirable parameters except a side-chain input).

There are usually ten editable parameters per effect, most of which are destinations in the modulation matrix—well done! Our favorite effects are the chorus, which is deep and thick, and the reverb, precise and long-decaying. The phaser sounds nice in PPG mode and metallic in Nave mode, as does the flanger. We appreciate the vintage Big Muff pedal model (Ciff)—a great idea worth expanding upon.

The single stereo output prevents you from applying separate processing to each sound layer or from retrieving an unprocessed layer separately—which is a shame. Finally, on the global level, there’s a bass amplifier (simple on/off), which can be useful depending on the sounds. It’s too bad it’s global.

A reboosted arpeggiator and a mono sequencer with movements

Each of a program’s four layers can use either an arpeggiator or a step sequencer (which are mutually exclusive). Let’s start with the arpeggiator. You can hold chords (using the Chord button) and add notes to the held chord (using the Latch button).

In the latter mode, pressing a note that’s already being held removes it from the chord. The available parameters are tempo, time division, swing, the rhythmic pattern (31 types with different accents), the delay before retriggering, the release gate time, the playback direction (up, down, up and down, up and down with repeat, down and up, down and up with repeat, random), the’octave (1 to 4), note sorting (as played, reverse order, ascending or descending by pitch, ascending or descending by velocity, chord), and velocity playback mode (all played notes, first note played, last note played).

The MK2 features a polyphonic mode that adds up to four voices, whose behavior relative to the main arpeggio can be defined using several combinable parameters: follow / omit / offset / transpose—some of which can be combined—which considerably enriches the arpeggios produced with minimal adjustments.

For those who prefer programmed patterns to played arpeggios, the Iridium MK2 offers a 64-step sequencer (still mono). For each step, you can set the note, duration, velocity, and 8 assignable modulation lines via the modulation matrix. Programming can be done directly on the screen by drawing the pattern by hand and then editing it with precision.

You can activate a step, mute it (make it inactive without deleting it), or double its length (the next step is skipped but remains in memory). However, you cannot link two steps, create autobend effects, or use Ratchets. You can also enter notes directly using the 16 pads or an external keyboard. Here again, the instrument allows you to save and load sequence presets.

The playback direction is customizable: forward, backward, ping-pong, alternate, and single play. Similarly, you can specify where the sequence starts when you press a new key: at the beginning, in the middle, or at a random step. Sequences can be transposed directly using the 16 pads or an external keyboard. You can even choose a tuning system and a root note. The other parameters (tempo, time division, swing, etc.) are the same as those for the arpeggiator. Note that arpeggiated or sequenced notes can be transmitted via MIDI/USB, which can be configured in Global mode.