4ms Spectral Multiband Resonator (2015–)

A ring of colored lights pulses, each one a frequency waiting to be struck, bent, or set spinning.

Overview

The 4ms Spectral Multiband Resonator (SMR) is not a passive EQ clone. It's a resonant filter bank for a modular system, and it does a lot more than filter. It thinks in scales, responds to triggers, and turns white noise into marimbas. Power it on and a ring of 20 full-color LEDs lights up. The sliders move like a graphic EQ, but twist the Rotate knob and the frequencies start to orbit. Spread them wider, morph between positions, lock individual bands in place. The module responds to control voltage and almost improvises with it.

At its core, the SMR is a six-channel resonant band-pass filter bank. Each of the six bands can be assigned a frequency from a 20-note scale. The scales aren't just Western temperaments. They cover Indian ragas, just intonation, microtonal experiments, and user-defined tunings where every note can be tuned to the cent. You can rotate the whole chord structure up or down the scale via CV or trigger, so you can generate evolving harmonic sequences without a sequencer. Feed it a clock and the bands spin like a music box unwinding. Feed it an audio signal and it can extract spectral envelopes, vocode in real time, or isolate and amplify specific frequency events.

Turn up the resonance, hit the input with a trigger, and the filters ring out like struck metal bars - bright, metallic, and decaying in a way that sounds almost acoustic. It's not a sample and not a simulation. It's the resonance of the filter circuit itself being excited. Musicians who've used it in live sets report that audiences lean in when it's active, drawn to the sound and to the light show that mirrors every frequency shift. The SMR is also dense. There's a learning curve, not because it's poorly designed, but because it has a lot of interlocking systems. The manual is essential, not optional. Once you've worked out the relationship between Rotation, Spread, Morph, and Lock, it starts to feel intuitive.

Specifications

Key Features

The Light Ring as Interface

The ring of 20 multicolor LEDs is the center of the SMR's interface. Each LED corresponds to a frequency step in the current scale, and the active filters light up in real time as they rotate, spread, or jump between positions. You can see the chord structure unfold, the intervals widen or compress. You can also customize the color scheme, from monochrome whites to full rainbows, and save your palette to memory. When you're tweaking Spread with one hand while clocking Rotation with the other, the lights work as a guide. In a dark studio, they look like a bioluminescent creature pulsing in response to sound.

Rotation, Spread, and Morph: The Motion Engine

Rotation shifts all six filter frequencies up or down the scale in unison, like turning a dial on a harmonic wheel. Send a trigger to the Rotate Clockwise input and each band steps up one note. Do it again and they step again, which is good for generating arpeggiated chords from static drones. Spread controls the interval between adjacent bands. At minimum they cluster tightly. At maximum they stretch across the scale, creating wide, dissonant harmonies. Morph is a crossfade between frequency states. When you change Rotation or Spread, Morph determines how fast the filters glide to their new positions. Set it slow and you get smooth, evolving timbral shifts. Set it fast and it snaps, which suits rhythmic modulation. Patch a clock into Morph CV and the whole filter bank breathes in time, swelling and contracting.

Spectral CV and Vocoder Mode

Each of the six filter bands outputs an envelope follower signal (Env Out), which tracks the amplitude of its frequency band. Route those CVs to control the levels of another sound source, say a bank of oscillators, and the SMR becomes a six-band vocoder. It extracts the spectral shape of your input and imposes it onto whatever you feed with the CVs. It's not as polished as a classic 10-band vocoder, but it's raw, immediate, and deeply musical. The Env Outs can also act as trigger sources, spitting out gates whenever a frequency band is excited. That works for rhythm extraction from field recordings or live audio. Pair it with a drum module and your voice or a passing car becomes a beat generator.

Historical Context

The SMR emerged in 2015, as Eurorack was moving beyond boutique circles and into mainstream electronic music. Most filter modules at the time were either analog throwbacks (ladder filters, state variables) or digital novelties with fixed behaviors. The SMR wasn't trying to emulate anything. It was inspired by Buchla's filter banks and Serge's audio integrators, but built with modern microcontrollers and RGB LEDs, so it bridged experimental West Coast synthesis and contemporary digital control. It arrived alongside Mutable Instruments' Clouds and MakeNoise's Morphagene. Those focused on texture and memory, while the SMR focused on harmonic motion and real-time interaction.

Its closest ancestor might be the Buchla 292C Low Pass Gate / Resonant Bandpass Filter, which also used multiple resonant filters for spectral manipulation. The SMR goes much further, with programmable scales, CV control over every parameter, and a user interface that feels more like a digital instrument than an analog module. It arrived when modular users wanted tools that could transform, analyze, and interact with sound, not only generate tones. It kept the tactile, patchable ethos of Eurorack. It was an open system, fully documented, with firmware updates that added features over time (like the v5.1.1 bug fix in 2020). That long-term support made it a favorite among serious builders and performers.

Collectibility & Value

The SMR has held its value well since its 2015 debut. New units still list for $475, and used ones typically sell between $400 and $450 depending on condition. It has gained in reputation and become something of a "must-have" for advanced Eurorack systems. It's not a beginner module, and its complexity keeps casual buyers away, so the people who own it tend to keep it. There are no widespread reliability issues. The build quality is solid, with sturdy knobs, reliable jacks, and a well-designed PCB. The only real point of failure is the power jumper, which allows users to reroute the +5V supply to +12V for higher current draw. If it's set incorrectly it could cause instability, but that's user error, not a design flaw.

When buying used, check that all 20 LEDs function and that the sliders move smoothly without crackling. The firmware should be up to date (v5.1.1 or later), and the module should recall saved banks properly on startup. Some early units had issues with the Scale Rotation switch, but those were addressed in later production runs. The included power cable and screws are standard, so missing accessories aren't a dealbreaker. Because the SMR is firmware-upgradable, confirm that the unit can still accept updates. No new features have been added recently, though the possibility remains. A mint-condition SMR with original packaging and documentation might fetch $500, but that's more about completeness than performance.

Market Value

┌──────────────────────────────────────────────────────────────────────────┐
│ 4MS MULTIBAND RESONATOR                                         Nov 2026 │
├──────────────────────────────────────────────────────────────────────────┤
│ High      $420                                    Latest            $420 │
│ Median    $334                                    Trend                — │
│ Low       $297                                    Volume           ~2/mo │
├──────────────────────────────────────────────────────────────────────────┤
│   $500 ┤                                                                 │
│        │                                                                 │
│        │                                                                .│
│   $371 ┤                                                                 │
│        │                       .                                         │
│        │.                          .                                     │
│        │                                                                 │
│   $200 ┤                                                                 │
│        ├─────────────────────────────────────────────────────────────────│
│    vol │█                      █   █                                    █│
│        └─────────────────────────────────────────────────────────────────│
│         2026-05                      2026-06                      2026-07│
└──────────────────────────────────────────────────────────────────────────┘

eBay Listings

Recently sold on eBay: $297–$420 (median $334, based on 4 completed sales, past 12 months)

4MS SPECTRAL MULTIBAND RESONATOR (SMR) : NEW : [DETROIT MODU

$475

4MS Spectral Multiband Resonator SMR EURORACK - NEW - PERFEC

$475

4MS Spectral Multiband Resonator SMR EURORACK

$320

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