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Mutable Instruments Shelves Eq Filter


EQ filter



Shelves brings to Eurorack modular systems something we are all very familiar with: the 4-band parametric EQ typically found in console channel strips. But this time, there’s CV control! The first band is a low-pass shelving filter, the fourth band a high-pass shelving filter, and band #2 and #3 have full-blown parametric controls with bandwidth (Q) adjustment. All analog.

Shelves will provide a subtler spectral shaping & coloring than standard multimode filters. It is particularly useful in the feedback loop of effects or more generally in feedback patches in which the slightest tonal change has drastic consequences. Or as a novel way of shaping sounds obtained by west-coast techniques. Or as a formant-ish filter. Or to emulate the body of instruments in the context of physical modelling patches…

Unlike console EQs, each band is not restricted to a narrow range of frequencies: it can be swept across the entire audio range, from 20 Hz to 20kHz – with unexpected phase cancellations or reinforcements when corrections compete in the same frequency range. All parameters have direct CV control. Global frequency and cut/boost CV inputs allow simultaneous CV control of all channels.


Shelves’ two parametric sections are, behind the scenes, full-blown 12-dB multimode filters. The expander panel gives you access to their low-pass, band-pass, and high-pass outputs.

New! Modules made after september 2015 combine the main module and the expander panel into a single 18-HP module.


Shelves demos


Coming soon…




Voltage controlled EQ with sweepable low-shelf, high-shelf, and two parametric sections.


  • Scales: all frequency CV inputs: 1V/Oct. All cut/boost CV inputs: 3dB/V.
  • Low-shelf frequency and cut/boost CV.
  • High-shelf frequency and cut/boost CV.
  • Parametric 1&2 frequency, cut/boost and Q CV.
  • Global frequency offset and cut/boost CV.
  • Signal input.
  • Signal output.


  • Low-shelf/Parametric/High-shelf correction frequency, 20 Hz to 20kHz.
  • Low-shelf/Parametric/High-shelf cut/boost, -15dB to 15dB.
  • Parametric correction Q, 0.5 to 20 (up to 1000 with external CV offset).


The parametric sections are realized with state-variable filters, whose high-pass, band-pass, and low-pass outputs are available on a header on the back of the module or through an expander.

Modules made after september 2015 include these individual outputs at the right of the panel.

Technical characteristics

  • Analog signal path.
  • All inputs DC-coupled.
  • Input impedance 100k (25k for the global frequency and gain CV inputs).
  • Open-source hardware.
  • 18-HP (16-HP for modules made before september 2015 and which do not include the individual filter outputs).
  • Current consumption: +12V: 75mA ; -12V: 75mA.

Shelves user manual


Mutable Instruments’ Shelves is a voltage-controlled signal processor inspired by the EQ section of console channel strips. Just like many sought-after equalizers, it provides low-shelf, high-shelf, and two parametric tone controls. Unlike an equalizer, each of these four tone controllers can be swept over the entire audio range; and their parameters can be freely modulated with control voltages.

Shelves occupies a space between tone-controllers and filters, sometimes achieving sounds reminiscent of a filter bank. It provides a subtler and less cliché’d way of spectrally altering complex drones or feedback patches.

Download the quick start guide.


Mutable Instruments’ Shelves is designed for Eurorack synthesizer systems and occupies 16 HP of space. It requires a -12V / +12V supply (2×5 connector), consuming 75mA from the -12V rail and 75mA from the +12V rail. The red stripe of the ribbon cable must be oriented on the same side as the “Red stripe” marking on the printed circuit board.

Parameter ranges

On all channels, the FREQ knob covers the entire audio range, from 20 Hz to 20kHz. This is radically different from a classic EQ, in which each section operates in its narrow frequency range. Strange things (positive/negative interferences or phase effects) can happen when two sections overlap.

All the FREQ CV inputs have a 1V/Oct scale and act as offsets to the value set by the FREQ knobs.

On all channels, the GAIN knob covers an attenuation/boost range of -15dB to +15dB. The GAIN CV input has a 3dB/V scale and acts as an offset to the value set by the GAIN knob. Gains above +15dB cannot be reached, even by adding a positive CV offset to the GAIN CV input. However, gains below -15dB can be obtained by adding a negative CV offset to this CV input.

On parametric channels, Q goes from 0.5 to 20.0 from the panel knob, but can reach higher values, up to 1000.0 through external CV modulation.

Controls, inputs and outputs

A. High-shelf section. This section boosts or attenuates all frequencies above the FREQ control. TheGAIN potentiometer controls the amount of attenuation or boosting. No modification is applied whenGAIN is in its central position.

B. Parametric sections 1&2. These two sections boost or attenuate all frequencies in a frequency band whose central frequency is set by FREQ. The narrowness of this frequency band is set by theQ setting – from very wide to very selective.

C. Low-shelf section. This section boosts or attenuates all frequencies below the FREQ control. TheGAIN potentiometer controls the amount of attenuation or boosting. No modification is applied whenGAIN is in its central position.

1. 2. Global frequency and gain CV inputs. These CV inputs simultaneously adjust the FREQ orGAIN of all 4 channels.

3. IN. Audio input. The input signa

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