Mutable Instruments Rings B-Stock

  • 260.00€

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Rings brings physical modelling synthesis to your Eurorack system, from a more modular angle than Braids’ models or Elements. Instead of trying to be a complete instrument, Rings focuses on the key ingredient, the resonator, ready to be excited by envelope clicks, trigger pulses, granular noise or any other audio source produced by the rest of your system.

Three families of vibrating structures are simulated by the module, with CV control over their parameters:

  • Strings, membranes and tubes as modelled by Elements’ resonator section (modal synthesis).
  • Strings coupled together and vibrating in sympathy, with controllable intervals between them.
  • Strings with a variable amount of inharmonicity.

Rings can be configured so that each new note is played on its own virtual string, while the previously played note(s) still decay(s). This unique take on polyphony allows the module to play strummed chords.


Rings demos




Modal filter bank and comb-filtered based resonator, for physical modelling synthesis.


  • Three resonator models: modal resonator (as used in Elements), sympathetic strings (stack of comb filters), string with non-linearity/dispersion (comb filter with multimode filter and non-linearities in the loop).
  • Pseudo-polyphony of up to 4 notes. Each new note is played on its own virtual string, while the previously played note(s) still decay.


  • Number of strings/structures (1, 2 or 4).
  • Synthesis model (modal, sympathetic strings, string).
  • Main frequency (quantized in semitones).
  • Structure. With the modal and waveguide models, controls the inharmonicity of the spectrum (which directly impacts the perceived “material”). With the sympathetic strings model, controls the intervals between strings.
  • Brightness. Specifies the brightness and richness of the spectrum.
  • Damping. Controls the damping rate of the sound, from 100ms to 10s.
  • Position. Specifies at which point the structure is excited.

Inputs and outputs

  • Frequency, structure, brightness, damping and position modulation CV inputs with attenuverter (-8V to +8V).
  • “Strum” trigger input to indicate when a new polyphony voice needs to be allocated. Normalized to an edge detector detecting changes on the main V/Oct input, or sharp transients on the audio input. Detection threshold at 0.6V.
  • 1 V/Oct frequency input (-1V to +5V).
  • Resonator audio input, normalized to a filtered pulse/noise burst triggered by the “Strum” input. Modular level, up to 16Vpp.
  • Two audio outputs, splitting the signal into even/odd partials in monophonic operation, or even/odd notes in polyphonic operation.

Technical characteristics

  • Input impedances: 100k.
  • AD/DA: 16-bit, 48kHz.
  • Internal processing: 32-bit floating point.
  • Open-source hardware and firmware.
  • Easy firmware updates through an audio interface.
  • Cortex-M4 ARM processor.
  • 14-HP.
  • Current consumption: +12V: 110mA ; -12V: 5mA.

Rings user manual


Rings is a resonator, the essential ingredient at the core of several physical modelling techniques. It transforms an external, unpitched excitation audio signal (such as a click, a burst of noise, or whatever is captured by a contact microphone) into a full-bodied pitched sound. Rings is the bar, the tube or the bunch of strings you cause to vibrate with an external signal.

Download the quick start guide.


Mutable Instruments’ Rings is designed for Eurorack synthesizer systems and occupies 14 HP of space. It requires a -12V / +12V supply (2×5 pin connector), drawing 5mA from the -12V rail and 120mA 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.

Rings’ basics

Polyphony and synthesis method

How the module operates is governed by two settings controlled by buttons at the top of the module. Once these are set, no hidden mysteries!


The first button selects the polyphony of the module: one, two, or four notes. Enabling four notes polyphony doesn’t mean that four CV input jacks will magically appear on the module, but simply that four notes played in sequence will nicely overlap without cutting each other’s tails. To play chords, you will need to “strum” the module by playing a rapid sequence of notes – something you might have already encountered with Braids’ PLUK model. Note that the module might reduce the number of harmonics in the generated signals to cope with the higher polyphony.

The second button selects the three available types of resonators. They are:

Modal resonator. Modal synthesis works by simulating the phenomena of resonance at play in vibrating structures, that is to say the way a string or plate (for instance) will absorb certain frequencies while it will “ring” at some other frequencies, called the modes. When we pluck a string, strike a drum or blow in a tube, the short burst of energy of the blow/impact contains many frequencies. Some of these fall outside of the modes, and are absorbed. Some of these excite the modes, producing a stable, pitched sound. Each mode corresponds to a harmonic or partial in the spectrum of the sound, and is modelled by a band-pass filter. The Q factor of the filter determine how sustained the oscillations of the corresponding partial are. Various materials or structures are characterized by different relationships between the frequencies of their modes, which Rings recreates.

Sympathetic strings. Some interesting string instruments (such as the sitar or sarod), make use of strings that are not directly struck/plucked by the musician, but which are just responding to vibration of the other strings, and add extra overtones or undertones to it. Rings simulates this phenomenon with a bunch of virtual strings (made with comb filters), allowing the addition of extra tones to an incoming audio signal. The tuning ratio between these strings can be altered.

Modulated/inharmonic string. This last method is perhaps the most f

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