Mutable Instruments Rings User Manual

Mutable Instruments | Rings

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.

Rings is designed for Eurorack synthesizer systems and occupies 14 HP of space. It requires a -12V /
+12V supply (2x5 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.

This device complies with part 15 of the FCC Rules. Operation is subject to the following
two conditions: (1) This device may not cause harmful interference, and (2) this device must
accept any interference received, including interference that may cause undesired
operation.

This device meets the requirements of the following standards: EN55032, EN55103-2,
EN61000-3-2, EN61000-3-3, EN62311.

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:

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Mutable Instruments | Rings

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.

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.

This last method is perhaps the most familiar (in appearance!), since it is based on the extended Karplus­Strong method: the excitation signal is sent to a comb filter with an absorption filter, simulating the multiple
reflection of a wave propagating on a string and being absorbed at its ends. However, to bring more
variety to the sound, Rings adds three extra ingredients to this classic: a delay-compensated all-pole
absorption filter creating more drastic plucking effects, delay time modulation emulating the sound of
instruments with a curved bridge (like the sitar or tanpura), and all-pass filters in the delay loop, shifting
the position of the partials and recreating the tension of piano string or completely bonkers inharmonic
timbres.

Ideally, Rings would need three input signals:

A trigger signal on the STRUM input, which indicates that the currently playing note should fade away, and
that a new note is starting.

A CV signal on the V/OCT input, which controls the frequency of the note.
An audio signal on the IN input, which will hit, strike or caress the resonator.

Because it might not always be possible to get these three signals in your setup, Rings makes the
following assumptions:

First, if nothing is patched in the IN audio input, the module will synthesize an excitation signal whenever a
note is strummed. This excitation signal is either a low-pass filtered pulse, or a burst of noise depending
on the resonator type.

Secondly, if nothing is patched in the STRUM audio input, the module will determine that a new string
should be strummed either by:

Detecting note changes on the V/OCT input, or
Detecting sharp transients within the IN audio signal if nothing is patched in the V/OCT input.

If there should be one take-home (take-to-the-studio?) message from this, it is that you can perfectly play
Rings with just one CV output taken from a sequencer or S&H module: the note changes on the CV input
will be interpreted as note changes; and the module will produce a suitable excitation signal internally for

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