ModalResonator (mono / stereo)

A modal synthesis resonator bank inspired by Mutable Instruments Rings and Elements. Takes any incoming audio as an exciter — a trigger burst, a noise pulse, a percussive transient, or external audio — and uses it to “strike” a bank of 12 parallel resonant bandpass filters tuned to a modal spectrum. The filters ring at their natural frequencies and decay over time, producing metallic chimes, struck bars, tuned bowls, plucked bodies, and glassy sustain tones.

Because the resonator is a processor, not a source, it preserves full V/Oct tracking and can be driven by any signal in the chain above it.

Signal flow 

input ──► AudioEffectModalResonator (wet path) ─┐
input ──────────────────────────────────── (dry) ┴──► AudioMixer ──► output

Parameters

Freq — Fundamental frequency

The pitch of the lowest resonator (mode 0). All other modes are tuned relative to this frequency according to the Structure parameter.

  • Note name cursor: Adjusts pitch in semitone steps. Displays the closest chromatic note name.
  • Hz cursor: Fine-tunes pitch in ~3-cent steps.
  • Freq CV: V/Oct pitch CV input. Pitch CV is sampled continuously — no trigger required.

At Structure = 0 (harmonic), Freq sets the true fundamental of a complete harmonic series. At Structure = 100 (inharmonic), Freq sets the lowest partial; the others are spread above it in an inharmonic pattern and the perceived “pitch” may feel higher.

Inh — Inharmonicity (0–100)

Controls the spectral stiffness of the modal bank — how partials are spaced relative to the fundamental. The model uses an additive stretch algorithm (inspired by Mutable Instruments Rings) rather than a simple harmonic series.

Value Behaviour
0 Negative stiffness — partials compressed below the fundamental, descending cluster
~3 Stiffness ≈ 0 — true harmonic series: f, 2f, 3f, 4f … → string, organ
25 Slightly stretched overtones → acoustic piano character
50 (default) Moderately stretched → marimba, wooden bars
75 Strongly inharmonic → steel tongue drum, bell plates
100 Maximally stretched → bell, bowl, gong

Low Inharmonicity (0–10): At Inh=0 the stiffness is slightly negative, meaning upper partials are tuned below the fundamental frequency in a compressed descending cluster. This produces dense, dark, gamelan-like tones rather than a bright harmonic series. Because the partials shift from below the fundamental to above it as Inharmonicity increases, sweeping from 0 upward creates a noticeable perceived pitch shift — this is expected behaviour, not a tuning error. For a conventional harmonic series, use Inh≈3.

Inh CV offsets the value; full positive swing pushes toward maximally stretched.

Sweeping Inharmonicity with a slow CV while the resonator is ringing produces a continuous timbral morph — the spectrum reorganises around each new set of partials.

Brt — Brightness (0–100)

Controls the amplitude taper across the mode bank — how much energy is present in the upper modes compared to the fundamental.

Value Behaviour
0 Only mode 0 sounds; all upper modes are suppressed → deep, fundamental-only tone
50 Moderate rolloff; the first few partials are audible
100 All 12 modes have equal weight → full spectral richness, bright and present

Brt CV offsets the value. Modulating Brightness while a note decays creates a timbral evolution as the sound rings out.

High brightness with long decay (Dmp near 100) produces very dense, shimmering sustain. Low brightness with long decay produces a pure, sine-like tone.

Dmp — Damping (0–100)

Controls the decay time of all resonators — the rate at which the ringing fades to silence.

Value Approximate RT60 Character
0 ~10 ms Metallic click, percussive tap
25 ~100 ms Short clink, cowbell-like
50 ~300 ms Medium chime
75 ~700 ms Bell, long shimmer
100 ~2 s Near-infinite sustain, glass harmonica

Higher modes decay slightly faster than lower modes regardless of Dmp, which is consistent with the natural behaviour of physical resonant structures.

Dmp CV offsets the value; sweeping from 0 to full swing covers click to sustain.

Damping can be CV-automated for per-note variation: short decays on percussive triggers, long decays on held notes.

Pos — Position (0–100)

Specifies the excitation point on the virtual resonant structure, creating a comb-filtering effect by selectively suppressing certain harmonics. This is the same mechanism used in Mutable Instruments Rings.

Value Behaviour
0 No notching; all modes receive equal excitation energy
25 (default) Mild comb; upper modes slightly attenuated
50 Strong comb at halfway — even-numbered harmonics are suppressed (odd-harmonic spectrum)
75 Comb at three-quarters — a different set of partials notched
100 Approaches no-notching again (full period)

Pos CV sweeps the excitation point continuously. Modulating Position rhythmically with an LFO produces a timbral tremolo effect where alternating sets of partials rise and fall.

Position interacts strongly with Structure. At Str = 0, Position produces recognisable open/muted-string timbres. At Str = 100, the notch pattern affects a dense inharmonic spectrum and produces more unpredictable tonal colouring.

Mix — Wet/dry balance (0–100%)

Blends the resonated signal (wet) with the unprocessed input (dry) using equal-power crossfading.

Value Behaviour
0% Fully dry — input passes through unaffected
50% Equal blend — both the exciter and the resonance are audible
100% (default) Fully wet — only the resonated output is heard

Mix CV offsets the value. Setting Mix to 50% and automating with a slow LFO creates a tremolo effect between the raw exciter and the resonant tail.

VU meters

Two small bars sit at the top of the display:

  • Top bar (filled) — peak level of the incoming exciter signal. Confirms that the resonator is being driven: no bar = no excitation; full bar = heavy continuous driving.
  • Bottom bar (outline) — peak level of the resonator’s wet output, post-filtering. Use this to gauge how much the resonator is ringing relative to the excitation.

The two bars together show whether the resonator is building up energy (output bar growing) or decaying (output bar shrinking while excitation bar is low).

Trg — Gate trigger input

The Trg parameter (visible when cursor scrolls past Mix) accepts an assignable gate input. A rising edge on the assigned jack fires a noise-burst strike at the current Vel setting. Use this to clock the resonator from a sequencer, envelope gate, clock divider, or any other trigger source in the patch.

The Trg label inverts (white-on-black) while the gate is held high, giving a clear visual indication of the gate state.

To assign: navigate to the Trg row, press the encoder button, then select the input jack from the map editor.

Vel — Strike velocity (0–100%)

Sets the base amplitude of noise-burst strikes fired by the Trg gate input. 100% = full amplitude; lower values produce softer, quieter strikes.

Vel CV adds a CV offset on top of the base value, clamped to 0–100%. This allows per-note velocity from a MIDI controller or a sequencer’s accent CV output.

AuxButton strikes always fire at 100% velocity regardless of the Vel setting.

AuxButton — Manual strike

Pressing the Aux button fires a white-noise burst directly into the resonator at full amplitude (100% velocity). This is useful for auditioning the sound without a patched exciter, or for manually triggering a transient during performance.

The noise burst is one audio block (~2.7 ms) long — short enough to be a clean impulse at most decay settings.

Both Trg and AuxButton can be active simultaneously — either source triggers the strike.

Suggested patches

Tuned metallic percussion

  • Set Inh = 70–80 (bell/bar), Damping = 40–60, Brightness = 80.
  • Drive with a short trigger from a clock divider or a drum sequencer gate.
  • V/Oct from a sequencer tracks melodic lines across the bar spectrum.

Glass harmonica / singing bowl

  • Set Inh = 0 (harmonic), Damping = 90, Brightness = 50, Position = 50.
  • Drive with a slow, low-amplitude sine or triangle LFO (continuous light excitation).
  • The resonator sustains indefinitely and the position comb creates an airy, filtered tone.

Plucked body tone (Rings-style)

  • Set Inh = 10–20 (near-harmonic), Damping = 55, Brightness = 65, Position = 25.
  • Trigger with a V/Oct sequencer gate. Mix = 100%.
  • Varies the pitch quickly for chord arpeggios.

Chime cluster

  • Place two ModalResonator applets on L and R channels.
  • Tune them slightly apart (1–3 semitones). Set both to Structure = 60, Damping = 75.
  • Drive with the same trigger source. The two inharmonic spectra beat against each other producing a thick, shimmering cloud.

Timbral sweep

  • Lock a note with AuxButton or a held gate.
  • Slowly sweep Inharmonicity from 0 to 100 with a slow envelope or LFO on Inh CV.
  • The spectrum morphs continuously from a pure string tone to a metallic bell.

Percussive body resonance insert

  • Set Mix = 40–60%, Damping = 15–25 (short decay), Structure = 50.
  • Route a snare or tom through the applet.
  • The resonator adds a metallic body-ring sympathetically tuned to each hit.

Technical notes

  • The resonator bank consists of 12 parallel Chamberlin state-variable filters (SVF bandpass). Each mode has its own frequency coefficient, damping, and gain weight.
  • All trigonometric coefficient computation (powf, cosf, sinf) runs at control rate (~150 Hz) in Controller(). The audio interrupt loop (update()) contains only multiply-accumulate operations — no trig in the hot path.
  • A single-pole DC blocker (pole at z = 0.995) is applied to the summed output.
  • Mode frequencies are clamped below ~17.6 kHz (40% of Nyquist) to maintain SVF filter stability margin. Clamping at exactly 20 kHz left only 0.7% headroom below the instability boundary; the lower ceiling provides ~5% margin.
  • The applet is available in slot 0 (input slot) and all processor slots, in both mono and stereo configurations.
  • Memory footprint: approximately 400 bytes per active channel instance — no heap allocation.
  • Extreme parameter combinations: High Str (80–100) combined with high Dmp (80–100) and very low Brt (0–15) pushes upper filter modes near the Nyquist frequency with minimal damping. This is at the stability boundary of the resonator filter and produces harsh, noisy transients rather than clean tones. These settings are usable for deliberate textural noise effects but are not intended as musical resonator sounds.

Credits

DSP architecture inspired by Mutable Instruments Rings (Émilie Gillet). ModalResonatorApplet is an independent reimplementation and does not use any Mutable Instruments source code.

Authored by Andy Jenkinson ‘uglifruit’ — using ClaudeCode. DSP core (AudioEffectModalResonator) and applet wrapper (ModalResonatorApplet) released under the MIT License.

MIT License
Copyright (c) 2026 Andy Jenkinson

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