O-Bells User Guide
Modal synthesis bell engine — from cathedral bells to gamelan shimmer
Getting Started
Quick Start
- Download the installer from the O-Bells product page
- Run the installer — it installs VST3, AU, and Standalone formats automatically
- Open your DAW and scan for new plugins, or launch O-Bells Standalone
- Insert O-Bells on a MIDI track
- Enter your license key (OUA-XXXX-XXXX-XXXX) when prompted
- Play notes using your MIDI controller or the built-in keyboard (Z-M and Q-P keys)
Tip: O-Bells is free — complete checkout with your email to receive your license key.
System Requirements
| Platform | Details |
|---|---|
| macOS | macOS 10.13+ (Intel and Apple Silicon native) |
| Windows | Windows 10+ (64-bit) |
| RAM | 4 GB minimum, 8 GB recommended |
| Formats | VST3, AU, Standalone |
| DAW | Any VST3/AU-compatible host |
Installation Paths
macOS:
- VST3:
~/Library/Audio/Plug-Ins/VST3/O-Bells.vst3 - AU:
~/Library/Audio/Plug-Ins/Components/O-Bells.component - Standalone:
/Applications/O-Bells.app
Windows:
- VST3:
C:\Program Files\Common Files\VST3\O-Bells.vst3 - Standalone:
C:\Program Files\Ouaricon Audio\O-Bells\O-Bells.exe
Interface Overview
O-Bells has two main tabs: Instrument and Tuning.
Instrument Tab
- Top Bar: Preset browser with navigation arrows, SAVE and LOAD buttons
- Synthesis Section: Core bell timbre controls — Damping, Overtone Brightness, Acoustic Brightness, Material, Inharmonicity, Air Absorption, Air Time
- Bloom Section: Bloom Speed/Amount and optional per-band Fine Controls (Low/Mid/High)
- Shimmer: Frequency modulation that increases during decay
- Ensemble Section: Unison voices, Detune, Sub-octave layer
- Footer: Gain slider, 2-octave MIDI keyboard (C3–B4), QWERTY key labels
Tuning Tab
- Interval Editor: 12-note interval table with per-note cent values
- Visualizations: Circle, Polar, Matrix, True Keys, and Rotation views
- Tuning Library: 24 embedded tunings across 5 categories
- A4 Reference: Adjustable reference frequency (400–480 Hz)
- Stretch: Octave stretch factor for physical modeling
- SCL/KBM: Import and export Scala tuning files
- Generate Scale: Built-in scale generator
Tip: Double-click any slider to reset it to its default value.
Synthesis Parameters
O-Bells uses modal synthesis with 8 partials to model the acoustic behavior of struck metal objects. These parameters shape the core timbre.
| Parameter | Range | Default | Description |
|---|---|---|---|
| Damping | 0–100% | 70% | Controls decay length. Low values produce hand-damped tones; high values let the bell ring freely. |
| Overtone Brightness | 0–100% | 50% | Sets the initial amplitude of upper partials. Higher values create a brighter, more brilliant attack. |
| Acoustic Brightness | 0–100% | 70% | Controls how quickly high frequencies decay relative to low ones. Lower values create a warmer, woody sound; higher values sustain the brightness. |
| Material | Bronze / Brass / Steel / Aluminum / Cast Iron | Bronze | Selects the acoustic material model, each with unique decay characteristics and tonal color. |
| Inharmonicity | 0–100% | 50% | Controls partial spacing. Low values produce pure, harmonic tones; high values create gamelan-style inharmonic partials characteristic of real bells. |
| Air Absorption | 0–100% | 0% | Progressive high-frequency rolloff during decay, simulating sound propagation through air over distance. |
| Air Time | 0.1–10.0 s | 2.0 s | Duration of the air absorption filter sweep. Longer times create a slower, more gradual darkening. |
Material Guide
- Bronze: Classic bell sound — rich overtones, warm sustain. Church bells, tubular bells, cymbals.
- Brass: Slightly brighter than bronze with a more focused fundamental. Hand bells, bowls.
- Steel: Bright and cutting with prominent upper partials. Steel pans, glockenspiel, vibraphone bars.
- Aluminum: Light and shimmery with fast decay. Wind chimes, small percussion.
- Cast Iron: Dark and heavy with strong low partials and slower attack. Large gongs, temple bells.
Bloom & Shimmer
Bloom controls create spectral swelling — partials that gradually grow in amplitude after the initial strike, giving the bell an evolving, living quality.
| Parameter | Range | Default | Description |
|---|---|---|---|
| Bloom Speed | 25–400 ms | ~212 ms | How quickly the bloom effect reaches its peak. Shorter times for percussive swell; longer for gradual evolution. |
| Bloom Amount | 0–100% | 0% | Intensity of the spectral swelling effect. At 0%, bloom is off. |
| Shimmer | 0–100% | 20% | Frequency modulation that increases during the decay phase. Adds metallic sheen and movement to sustained tones. |
Bloom Fine Controls (Override Mode)
Enable the checkbox to activate per-band bloom control. When active, the main Bloom Speed and Bloom Amount sliders are disabled and replaced by independent Low, Mid, and High band controls.
| Parameter | Range | Default |
|---|---|---|
| Speed Low | 15–250 ms | ~133 ms |
| Speed Mid | 25–400 ms | ~212 ms |
| Speed High | 50–800 ms | ~425 ms |
| Amount Low / Mid / High | 0–100% | 0% |
Tip: For realistic bell bloom, set a faster Speed Low and slower Speed High. This simulates how lower partials in real bells swell before higher ones.
Ensemble
The Ensemble section transforms single bell tones into rich, layered textures by stacking detuned voices and octave layers.
| Parameter | Range | Default | Description |
|---|---|---|---|
| Unison | 1–4 | 1 | Number of detuned bell copies per note. Each additional voice adds thickness and chorus-like movement. |
| Detune | 0–50 cents | 10 cents | Pitch spread between unison voices. Small values (5–10) for subtle thickening; larger values (20–50) for dramatic beating. |
| Sub | 0–100% | 0% | Blends in a sub-octave layer beneath the main tone. Adds weight and depth to the bell sound. |
Tip: Be mindful of polyphony when using high Unison counts. With 4 unison voices and 16-voice polyphony, you can sustain up to 4 simultaneous notes before voice stealing kicks in.
Advanced Controls
Strike & Mallet
| Parameter | Range | Default | Description |
|---|---|---|---|
| Strike Position | 0–100% | 50% | Where the mallet hits the bell. Center (0%) emphasizes the fundamental; edge (100%) brings out upper partials. |
| Mallet Hardness | 0–100% | 50% | Soft felt (0%) for warm, muted attacks; hard metal (100%) for bright, percussive transients. |
| Noise Character | Click / Thud / Ping | Click | Transient filter type shaping the initial strike noise. |
| Attack Amount | 0–100% | 50% | Volume of the strike transient relative to the tonal body. |
Decay Envelope
| Parameter | Range | Default | Description |
|---|---|---|---|
| Strike Time | 5–100 ms | 30 ms | Duration of the bright metallic transient at the start of each note. |
| Brilliance | 0–100% | 50% | High-frequency sustain. Low values create a warm, woody sound; high values maintain brightness through the decay. |
| Body Time | 100–5000 ms | 1500 ms | Duration of the main tonal decay phase. |
| Hum Sustain | 0–100% | 50% | Extends the sustain of the lowest partials. High values produce the long low hum characteristic of large bells. |
Character
| Parameter | Range | Default | Description |
|---|---|---|---|
| Humanize | 0–100% | 30% | Per-note random variation across strike position, mallet hardness, decay time, attack, and inharmonicity. Creates natural-sounding performances. |
| Nonlinear | 0–100% | 0% | Bell warping and distortion effects for more aggressive or unusual timbres. |
| Pitch Envelope | 0–100% | 0% | Initial pitch drop amount. Simulates the slight pitch bend that occurs when a large bell is first struck. |
| Pitch Env Time | 5–200 ms | 50 ms | How quickly the pitch returns to normal after the initial drop. |
| Velocity Curve | Linear / Exponential / Logarithmic | Linear | Response shape for MIDI velocity. |
Output
| Parameter | Range | Default | Description |
|---|---|---|---|
| Reverb | 0–100% | 30% | Built-in reverb mix for adding spaciousness. Optimized for bell timbres. |
| LP Filter | ON / OFF | OFF | Enables a one-pole lowpass filter on the output. |
| LP Cutoff | 200–20,000 Hz | 20,000 Hz | Lowpass filter cutoff frequency. Lower to tame brightness. |
| Gain | −24 to +12 dB | 0 dB | Master output level. |
| High Fidelity | ON / OFF | OFF | Disables voice culling for maximum quality. Higher CPU usage. |
Tuning System
The Tuning tab provides a comprehensive microtuning environment. Switch tabs at the top of the plugin window to access it.
Interval Editor
The left panel shows the 12-note interval table. Each note displays its offset in cents from the root. Click a value to edit it directly. Use the Tonic selector to change the root note.
Tuning Visualizations
- Circle: Pitch-class circle showing interval distribution around the octave
- Polar: Polar plot of interval ratios
- Matrix: Interval matrix showing all note-to-note relationships
- True Keys: Real-time interval analyzer showing note names, interval labels (m3, P5, etc.), and total span in cents
- Rotation: Rotational view of the scale structure
Tuning Library
O-Bells includes 24 embedded tunings across 5 categories:
Historical Temperaments
- Young 1799 — Thomas Young's well-temperament, balanced for all keys
- Neidhardt III — Johann Neidhardt's circulating temperament (1724)
- Kellner Bach — Herbert Kellner's reconstruction of Bach's tuning
- Bach/Lehman — Bradley Lehman's interpretation of Bach's WTC tuning
- Valotti — Francesco Valotti's temperament (c. 1754)
Just Intonation
- Ptolemy Intense Diatonic — Ancient Greek tuning with pure 5ths and 3rds
- 5-Limit JI — Pure major and minor triads in C
- 7-Limit JI — Includes septimal minor 7th (7/4)
- Partch 43-Tone — Harry Partch's 43-tone 11-limit scale
Equal Divisions (EDO)
- 17-EDO — Good Pythagorean approximation
- 19-EDO — Excellent meantone approximation
- 22-EDO — Good septimal intervals (7-limit)
- 31-EDO — Nearly pure 5ths and 3rds
- 41-EDO — Excellent 5-limit and 7-limit approximations
- 53-EDO — Nearly perfect 5ths, used in Turkish music theory
Non-Octave
- Bohlen-Pierce (Equal) — 13 equal divisions of the 3:1 tritave
- Carlos Alpha — Wendy Carlos' Alpha scale (78-cent steps)
- Carlos Beta — Wendy Carlos' Beta scale (63.8-cent steps)
- Carlos Gamma — Wendy Carlos' Gamma scale (35.1-cent steps)
World Tunings
- Arabic 24-TET — 24-tone equal temperament with quarter tones
- Turkish Makam — 53-comma based traditional tuning
- Indian 22-Shruti — Traditional 22-shruti system for raga intonation
- Gamelan Slendro — Javanese 5-tone approximately equal pentatonic
- Gamelan Pelog — Javanese 7-tone with characteristic narrow and wide steps
SCL/KBM Import & Export
Load and save tunings in the standard Scala format (.scl for scale, .kbm for keyboard mapping). This allows compatibility with thousands of community-created tuning files.
Scale Generator
The built-in scale generator can create equal divisions, just intonation grids, and other scale structures directly within the plugin.
Tuning Parameters
| Parameter | Range | Default | Description |
|---|---|---|---|
| A4 Reference | 400–480 Hz | 440 Hz | Concert pitch reference frequency. |
| Octave Stretch | 0.95–1.25 | 1.00 | Physical modeling octave stretch factor. Values above 1.0 widen the octave, as occurs naturally in some bell types. |
| Pitch Bend Range | 1–48 semitones | 2 semitones | MIDI pitch bend wheel range. |
Presets
O-Bells ships with 25 factory presets across 5 categories. Use the left/right arrows in the top bar to browse, or click the preset name to open a dropdown.
Large Bells
| Preset | Description |
|---|---|
| Deep Bronze Tower | Massive tower bell with deep bronze character and long sustain |
| Massive Iron Bell | Heavy cast iron bell with dark, weighty tone |
| Cavernous Brass | Large brass bell with spacious reverberant quality |
| Grand Cathedral Bell | Full-sized cathedral bell with rich harmonics and hum |
| Slow Tolling Bell | Slow-decaying toll with gradual bloom and shimmer |
Bright Bells
| Preset | Description |
|---|---|
| Bright Clear Crotale | Small, bright pitched percussion with clean sustain |
| Crystalline Steel Chime | Bright steel chime with sparkling upper partials |
| Sparkling Aluminum | Light aluminum with fast, shimmery decay |
| Brilliant Bronze Plate | Bright bronze with prominent overtones |
| Crisp Steel Bar | Tight, focused steel bar tone |
Warm Bells
| Preset | Description |
|---|---|
| Soft Mallet Bronze | Soft felt mallet on bronze for warm, gentle tones |
| Mellow Brass Bowl | Singing bowl character with smooth, centered sound |
| Warm Aluminum Bars | Muted aluminum with rounded, mellow quality |
| Gentle Hand Bell | Small hand bell with delicate, warm character |
| Velvet Bronze Tone | Soft, dark bronze with minimal upper partials |
Metallic
| Preset | Description |
|---|---|
| Dense Bronze Gamelan | Gamelan-style inharmonic bronze with characteristic beating |
| Clanging Steel Plate | Bright, aggressive steel plate with complex overtones |
| Beating Bronze Gong | Large gong with slow beating partials and shimmer |
| Shimmering Bell Tree | Cascading bell tree with multiple bright layers |
| Dark Iron Resonance | Heavy iron with dark, resonant metallic character |
Ambient
| Preset | Description |
|---|---|
| Distant Cathedral | Far-away bell with heavy air absorption and reverb |
| Underwater Bell | Filtered, submerged quality with slow evolution |
| Evolving Bronze Wash | Long bloom creating evolving pad-like textures |
| Frozen Steel Shimmer | Bright, frozen steel with heavy shimmer and sustain |
| Ethereal Chime Pad | Pad-like layered chimes with ensemble and bloom |
Managing Presets
Use the SAVE button to store your own presets. Use LOAD to browse and import preset files.
Presets are stored at:
macOS: ~/Library/O-Bells/Presets/
Windows: %APPDATA%\O-Bells\Presets\
Troubleshooting
Plugin Not Appearing in DAW
- Rescan your plugin directories in your DAW's preferences
- Verify the plugin is installed at the correct path (see Installation Paths above)
- On macOS, check that Gatekeeper hasn't blocked the plugin (System Settings → Security & Privacy)
- Restart your DAW after installation
No Sound
- Ensure the plugin is on a MIDI track and receiving MIDI input
- Check that Gain is above −24 dB
- Verify your MIDI controller is connected and sending notes
- Try clicking the built-in keyboard or pressing Z–M keys
High CPU Usage
- Reduce Unison count (each voice multiplies CPU cost)
- Disable High Fidelity mode if enabled
- Watch the decay warning — long decays with high polyphony can be CPU-intensive
- Reduce polyphony by using shorter Body Time or higher Damping
- Check your DAW's buffer size settings — increase if needed
Tuning Not Loading
- Verify your .scl file uses standard Scala format with valid cent or ratio values
- Check that the .kbm file references the correct number of scale degrees
- Try loading one of the built-in tunings from the Tuning Library first to confirm the system works
Decay Warning
If you see "Estimated bell decay: ~Ns. Long decays with polyphony may cause high CPU usage, distortion, or stuttering", consider reducing Damping, Body Time, or Hum Sustain. Alternatively, reduce polyphony by playing fewer simultaneous notes.