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Cover image for Studio Violin: Building a Physically Modelled Bowed-String Instrument in Instrudio
Gary Doman/TizWildin
Gary Doman/TizWildin

Posted on • Originally published at github.com

Studio Violin: Building a Physically Modelled Bowed-String Instrument in Instrudio

#music #webdev #audio #javascript

Studio Violin: Building a Physically Modelled Bowed-String Instrument in Instrudio

I’m building Instrudio, a browser-based virtual instrument ecosystem, and the flagship instrument right now is Studio Violin.

Studio Violin is a physically modelled bowed-string instrument built around Helmholtz motion synthesis, H2 harmonic correction, inharmonicity modelling, Stradivari-style body resonances, sympathetic open-string resonance, and live MIDI control.

The goal is not just to make a violin-like web instrument. The goal is to prove that a single version-controlled instrument definition can drive synthesis, UI, MIDI routing, plugin bridge behavior, presets, and live update propagation from one source of truth.

What Studio Violin does

Studio Violin models the behavior of a bowed violin string using a synthesis chain designed around acoustic measurements and practical browser audio constraints.

The instrument includes:

  • Helmholtz bowed-string waveform synthesis
  • H2 correction oscillator
  • Inharmonicity chorus per string
  • 8-band Stradivari-style body EQ
  • Per-string tonal offsets
  • Sympathetic open-string resonance
  • Nonlinear bow coupling
  • Pressure-coupled vibrato
  • Interval-scaled portamento
  • Bow-pressure, bow-speed, bow-point, character, brightness, attack, and vibrato controls
  • External MIDI routing through the Instrudio app

Synthesis model

The Helmholtz waveform uses a Fourier-style bowed-string model:

bₙ = −(2 / (n²π²D(1−D))) · sin(nπD)
D = 0.5 + bowPressure × 0.30
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The H2 correction oscillator is used to bring the second harmonic closer to the target H2/H1 balance measured in bowed-string acoustic research.

Studio Violin also includes per-string inharmonicity spread:

G = 0.00035
D = 0.00028
A = 0.00022
E = 0.00018
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The result is a sound engine that behaves less like a static sample trigger and more like a continuously controlled bowed instrument.

Stradivari-style body resonances

The body EQ model uses eight resonance bands:

A0: 275 Hz
A1: 475 Hz
B1−: 530 Hz
B1+: 580 Hz
Bridge hill: 2800 Hz, Q = 6.5
Upper resonance: 4500 Hz
Notch: 1100 Hz
Warmth: 180 Hz
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There are also per-string offsets:

G string: warmer, reduced bridge hill
E string: brighter, boosted bridge hill
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This lets the instrument react differently across the G, D, A, and E strings instead of applying one flat tone curve to the whole range.

Sympathetic resonance

Studio Violin includes sympathetic resonance using four triangle oscillators tuned to the open strings.

Amplitude = (1 − cents / 20) × 0.038
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The closer the played note is to an open-string relationship, the stronger the sympathetic contribution becomes.

Expressive controls

The instrument exposes controls for:

  • Bow pressure
  • Bow speed
  • Bow point
  • Vibrato rate
  • Vibrato depth
  • Attack
  • Brightness
  • Reverb
  • Volume
  • Playing character

Character modes include:

  • Solo
  • Bowed
  • Pizzicato
  • Col Legno
  • Tremolo
  • Spiccato

It also includes scale helpers such as G Major, D Major, A Minor, and Chromatic.

Signal chain

The current signal chain is:

PeriodicWave oscillator
→ H2 oscillator
→ chorus oscillators
→ WaveShaper
→ injection gain
→ warm shelf
→ 8 peaking body EQ bands
→ master output
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Single-source-of-truth instrument architecture

The bigger architecture behind Instrudio is the part I’m most excited about.

Studio Violin is driven by a single JSON definition file. That one definition can drive:

  1. The web audio synthesis engine
  2. The instrument UI
  3. External MIDI CC routing
  4. Note mapping
  5. Plugin bridge event protocol
  6. Preset management
  7. Live auto-update propagation across connected outlets

The runtime uses a remote-first fetch strategy, so definition changes pushed to GitHub can propagate to connected running instances within the cache TTL window.

The default TTL is currently 5 minutes.

Runtime metrics

Instrudio also includes live evaluation metrics for the single-source-of-truth runtime.

The metrics panel can display:

  • SSOT fetch latency
  • Definition apply time
  • Remote source availability
  • MIDI pipeline latency

These are captured with high-resolution timing through performance.now().

Metrics are also available programmatically through:

InstrudioSSOTRuntime.getMetrics()
InstrudioMIDI.getLatencyMetrics()
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Why this matters

A lot of virtual instruments are either sample libraries, closed plugin binaries, or isolated web toys.

Instrudio is aiming for something different:

  • web-first instruments
  • version-controlled definitions
  • measurable runtime behavior
  • MIDI-aware performance
  • bridgeable plugin architecture
  • open development
  • fast iteration without redeploying every outlet manually

Studio Violin is the flagship proof-of-concept for that architecture.

Repo

https://github.com/GareBear99/Instrudio

Feedback wanted

I’m looking for feedback from:

  • audio developers
  • Web Audio developers
  • musicians
  • violinists
  • producers
  • plugin developers
  • MIDI users
  • people interested in physical modelling

Useful feedback includes:

  • browser and OS
  • MIDI device behavior
  • latency
  • tone realism
  • UI feel
  • control response
  • broken notes or stuck notes
  • console errors
  • ideas for the next instrument model

Studio Violin is the flagship instrument in Instrudio, and I’m building it in public.

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