PartialString

Free Physical Modeling Synth That Simulates Real String Vibrations

PartialString is a free physical modeling synthesizer developed by Different Instruments. Rather than relying on samples, wavetable oscillators, or virtual analog synthesis, it generates sound by numerically simulating the vibration of a plucked string in real time using the Finite-Difference Time-Domain (FDTD) method.

Available for macOS, Windows, and Linux, PartialString offers an educational yet highly musical approach to sound synthesis, allowing producers and sound designers to explore the physics behind string instruments while creating everything from realistic plucks to lush evolving pads and experimental textures.

What Is PartialString?

At its core, PartialString is a physical modeling synthesizer.

Instead of replaying recorded audio or approximating string behavior with filters and oscillators, it continuously calculates how a virtual string vibrates after being excited.

Every note is generated from the mathematical simulation itself.

This means the instrument reacts naturally to changes in:

• Excitation position
• Pickup location
• String length
• Damping
• Simulation accuracy

The result is an instrument that feels dynamic and expressive, with subtle variations that are difficult to achieve using sample-based synthesis.

Finite-Difference Time-Domain (FDTD) Modeling

PartialString uses the Finite-Difference Time-Domain (FDTD) method to solve the one-dimensional wave equation in real time.

Rather than treating the string as a single oscillator, the plugin divides it into many tiny points stored in memory.

When the string is plucked:

1. A displacement is introduced.
2. The simulation calculates how that energy propagates.
3. A virtual pickup reads the movement.
4. The resulting vibration becomes the audio output.

Because the simulation follows the physics of a vibrating string, the sound evolves naturally instead of looping or repeating predefined samples.

Adjustable Excitation

One of PartialString’s most expressive features is its customizable string excitation.

You can control:

• Pluck position
• Excitation shape
• Velocity sensitivity

Changing where the string is plucked dramatically affects the harmonic content, much like playing a real guitar, harp, or piano string.

This allows for a wide range of tonal variations using the same underlying model.

Pickup Position Modulation

Instead of moving the string itself, PartialString also lets you move the virtual pickup.

An integrated LFO can continuously sweep the pickup position across the string.

At slower speeds, this creates subtle tonal movement similar to changing the listening position on a physical instrument.

At audio-rate modulation speeds, it introduces complex sidebands and AM-like textures that push the synth into far more experimental territory.

Adjustable Decay and Dampers

Decay can be shaped in multiple ways.

The virtual string can ring freely for long periods or be damped to produce tighter, more percussive sounds.

The dampers can even behave similarly to those of a piano, automatically muting the string after the note ends.

Combined with long decay settings, PartialString can generate surprisingly lush sustained sounds that resemble evolving pads rather than traditional plucked instruments.

Simulation Accuracy

One of the most unusual controls is Model Accuracy.

Reducing the simulation accuracy intentionally introduces artifacts that move away from realistic physics.

Lower settings produce:

• Softer attacks
• Inharmonic overtones
• Unusual resonances
• Dreamlike textures

Accuracy can remain constant across all notes or scale according to string length to balance realism and CPU usage.

This transforms PartialString from an educational physical model into a creative sound design tool.

Dynamic Polyphony

PartialString supports up to 10 voices of polyphony.

However, unlike most software instruments, the available voice count automatically adjusts depending on:

• The pitch being played
• String length
• CPU performance

Lower notes require longer simulated strings, making them significantly more computationally demanding.

Rather than causing audio glitches or dropouts, the plugin intelligently reduces the number of simultaneous voices when necessary.

On slower computers, very low notes may behave monophonically or be automatically shifted up by one or two octaves to maintain stable real-time performance.

Performance Optimization

Physical modeling is computationally intensive, especially when simulating long strings.

PartialString includes several features to keep the instrument responsive:

• Automatic voice management
• Optional low-note limiting
• Automatic octave shifting for demanding notes
• Adjustable simulation accuracy

When rendering or bouncing tracks offline, these real-time performance restrictions are bypassed, allowing full-quality exports.

Apple Silicon users are also advised to run a native ARM version of their DAW, as using Rosetta 2 translation can noticeably reduce performance.

Cross-Platform Support

PartialString is available for:

macOS

• AU
• VST3
• Intel & Apple Silicon
• macOS 10.13+

Windows

• VST3
• Windows 10 or later (64-bit)

Linux

• VST3 (x86-64)

The plugin is offered as freeware, with an optional pay-what-you-want donation model.

Best Uses

PartialString is particularly well suited for:

Physical Modeling Synthesis

Explore the behavior of vibrating strings without relying on samples.

Ambient Music

Long decays and moving pickups create evolving harmonic landscapes.

Cinematic Scoring

Generate expressive plucks, resonant drones, and organic textures for film and game soundtracks.

Experimental Sound Design

Lower simulation accuracy produces unusual, inharmonic timbres ideal for modern electronic music.

Education

Because the interface visualizes the vibrating string, PartialString is also an excellent learning tool for understanding wave propagation and physical modeling synthesis.

Strengths

✅ True finite-difference physical modeling

✅ Dynamic and expressive string behavior

✅ Adjustable excitation and pickup positions

✅ Audio-rate pickup modulation

✅ Creative inharmonic modes via reduced accuracy

✅ Cross-platform support (Windows, macOS, Linux)

✅ Free with optional donation

Weaknesses

❌ CPU usage increases significantly for low notes

❌ Dynamic polyphony may surprise users expecting fixed voice counts

❌ Focused on plucked string synthesis rather than a wide range of instrument types

❌ Physical modeling workflow has a steeper learning curve than sample-based instruments

Final Verdict

PartialString is one of the most technically impressive free synthesizers released in recent years. By solving the wave equation in real time with finite-difference methods, it delivers an authentic physical modeling experience that goes far beyond conventional virtual instruments.

Equally suited to realistic plucked strings, evolving ambient pads, and experimental inharmonic sound design, it rewards curiosity and experimentation. The addition of visual string feedback, pickup modulation, adjustable simulation accuracy, and intelligent performance management makes it both an educational tool and a genuinely inspiring instrument for music production.

For producers interested in the science of sound—or simply looking for something refreshingly different from another subtractive synth—PartialString is an outstanding free download.

Source : differentinstruments.com/