FILTRONIX VST Plugin

Analog character without losing control.

FILTRONIX combines circuit-inspired filtering with modern DSP techniques for smooth resonance, controllable drive, and practical mix-ready operation.

Circuit modeling

Model the behavior

Filter topology, feedback, saturation, and resonance interact as one system instead of a stack of unrelated effects.

ZDF / TPT

Keep resonance responsive

Zero-delay feedback topology supports smooth cutoff movement and stable behavior at high resonance.

Nonlinear drive

Add tone with clarity

ADAA saturation and 4x oversampling help control aliasing while the Drive stage adds weight and edge.

Visual feedback

See the filter move

The spectrum and response display make cutoff, resonance, and tonal changes easy to follow.

Four circuits. Four personalities.

Switch filter character without rebuilding your processing chain.

M-Filter

Transistor ladder

A pronounced resonant peak with the familiar musical low-end movement of a classic ladder response.

S-Filter

Classic state variable

A thick, focused response that keeps weight around strong resonance and near self-oscillation.

P-Filter

Polyphonic OTA

A fat and punchy cascade character inspired by the sound of classic polyphonic instruments.

W-Filter

British CMOS

An unstable, aggressive response with sudden resonance and a distinctly raw circuit character.

Why ZDF / TPT matters.

The feedback loop is central to how an analog filter responds when cutoff and resonance are pushed.

Delayed feedback

A digital compromise

A unit delay inside the feedback path can change the response and make extreme resonance feel less connected.

Zero-delay feedback

A tighter circuit response

ZDF / TPT solves the feedback relationship within the current sample for smoother control and more analog-like interaction.

FILTRONIX combines ZDF / TPT filtering with nonlinear saturation, 4x oversampling, and a phase-compensated 33-tap FIR polyphase stage.

Analog movement, not static perfection.

The Analog control introduces subtle variation that makes the filter feel less mechanically identical from moment to moment.

Cutoff drift: subtle movement around the selected frequency.
Resonance variation: small changes in feedback behavior.
Crosstalk: controlled interaction that adds width and imperfection.
Input-sensitive saturation: more level produces more character.

Signal flow

Audio input
  |
Input + Drive
  |
Circuit-modeled ZDF filter
  |
ADAA saturation + oversampling
  |
Mix + Output
  |
Audio output

A practical filtering workflow.

Start clean, choose the circuit character, then add movement and drive only where the source needs it.

Choose a filter model

Start with M, S, P, or W according to the resonance shape and tonal weight you want.

Set cutoff, resonance, and slope

Shape the frequency range, then switch between 12dB and 24dB operation for a gentler or steeper response.

Add Drive and Analog

Push the nonlinear stage for tone, then add subtle movement without losing the core filter setting.

Level-match and compare

Use Output, Mix, and Bypass to compare the processed sound at a fair level.

Useful across modern production.

Use FILTRONIX as a precise tone shaper, a resonant sound-design tool, or a driven analog-style color stage.

Synths and keys

Shape bright oscillators, pads, and sequences with circuit-specific resonance and movement.

Drums and bass

Control upper-frequency energy while adding weight, drive, and rhythmic filter motion.

Loops and effects

Create sweeps, transitions, and unstable textures from static samples and effect returns.

Automation

Move cutoff and resonance with a responsive topology designed for musical modulation.

Controls and specifications.

Product: FILTRONIX
Version: 1.1.1
Type: Circuit-modeled low-pass filter effect
Filter models: M, S, P, W
Topology: Zero-Delay Feedback / TPT
Slope: 12dB / 24dB switchable
Processing: 4x oversampling, 33-tap FIR polyphase, ADAA saturation
Controls: Input, Drive, Mix, Output, Cutoff, Resonance, Analog, Model, Slope, Bypass
Formats: Windows VST3 / macOS AU
Price: Free download

Installation.

Install FILTRONIX in the standard plug-in folder for your platform, then rescan plug-ins in your DAW.

Windows

VST3

Copy the FILTRONIX VST3 bundle to the standard VST3 folder, then rescan in your host.

C:Program FilesCommon FilesVST3

macOS

Audio Unit

Copy the FILTRONIX component to your user or system Components folder, then restart or rescan your DAW.

~/Library/Audio/Plug-Ins/Components

macOS AU builds target Apple Silicon and Intel Mac. Intel Mac compatibility remains under verification. If Gatekeeper blocks the component, check Privacy & Security and rescan Audio Units.

FAQ

What makes FILTRONIX different from a standard digital filter?

FILTRONIX models circuit-inspired feedback and nonlinear behavior, then combines it with ZDF / TPT topology, saturation, and oversampling.

Which filter model should I try first?

Start with M for a familiar ladder-style response, then compare S, P, and W at the same cutoff and resonance settings.

What does the Analog control change?

It adds subtle cutoff drift, resonance movement, crosstalk, and input-sensitive saturation for a less static response.

Why use 4x oversampling?

Oversampling gives nonlinear processing more internal bandwidth and helps reduce audible aliasing when Drive and resonance are pushed.

Is FILTRONIX free?

Yes. FILTRONIX is available as a free download for Windows VST3 and macOS AU.

Start filtering.

Download FILTRONIX and explore four circuit characters, nonlinear drive, and analog-style movement.

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