Equalizer APO is an open-source parametric and graphic equalizer for the Microsoft Windows operating system. It applies digital filters and effects to the audio streams coming out of or going into a computer.
Unlike traditional audio software, Equalizer APO does not run as a visible application on your desktop. It operates in the background as a native system service.
The software integrates directly into the Windows audio pipeline. It uses the Audio Processing Object framework, which Microsoft introduced in Windows Vista. Because of this design, the software applies audio filters before the digital signal reaches your speakers, headphones, or microphone. This keeps processing latency low and uses very little CPU power.
The background engine is controlled by a single plain text file named config.txt. When you edit this text file, the engine reloads the rules immediately. You do not need to restart your computer or your audio player to hear the changes.
Preamp: -6 dB
Filter: ON PK Fc 1000 Hz Gain 3 dB Q 1.4
Jonas Thedering registered the Equalizer APO project on SourceForge on September 13, 2012. At the time, Windows users had few practical options for applying system-wide equalization. Most solutions required virtual audio cables or custom sound card drivers. These older methods often caused audio latency, dropped samples, and system instability.
Thedering decided to build a tool that worked with the native operating system rather than against it. By writing a program that hooked directly into the Windows system effects framework, he created a stable way to apply audio correction to any connected hardware.
Jonas Thedering, who also appears in the project files as Jonas Dahlinger, is the creator and lead developer of Equalizer APO. He wrote the original C++ codebase and continues to manage the project repository and binary releases on SourceForge.
The project has evolved through several key milestones since its launch.
In February 2013, version 0.7 introduced the Device command, which let users apply different equalizer curves to different hardware outputs.
September 2015 marked a major milestone with the release of version 1.0. This update added the visual "Configuration Editor," the GraphicEQ command, and a native convolution engine for loading impulse response files.
Between 2017 and 2020, the software gained Alexander Walch's loudness correction filter and added support for Voicemeeter Potato.
From early 2024 to early 2025, a series of updates addressed modern operating system requirements. These updates resolved Bluetooth headset issues on Windows 11, introduced native Windows on ARM (ARM64) support, and added high-DPI scaling. Version 1.4 replaced the old setup tool with a modern "Device Selector" utility that supports Windows dark theme.
Equalizer APO is licensed under the GNU General Public License version 2.0 (GPLv2). The code is entirely public, allowing developers to inspect it, build their own copies, or propose bug fixes.
While the primary releases are hosted on SourceForge, the community has created multiple mirrors and custom forks on GitHub to experiment with double-precision processing and alternative build pipelines.
Jonas Thedering maintains the main software repository, but a small group of community volunteers handles daily operations. Peter Verbeek, Juha, and Etienne Dechamps moderate the SourceForge forums and help users troubleshoot installation issues on different hardware configurations.
The community also contributes directly to the software. Alexander Walch wrote the loudness correction filter that was integrated into version 1.2. In early 2025, version 1.4.2 added French and Simplified Chinese translations created by community members.
Equalizer APO uses a simple text file for its configuration, which has allowed other developers to build visual interfaces on top of it.
Peace Equalizer: Created by Peter Verbeek, Peace is the most popular companion tool. It adds an interactive mixing console with traditional frequency sliders, profile hotkeys, and automated setup tools.
HeSuVi: This project uses Equalizer APO's convolution engine to emulate 7.1 surround sound on stereo headphones.
Calibration Tools: The software works closely with external calibration programs. AutoEq, a database of headphone correction curves, generates text files designed to load directly into Equalizer APO. Users can also import measurement data from Room EQ Wizard to correct room acoustics.
There are a few technical realities and common misunderstandings about Equalizer APO:
ASIO and WASAPI Exclusive Mode: Equalizer APO does not work with these interfaces. ASIO and WASAPI Exclusive Mode bypass the Windows system mixer to send raw audio directly to your hardware, which prevents the APO framework from applying filters.
VST3 Support: The releases only support VST2 plugins. It does not support VST3 plugins natively.
Peace Equalizer Bundling: The software does not come bundled with Peace Equalizer. They are separate programs. You must install Equalizer APO first, then download and install Peace Equalizer separately.
Paid Versions: The project is completely free. There are no paid tiers or donation links. An unauthorized paid version appeared on the Microsoft Store in late 2023 under the publisher name "Niente." The developers are not associated with that release and advise users not to buy it.
You can download the software from our download section, or access project files and documentation via the repositories below.