Equalizer APO is intended for Windows users who want a single correction profile to affect sound across games, browsers, music players, and other apps. Because it works within the Windows audio engine rather than inside each individual program, it can apply the same headphone or speaker adjustments wherever audio follows the normal Windows playback path. It is also suited to users who tune a room using measurements or want to equalize a microphone across recording applications.
Filters for playback and recording
The filter system supports parametric and graphic equalization. Available filter types include peaking, shelving, high-pass, low-pass, and notch filters, while GraphicEQ can use any number of bands. Settings can be assigned separately to output devices, microphones, and individual channels, including left, right, and LFE. This makes it possible to correct one channel or device without applying identical adjustments everywhere.
For measurement-based work, Equalizer APO can read filter text files exported by Room EQ Wizard. It also supports VST effect plugins and impulse responses, which can be used for room correction or reverb. Installing the APO on a recording device enables microphone equalization for apps that use the normal Windows recording path.
How configuration works
Equalizer APO installs as an Audio Processing Object (APO), a component of the Windows audio engine. During setup, its Device Selector asks which playback and recording devices should receive the APO. Selecting the device actually used for listening or recording is important: if the wrong endpoint is chosen, the filters will not affect the audio you hear or capture. The audio service may need to restart after device selection, or Windows may need to reboot.
Configuration is available through either a plain text file named config.txt or the bundled Configuration Editor. Saving changes to the text file applies them immediately. The editor provides a graphical way to build the same filters and displays the resulting frequency response, though its controls are technical rather than designed as a simple preset-and-slider interface. Users who add a headset or another endpoint later can rerun the Device Selector to include it.
For the APO to affect the chosen Windows device, Equalizer APO must be installed on that device and audio must use the normal Windows audio path. Programs using ASIO or WASAPI exclusive mode bypass that path, so their sound is not processed by the equalizer.
Practical fit and system details
The system-wide approach avoids maintaining separate equalizer settings in every compatible app, but it also makes correct device setup part of the initial configuration. A user troubleshooting missing changes should check that the current output device is selected in Device Selector and restart the audio service when prompted. The same principle applies when installing the APO for microphone processing: the intended recording device must be selected.
Equalizer APO is Windows-only, with x64, x86, and ARM64 builds; the 1.4 series includes those build options. It is developed by Jonas Thedering and is open source under the GNU GPL v2, with no paid edition. Its flexible filters and device-level settings suit users comfortable with technical audio configuration, while users seeking a basic interface with ready-made presets may find the setup and editor less convenient.