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General Questions About Equalizer APO
What is Equalizer APO and how does it work? ⌄
Equalizer APO is a free, open-source audio equalizer for Windows that operates at the system level rather than inside individual applications. The name stands for Audio Processing Object — a specific Windows component type that plugs directly into the operating system's audio rendering pipeline. Once installed, every sound your PC produces passes through the equalizer before reaching your speakers or headphones, regardless of which application generated that audio. This system-wide approach is what separates it from player-specific equalizers and makes it so genuinely useful for consistent processing across your entire computer.
Is Equalizer APO really free, or is there a paid version? ⌄
Completely and permanently free. Equalizer APO is licensed under the GNU General Public License version 2.0, which guarantees your right to use, copy, modify, and distribute it at no cost. There's no paid tier, no premium unlock, no advertising, and no subscription. The project has been free since its first release and the GPL licence ensures it stays that way. The source code is publicly available for anyone to inspect or contribute to.
Who developed Equalizer APO? ⌄
The project was created by Jonas Thedering, who has been the primary developer throughout its history. Over the years, community contributors have added translations, reported and fixed bugs, and improved compatibility with new hardware and Windows versions. The French and Simplified Chinese translations in version 1.4.2, for example, came from community members. The equalizerapo project is a genuine community effort with a clear lead developer steering the architecture.
What's the difference between the equalizer and Peace? ⌄
Equalizer APO is the audio engine — the component that actually processes sound inside the Windows audio service. It's configured through text files and a graphical Configuration Editor. Peace is a separate third-party application that provides a more conventional GUI on top of the equalizer — adding EQ sliders, a live frequency graph, preset management, hotkeys, effects like crossfeed and upmix, and the AutoEQ headphone database. You need the apo equalizer installed before Peace will work, since Peace only controls the configuration — it doesn't process any audio itself. Learn more on the
Peace Equalizer page.
What Windows versions are supported? ⌄
Equalizer APO supports Windows Vista, 7, 8, 8.1, 10, and 11 on x64 and x86 architectures. Version 1.4.2 added ARM64 support for Windows 10 and 11 on ARM devices. Windows 11 is fully supported and version 1.4.2 specifically addresses several Bluetooth and compatibility issues that appeared on newer Windows 11 builds.
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Equalizer APO Installation Questions
Which installer should I download — x64, x86, or ARM64? ⌄
Download x64 if you're on any modern Windows PC with an Intel or AMD processor — which covers the vast majority of users. Download ARM64 only if your device uses an ARM processor (Surface Pro X, Snapdragon-equipped laptops, and similar hardware running Windows 10 or 11). Download x86 only if you're running a 32-bit edition of Windows. Unsure? Press Win + Pause Break or go to Settings → System → About and look at the System type line.
Why do I need to reboot after installing? ⌄
Windows Audio Processing Objects are loaded by the Windows audio service when it starts, which happens at boot. Until you restart, the equalizer apo files are installed on disk but the audio service hasn't loaded them into its processing chain yet. A reboot is required — there's no way to force the audio service to reload its APO list without a restart. This is a Windows architecture constraint, not a quirk of the installer.
I forgot to select a device during installation. What now? ⌄
No problem at all. Open the Start Menu, search for "Equalizer APO Configurator," and launch it. It shows the same device list as during installation. Check the box next to the device you want to process, click OK, and restart your computer. You don't need to reinstall anything.
Does the installer bundle any third-party software? ⌄
No. The installers contain only Equalizer APO itself — no bundled toolbars, browser extensions, or third-party software of any kind. Always download from the
download page to ensure you're getting the clean, original installer.
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Using Equalizer APO — Configuration Questions
Where are the configuration files stored? ⌄
By default, configuration files are stored at C:\Program Files\EqualizerAPO\config\. The main file is config.txt. You can create additional text files in the same folder and reference them using Include commands in config.txt. All files are plain text and can be edited in Notepad or any other text editor.
How do I reset to default settings? ⌄
Open C:\Program Files\EqualizerAPO\config\config.txt in Notepad and delete all the content. Leaving it empty means no processing at all — completely transparent audio. Or paste back the default content from the example.txt file in the same folder. In the Configuration Editor, deleting all modules from the filter chain accomplishes the same thing visually. Changes take effect the moment you save the file.
What is preamplification and should I use it? ⌄
Preamplification is a gain adjustment applied to the entire signal before any other filters. The main reason to use a negative preamplification value is headroom — if you're applying significant EQ boosts, the boosted signal can clip (distort) if the total level exceeds digital maximum. A negative preamp of around -6 dB gives comfortable headroom for 6 dB of boost elsewhere. A positive value simply makes everything louder. Many people use the equalizer apo specifically for microphone amplification by setting a positive preamp on their mic input device while leaving the output chain unchanged.
Can I use the equalizer for PC with a microphone? ⌄
Yes. During installation, check your microphone in the Configurator device list the same way you'd check a playback device. Once active, you can apply any filter to your microphone input — EQ corrections, preamplification for quiet mics, notch filters for hum removal, or even VST processing for compression or de-essing.
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Compatibility Questions
Will it work with my USB DAC or external sound card? ⌄
It depends on the driver. Most USB DACs and sound cards using standard Windows audio drivers (WDM/WASAPI shared mode) work perfectly. Devices that only offer ASIO drivers won't work in ASIO mode because ASIO bypasses the Windows effect chain. If your device also supports WASAPI shared mode — which most consumer-oriented DACs do — that mode works fine with the apo equalizer.
Does Equalizer APO work with Bluetooth headphones? ⌄
Yes. Standard Bluetooth audio (A2DP) routes through the Windows audio stack and is processed by the equalizer. Version 1.4.2 specifically fixed issues with the GraphicEQ and Convolution filters on Bluetooth devices running Windows 11, so if Bluetooth processing wasn't working before, upgrading usually resolves it.
Does it affect game audio and streaming applications? ⌄
Yes. Games and streaming software like OBS use standard Windows audio in shared mode by default. The equalizer for PC processes everything going through the Windows audio stack — game output, Discord voice, OBS monitoring, browser audio — consistently and simultaneously. The near-zero latency means there's no perceptible delay added to game audio or voice communication.
Can I use VST plugins with the equalizer? ⌄
Yes. Equalizer APO supports VST 2.x plugins in both 32-bit and 64-bit formats. Add a VST Plugin module in the Configuration Editor, point it to the DLL file, and the plugin processes audio in the chain. Note that VST3 format is not currently supported — only the original VST2 DLL format works. VST plugins run inside the Windows audio service, which has restricted file permissions, so ensure the DLL is in a readable folder.
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Equalizer APO Troubleshooting
The equalizer isn't doing anything — no effect on audio at all. ⌄
Three causes cover almost all cases. First, check you rebooted after installation — the equalizer can't activate until the audio service restarts. Second, open the Configurator from the Start Menu and verify your audio device has a checkmark. Third, confirm the Configuration Editor shows an active filter chain with the power button in the on state. Work through these three in order before concluding something more serious is wrong.
The equalizer stopped working after a Windows update. ⌄
Windows updates can reset audio driver configurations and dislodge the APO registration. Standard fix: open Equalizer APO Configurator from the Start Menu, uncheck your audio device, click OK, then re-check it, click OK again, and restart your computer. This re-registers the APO with the refreshed driver stack. If that doesn't work, try the Troubleshooting options inside the Configurator and experiment with the "Install as" dropdown (SFX/EFX, SFX/MFX, or LFX/GFX).
The Configuration Editor crashes immediately when I open it. ⌄
This typically affects CPUs without AVX support on versions before 1.4.2. The FFTW library fails to load and causes a crash on startup. Upgrade to version 1.4.2 from the
download page — your configuration files are preserved through a reinstall. If you're already on 1.4.2, try running the editor as administrator (right-click → Run as administrator) to rule out permission issues.
Peace shows my EQ settings but they're not affecting the audio. ⌄
When Peace displays settings but nothing changes in the audio, the problem is almost always in the underlying equalizer installation, not in Peace itself. Peace only writes to the config file — the actual processing comes from the apo equalizer in the Windows audio service. Verify the apo is still active by checking the Configurator and confirming the correct device is selected. Re-registering it through the Configurator and rebooting usually restores everything.
More on Equalizer APO — Extended Answers
A recurring question that doesn't fit neatly into the categories above is about the relationship between the equalizer and Windows Sonic or Dolby Atmos spatial audio. When you enable Windows Sonic for Headphones, it inserts itself into the same processing chain the equalizer uses. The two can coexist, but the order matters — the equalizer processes the signal first, then spatial audio is applied on top, or vice versa. Many users disable Windows Sonic and use Peace's upmix and crossfeed features instead, since the equalizer apo peace combination gives more granular control over the exact processing applied.
Another common question is whether the equalizer affects system sounds — Windows notification sounds, error beeps, and so on. Yes, it does. Everything going through the Windows audio stack is processed, including system sounds. If you apply a dramatic bass boost, your notification sounds will be bassier too. Most people don't find this a problem in practice, but it's worth knowing.
The question of how many filters you can use is technically "unlimited," but practically bounded by the point where CPU load becomes measurable or phase response becomes audible. Dozens of filters are fine on any modern CPU. Hundreds of filters stacked manually is possible but inefficient — if you need that level of precision, the Convolution filter module with an impulse response file is more appropriate and achieves far more detail at lower CPU overhead.
For users interested in the technical side: the equalizer internally converts IIR filter specifications to biquad coefficients evaluated sample-by-sample using SIMD routines. The Convolution filter uses FFTW for frequency-domain processing, efficient even for long impulse responses. VST processing slots in between IIR and convolution stages as configured by the user. The result is a flexible, low-overhead pipeline that rivals commercial products costing hundreds of dollars — a remarkable achievement for a free, community-maintained project.