Everything Atout APO does, section by section.
Covers version 1.0.20. Looking for quick answers instead? Check the FAQ.
Getting started
Atout APO is a real-time EQ, Dynamic EQ, and Compressor application that applies directly to your Windows system audio. The first time you launch it after installing, an internet connection is required to start a 7-day free trial. If you already have a key, enter it on that screen — or click Buy to purchase. During the trial a banner at the top of the main screen shows remaining days (rounded up; the last 24 hours show Last day), with Buy and Enter License Key. After the trial ends, processing returns to factory defaults until you activate a license key — so you can hear why the sound changed. The real-time spectrum still works so you can confirm the app is connected.
Install & first launch
Run the downloaded installer and follow the prompts to complete installation.
Once installed, the app launches automatically and shows the license entry screen.
If you already have a key, enter it and click Activate. You can also click Buy on that screen. If you do not have a key, the 7-day trial starts automatically when you are online. If you are offline on first launch, the trial does not start and the app asks you to connect to the internet.
After a trial starts or a license activates, the main screen opens. A paid license stays on this computer — you will not need to enter the key again on later launches.
Main screen overview
The main screen has Stereo Field at the very top, the EQ graph below it, and four panels along the bottom: Preset, Dynamic EQ, Compressor, and Master.
| Area | What it does |
|---|---|
| Stereo Field | Live left–right image of the sound currently playing |
| EQ graph | The main equalizer — shape tone across up to 8 bands, with a live spectrum overlay |
| Preset panel | Save and load your settings by name |
| Dynamic EQ | Sub (low end) and Air (high end) — two bands that duck automatically, with their own live spectrum |
| Compressor | Compresses sound above a set threshold to control dynamic range |
| Master | Final output volume, plus Global Bypass for all effects |
EQ (parametric equalizer)
EQ lets you shape tone across up to 8 bands, each set as a Cut, Peak, or Shelf-type filter. Double-click the 0dB line on the graph to add a new band.
Adding & editing bands
- Double-click the 0dB line on the graph to add a new band (up to 8 total).
- Click a band point to open its edit panel, where you can set Hz, dB, Q, and Shape precisely.
- Click the headphone icon to Audition just that band in isolation and dial in the exact spot (Peak bands only).
Shape — 5 filter types
| Shape | Description |
|---|---|
| Low-Cut | High-pass filter that removes everything below the set frequency |
| Low Shelf | Raises or lowers the entire range below the set frequency |
| Peak | Raises or lowers a bell-shaped range centered on the set frequency (the most common EQ type) |
| High Shelf | Raises or lowers the entire range above the set frequency |
| High-Cut | Low-pass filter that removes everything above the set frequency |
Parameter ranges
| Parameter | Range | Description |
|---|---|---|
| Hz | 20 – 20,000 | The band's center (or corner) frequency |
| dB | -24 – +24 | Gain at that frequency — positive boosts, negative cuts |
| Q | 0.5 – 20 | Band width — higher values are narrower and sharper |
| Slope | 6 / 24 / 42 / 60 / 78 / 96 dB/oct | Rolloff steepness, shown only for Low-Cut / High-Cut |
Dynamic EQ
Dynamic EQ only reacts once the signal level crosses a set Threshold. You can configure two bands independently: Sub (low end) and Air (high end). The panel graph shows a live spectrum of the same audio as the EQ view, with Sub and Air ranges highlighted.
Sub / Air tabs
| Tab | Description |
|---|---|
| SUB | Detects and shapes the low end |
| AIR | Detects and shapes the high end |
Parameter ranges
| Parameter | Range | Description |
|---|---|---|
| Freq (Sub) | 20 – 1,800 Hz | Sub band's center frequency |
| Freq (Air) | 4,500 – 20,000 Hz | Air band's center frequency (100Hz steps) |
| Duck | -50 – 0 dB | How far to pull the level down once the threshold is crossed |
| Threshold | -60 – 0 dB | Only signals above this level trigger a response (drag vertically to adjust) |
Compressor
Automatically pulls down sound louder than a set Threshold to control dynamic range. Found in the Compressor panel at the bottom right of the main screen.
Knobs
| Control | Range | Description |
|---|---|---|
| Ratio | 1:1 – 20:1 | How strongly sound above the threshold is compressed |
| Attack | 0.1 – 500 ms | Time before compression kicks in — shorter reacts faster |
| Release | 10 – 2,000 ms | Time for compression to release — longer returns to level more gradually |
Meters (3 vertical bars)
| Meter | Description |
|---|---|
| Thresh | Sound above this point starts being compressed. Drag vertically to adjust, -60 to 0dB |
| GR | Shows how much gain reduction is happening in real time |
| Out | Shows output level, and doubles as a control — drag vertically to adjust makeup gain (-24 to +24dB) |
Master
Controls the volume of the final output after all effects, and lets you bypass everything at once if needed.
| Control | Description |
|---|---|
| Master fader | Adjusts final output volume from -60 to +36dB |
| Global Bypass | Bypasses EQ, Dynamic EQ, Compressor, and all other effects, outputting the unprocessed (dry) signal. The button's border is highlighted in red while active. |
Stereo Field
Shows where the sound currently playing is coming from — left, right, or somewhere in between — updated live as you listen. When several sounds play at once, each one shows up as its own cluster of dots at its own position along the bar.
| Element | Description |
|---|---|
| L – R bar | The horizontal line from Left to Right; where the dots sit along it shows the current stereo position |
| Dot cluster | A live snapshot of where sound is landing — a wider spread means a wider stereo image, and separate clusters mean separate sounds coming from different positions at once |
Presets
Save your current EQ, Dynamic EQ, Compressor, and Master settings under a name, and load them again later.
| Feature | Description |
|---|---|
| Load | Selecting a saved preset from the dropdown applies its EQ, Dynamic EQ, Compressor, and Master settings together |
| Save | Saves your current EQ, Dynamic EQ, Compressor, and Master settings as a new named preset |
| Folder icon | Opens the folder where preset files are stored, directly in File Explorer |
Per-section presets
Alongside the full preset above, the EQ, Dynamic EQ, and Compressor panels each have their own save button (disk icon) in their header, so you can save just that panel's settings on its own.
| Panel | Filename prefix |
|---|---|
| EQ | EQ_ |
| Dynamic EQ | DEQ_ |
| Compressor | COMP_ |
The prefix is added automatically when you save — you only need to type the name itself.
To load a section preset, click the EQ, DEQ, or COMP button at the bottom of the Preset panel to open a dropdown listing that section's saved presets.
Settings menu & bottom icons
Click the gear icon at the bottom of the screen to expand additional settings — language, tooltip visibility, the user guide, and more.
| Icon | Function |
|---|---|
| Circular arrow | Resets EQ, Dynamic EQ, Compressor, and Master to their defaults |
| Document | Opens the online user guide in your browser |
| Question mark | Toggles the hover tooltips that appear over knobs and buttons |
| Globe | Changes the app's UI language (9 languages total, including English and Korean) |
| Gear (Settings) | Expands or collapses the settings items below it |
Reset to Default
Use this when you've been adjusting EQ, Dynamic EQ, Compressor, and Master settings and want to return everything to its original state. Click the circular arrow icon at the top of the settings icon list to run it.
| Item | Description |
|---|---|
| What gets reset | EQ (4 bands, Peak, 50/200/1k/5k Hz, 0dB) · Dynamic EQ (Sub 200 Hz / Air 5 kHz, Duck 0 dB, Threshold 0 dB) · Compressor (4:1, 0.1ms, 300ms) · Master (0 dB) · Global Bypass OFF. |
| What doesn't get reset | Language setting, tooltip visibility, license activation status, saved preset file list |
License & device change (Reset Device)
A single license key can only be used on one computer. If you replace your computer or do a fresh Windows install, you can change device registration yourself using the method below.
When you change devices
Launching the app on a new (or freshly reformatted) computer shows the license activation screen. Entering your existing key and clicking Activate may show an "activation limit" error, since it's already registered to another device. When this happens, a Reset Device button appears alongside it along with a purchase email field — enter the email address used at purchase, then click Reset Device to deregister the previous device and automatically re-register this computer.