AGC Guard

A small Windows system-tray utility for ham radio operators: it watches for your transceiver's USB audio codec being plugged in and automatically turns off Windows' built-in audio "enhancements" (which include automatic gain control, noise suppression, loudness equalization, etc.) on both the speaker and microphone side. Those enhancements actively fight the radio's own AGC and can badly distort FT8/SSB/etc. audio, so most digital-mode setups want them permanently off for the transceiver's audio device - this app makes sure they stay off even after a reboot, a driver update, or unplugging/replugging the radio.

What it does

• Runs quietly in the system tray. Left/double-click or the context menu opens the device manager; right-click gives you the full menu.
• You tell it which USB audio device(s) to watch, identified by USB Vendor/Product ID (not by USB port), via a small wizard: "Disconnect the radio → click Next → reconnect the radio" and it auto-detects the new audio endpoint(s) and offers to add them.
• Whenever a watched USB audio device is plugged in (or is already connected at app startup), it disables the "Disable all enhancements" property on that endpoint - for both the render (speaker) and capture (microphone) side if the device exposes both.
• Shows a small non-intrusive balloon/toast notification near the tray icon whenever it actually disables something.
• Lets you enable/disable monitoring, and add/remove watched devices, from the tray menu.
• Can register itself to start with Windows (HKCU Run key - no admin rights required).
• Logs everything (including problems) to %AppData%\Hamstuff\AgcGuard\logs\agcguard-YYYYMMDD.log.

How the "disable enhancements" part actually works

Every Windows audio endpoint (each speaker/microphone the OS knows about) has a property called PKEY_AudioEndpoint_Disable_SysFx. This is exactly the property behind the classic Sound control panel's Enhancements tab → "Disable all enhancements" checkbox, and the modern Settings app's "Enhance audio" toggle. Hamstuff AGC Guard sets that property to 1 (disabled) on the matching endpoint(s).

It does this via the undocumented IPolicyConfig COM interface (the same one the Sound control panel itself uses internally), not the documented IMMDevice::OpenPropertyStore route - that route only grants a non-administrator caller read-only access, and even elevated it targets the wrong registry key for this property (the endpoint's Properties store, not the FxProperties store the setting actually lives in). IPolicyConfig gets both right and needs no elevation, because the write happens inside the Windows Audio service on the caller's behalf.

Limitations:

• This only affects effects implemented through Windows' classic audio effects/APO framework - what the Enhancements tab / "Enhance audio" toggle controls. It does not - and cannot - change anything inside the radio's own hardware DSP.
• Windows 11 also has a separate, newer set of per-effect microphone toggles (Settings → Sound → Input device → Properties → "Noise suppression" / "Echo cancellation" / "Automatic gain control"). These are a different mechanism entirely and are not controlled by this app - there's no confirmed way for a non-elevated app to flip them programmatically. They do persist per-device once set, though (survive unplug/replug), so if your transceiver's mic shows one of these toggled on, turn it off there once by hand and it'll stay off.

Device identification

Each monitored device is stored as a USB VID_xxxx&PID_xxxx pair, extracted from the audio endpoint's underlying PnP device instance ID. That means it matches the type of device regardless of which USB port you plug it into (and regardless of whether Windows assigns it a new endpoint ID after a driver update).

Building

Requires the .NET 8 SDK and Windows (WinForms + the Core Audio COM APIs used here are Windows-only).

dotnet build -c Release

The output executable is HamstuffAgcGuard.exe. No NuGet packages are required - all Windows COM interop is hand-written against the public, documented Core Audio interfaces, so the project builds fully offline.

Using it

1. Launch HamstuffAgcGuard.exe. It appears in the system tray (you may need to expand the hidden icons area the first time).
2. Right-click the tray icon → Manage Devices... → Add via Wizard...
3. Follow the 3-step wizard: disconnect the radio's USB audio interface, click Next, then plug it back in. The wizard detects the new endpoint(s) automatically and lets you pick which one(s) to add.
4. That's it - from now on, whenever that device is connected (including right now, and on every future plug-in or app/Windows restart), its Windows audio enhancements/AGC get switched off automatically, with a quick toast confirming it.
5. Optional: right-click → Start with Windows to have it launch at sign-in automatically.

To stop watching a device, open Manage Devices... and remove it from the list. To pause monitoring entirely without removing your device list, uncheck Monitoring Enabled in the tray menu.

Troubleshooting

Check %AppData%\Hamstuff\AgcGuard\logs\ (also reachable via the tray menu's Open Log Folder) for a dated log file with details on any failures (e.g. a device that disappeared mid-operation, or a property that couldn't be written).