PushToOpen

Voice-activated push-to-talk for Windows. Your microphone level crosses a threshold → PushToOpen virtually holds a key you've bound. You go quiet → it releases. Threshold, key, timing, input device, monitor, noise suppression, window-restriction, theme — all configurable from a clean WinUI 3 desktop app.

Highlights

Core

• Real-time RMS + peak metering with a smoothed gradient VU bar + moving threshold line
• Threshold state machine with attack, release, and debounce windows
• Reliable Windows SendInput-based key simulation (scan codes + extended-key handling); keyboard or mouse buttons 1–5
• Settings auto-persist (debounced JSON write to %LocalAppData%\PushToOpen\settings.json)
• Compact floating overlay window with lock-position toggle, smooth pointer-capture drag, live mute icon, dB readout
• System tray with Open / threshold presets / Exit (Command-bound, namescope-safe)
• Optional launch on Windows startup (per-user HKCU\…\Run)
• Device hot-swap: disconnect/reconnect the mic and PushToOpen rebinds automatically
• Fail-safe: any unexpected exit, device loss, or close releases the virtual key

Audio

• Hear yourself — pipe your mic to your default output for monitoring (with its own gain). Use headphones.
• Voice noise suppression — pure C# FFT-based spectral subtraction. Hand-rolled Cooley-Tukey, periodic-Hann analysis at 50% hop (COLA), per-bin noise floor learned during low-energy frames, oversubtraction with smoothed Wiener gain. Cleans steady-state hiss + fan noise from the threshold detection and monitor path. (Other apps still see your raw mic — see honest limits below.)
• Input gain trim + noise gate floor

Hotkeys

• Push-to-talk binding (keyboard or mouse, default V)
• Mute toggle global hotkey — separate key flips Mute on/off from any focused window
• Both bind via in-app capture (Esc cancels)

Window restriction

• "Window" tab — pick an open app. PushToOpen only fires while that process owns the foreground window. Tab to anything else → gate stays closed, no key. Auto-resumes when you focus it again.

Themes

• Six built-in palettes — Indigo Night, Phosphor, Crimson, Aurora, Sunset, Mono
• Custom PNG/JPG background image with adjustable opacity (translucent watermark — unpackaged WinUI 3 can't do real backdrop blur)
• Layout modes: full Sidebar or Compact (icon-only nav rail)

Honest limits

PushToOpen is a key simulator, not a virtual audio device. It reads your microphone to decide whether to press a key — it doesn't replace what Discord, Teams, Zoom, etc. capture. That means:

• The noise-suppression toggle improves threshold accuracy (no false triggers from fan noise) + the Hear-yourself monitor playback. It does not clean up the mic stream other apps record.
• For system-wide neural noise suppression (Krisp-grade), use Discord's built-in Krisp toggle (Voice Settings → Noise Suppression → Krisp), NVIDIA Broadcast, or a virtual cable + VoiceMeeter.

Requirements

• Windows 10 build 19041+ or Windows 11, x64
• Self-contained published binaries need no .NET install
• Building from source: .NET 8 SDK

Run prebuilt (casual users)

The dist/ folder in the repo holds a ready-to-run self-contained build:

dist/
├── Start PushToOpen.lnk         ← double-click this
├── Install Desktop Shortcut.bat ← optional: adds a Desktop shortcut
├── README.txt
└── PushToOpen/                  ← program + DLLs (don't touch)

Zip the whole dist/ folder to share. Recipient unzips anywhere, double-clicks Start PushToOpen.lnk. No installer, no admin, no runtime download.

Build from source

From the repo root:

dotnet restore
dotnet msbuild .\src\PushToOpen\PushToOpen.csproj -p:Configuration=Release -p:Platform=x64

Or open PushToOpen.sln in Visual Studio 2022 (17.8+) and press F5. Platform must be x64 — WindowsAppSDK self-contained mode rejects AnyCPU.

Single-folder self-contained publish:

dotnet publish .\src\PushToOpen\PushToOpen.csproj `
    -c Release -p:Platform=x64 `
    -p:WindowsAppSDKSelfContained=true `
    -p:SelfContained=true `
    --runtime win-x64 `
    --output .\dist\PushToOpen

Both <SelfContained>true</SelfContained> and <WindowsAppSDKSelfContained>true</WindowsAppSDKSelfContained> are required — the second bundles the WinAppSDK native DLLs alongside the .NET runtime.

First-run tips

1. Open the app.
2. Audio tab → pick your microphone.
3. Hotkey tab → bind the key PushToOpen should hold while you talk (default V).
4. Live tab → speak. Drag Threshold so the gate opens when you talk and closes when you're silent.
5. (Optional) Hear yourself under Audio to verify what the noise suppressor is doing. Headphones.
6. (Optional) Window tab → pin PushToOpen to one app so it doesn't fire while you type in other windows.
7. (Optional) Themes tab → pick a palette + background image + layout.

Architecture

src/PushToOpen/
├── App.xaml(.cs)                   – DI bootstrap, theme apply, lifecycle, overlay mgmt, global hotkey wiring
├── Program.cs                      – STA entry point
├── MainWindow.xaml(.cs)            – Shell, tray icon (Command-bound), status bar
├── Views/
│   ├── MainShellView.xaml(.cs)     – Sidebar / content / status, layout-mode switching, theme bg image
│   ├── OverlayView.xaml(.cs)       – Compact pod with lock toggle + mute icon
│   └── OverlayWindow.xaml(.cs)     – Borderless window + pointer-capture drag
├── Controls/VuMeter.cs             – Custom level + threshold + active-glow control
├── Styles/                         – Color brushes + control templates (live-mutated by ThemeService)
├── Models/
│   ├── AppSettings                 – Persistent state for everything below
│   ├── AudioDeviceInfo, KeyBindingInfo, WindowInfo
│   └── ThemeDefinition             – Palette + accent gradient stops
└── Services/
    ├── SettingsService             – Debounced atomic JSON persistence (tmp → rename)
    ├── AudioCaptureService         – WASAPI capture, RMS / peak, device hot-swap, monitor, NS pipeline
    ├── NoiseSuppressor             – Hand-rolled FFT + spectral subtraction
    ├── ThresholdEngine             – Attack / release / debounce / mute / app-gate state machine
    ├── InputSimulator              – SendInput key down/up (down stays true on failure → retries)
    ├── HotkeyCaptureService        – Low-level kbd + mouse hook for binding capture
    ├── GlobalHotkeyListener        – Always-on hook listening for the mute-toggle binding
    ├── ForegroundWatcher           – Polls GetForegroundWindow every 250ms
    ├── WindowEnumerator            – EnumWindows + DWM-cloak / tool-window filtering
    ├── ThemeService                – Six palettes, live brush.Color mutation
    ├── StartupService              – HKCU Run key registration
    └── PushToTalkCoordinator       – Wires audio → engine → input + foreground → app-gate + settings → everything

Data flow

WASAPI capture ─► AudioCaptureService ─► [optional NS] ─► ThresholdEngine ─► InputSimulator
                          │                                       │
                          ▼                                       ▼
                  ViewModels                              Tray / Overlay UI

GetForegroundWindow (250ms poll) ─► ForegroundWatcher ─► Coordinator.ApplyAppGate
                                                              │
                                                              ▼
                                                       ThresholdEngine.SetAppGate

Low-level hook (mute-toggle key) ─► GlobalHotkeyListener ─► Task.Run ─► Settings.Mutate(Muted = !Muted)

Reliability invariants

1. Never leak a held key. PushToTalkCoordinator subscribes to AppDomain.ProcessExit and UnhandledException and releases the simulator before exit. InputSimulator.Dispose() also releases. OnTrayExit releases + force-terminates.
2. Audio thread isolation. WASAPI OnDataAvailable reads shared doubles under _gate lock; UI updates marshal via DispatcherHelper. Noise suppressor processes in-place on the callback thread (cheap STFT, ~few % of one core).
3. Device hot-swap. AudioCaptureService registers IMMNotificationClient; device add/remove/default-change triggers Task.Run(RefreshDevicesAsync) (off the COM callback thread).
4. Hook-thread safety. Low-level keyboard hook callbacks (mute-toggle handler) bounce off the hook thread via Task.Run before doing settings mutation — keeps callbacks well under LowLevelHooksTimeout.

Settings file

%LocalAppData%\PushToOpen\settings.json — atomic write (tmp → rename) with ~400 ms debounce. Delete to reset.

License

MIT.