Search notes:

Registry: HKEY_CURRENT_USER\AppEvents\Schemes\Apps

Turning off most Windows sound

The following simple PowerShell iterates over all sub keys under HKCU\Apps\Schemes\Apps and removes the default values of .Current: 
set-strictMode -version latest

$apps = get-item 'hkcu:\AppEvents\Schemes\Apps'

foreach ($appName in $apps.GetSubKeyNames()) {

   $appName

   $app = $apps.OpenSubKey($appName)

   foreach ($eventName in $app.GetSubKeyNames()) {

      $event = $app.OpenSubKey($eventName)

      $current = $event.OpenSubKey('.Current', $true) # Open with $true for write access
      $default = $event.OpenSubKey('.Default'       )

      if ($current) { $currentVal = $current.GetValue('') } else { $currentVal = '' }
      if ($default) { $defaultVal = $default.GetValue('') } else { $defaultVal = '' }

      "   {0,-30} {1,-60} {2,-60}" -f $eventName, $currentVal, $defaultVal

      if ($currentVal) {
         $current.DeleteValue('')
      }
   }
}
Github repository about-Windows-Registry, path: /HKEY_CURRENT_USER/AppEvents/Schemes/Apps/default-and-current-sounds.ps1

sound.bat

@echo off

rem Turn off most sounds.
rem
rem Verify with c:\windows\system32\MMSYS.CPL

reg add "HKEY_CURRENT_USER\AppEvents\Schemes"                                             /t REG_SZ /d ".None"  /f

rem
rem Pressing tab in cmd.exe when no completion is possible,
rem Default value: C:\Windows\media\Windows Exclamation.wav (Compare with .Default\SystemExclamation)
rem 
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\.Default\.Current"             /t REG_SZ /d ""       /f

reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\AppGPFault\.Current"           /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\Close\.Current"                /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\CriticalBatteryAlarm\.Current" /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\DeviceConnect\.Current"        /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\DeviceDisconnect\.Current"     /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\DeviceFail\.Current"           /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\FaxBeep\.Current"              /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\LowBatteryAlarm\.Current"      /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\MailBeep\.Current"             /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\Maximize\.Current"             /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\MenuCommand\.Current"          /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\MenuPopup\.Current"            /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\Minimize\.Current"             /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\Open\.Current"                 /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\PrintComplete\.Current"        /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\RestoreDown\.Current"          /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\RestoreUp\.Current"            /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\SystemAsterisk\.Current"       /t REG_SZ /d ""       /f

rem
rem Trying to open inexisting registry key in regedit etc.
rem Default value: C:\Windows\media\Windows Exclamation.wav (Compare with .Default\.Default)
rem
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\SystemExclamation\.Current"    /t REG_SZ /d ""       /f

reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\SystemExit\.Current"           /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\SystemHand\.Current"           /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\SystemNotification\.Current"   /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\SystemQuestion\.Current"       /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\WindowsLogoff\.Current"        /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\WindowsLogon\.Current"         /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default\WindowsUAC\.Current"           /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\Explorer\BlockedPopup\.current"         /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\Explorer\EmptyRecycleBin\.Current"      /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\Explorer\FaxError\.current"             /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\Explorer\FaxLineRings\.current"         /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\Explorer\FaxSent\.current"              /t REG_SZ /d ""       /f
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\Explorer\FeedDiscovered\.current"       /t REG_SZ /d ""       /f

rem Another file or directory is clicked in explorer:
reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\Explorer\Navigating\.Current"           /t REG_SZ /d ""       /f

reg add "HKEY_CURRENT_USER\AppEvents\Schemes\Apps\Explorer\SecurityBand\.current"         /t REG_SZ /d ""       /f
Github repository Configure-Windows, path: /sound.bat

TODO

What is the relationship of the *.wav files beneath the .Default key to HKEY_CURRENT_USER\Control Panel\Sound and mmsys.cpl?

See also

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