C / C++ / MFC

• Depending on the FFT algorithm you're using, the output can be either in the range [-f_s,f_s) or [0,2f_s), that is, the component for DC (0 Hz) can be placed at the beginning of the resulting sequence or in the middle point. You can apply the following identity to convert between these two representations:

  X(f)=X(f+2f<sub>s</sub>),

  that is, you can think of the frequency axis of the FFT as periodically repeating the interval [-f_s,f_s).
  
• There's a signal theory artifact called aliasing by which components of frequencies higher than f_s appear at lower frequencies when computing the FFT. To avoid this, you have to pre-filter your image to a cutoff frequency of f_s. On a first approach you might ignore this step and obtain good results if the signal is known to not have significant power for frequency beyond f_s, as it happens for voice signals.
  

E<sub>X</sub>(f) = |X(f)|<sup>2</sup> + |X(-f)|<sup>2</sup>

• linear: points in the x-axis are evenly spaced (with respect to frequency).
  
• logarithmic: points in the x-axis are not evenly spaced (like 10 Hz, 20, Hz, 30, HZ, etc.) but on an exponential fashion: for instance, 10¹ Hz, 10²=100 Hz, 10³=1000 Hz, etc.
  

Total = sqrt(Right<sup>2</sup>+Left<sup>2</sup>).

BOOL CMyWinApp::InitInstance()<br />
{<br />
...<br />
// Parse command line for standard shell commands, DDE, file open<br />
   CCommandLineInfo cmdInfo;<br />
   ParseCommandLine(cmdInfo);<br />
// DON'T display a new MDI child window during startup!!!<br />
   cmdInfo.m_nShellCommand = CCommandLineInfo::FileNothing;<br />
// Dispatch commands specified on the command line<br />
   if (!ProcessShellCommand(cmdInfo))<br />
      return FALSE;<br />
...<br />
};

BOOL CMotionControllerApp::InitInstance()<br />
{<br />
AfxEnableControlContainer();<br />
<br />
// Standard initialization<br />
// If you are not using these features and wish to reduce the size<br />
// of your final executable, you should remove from the following<br />
// the specific initialization routines you do not need.<br />
<br />
#ifdef _AFXDLL<br />
Enable3dControls(); // Call this when using MFC in a shared DLL<br />
#else<br />
Enable3dControlsStatic(); // Call this when linking to MFC statically<br />
#endif<br />
<br />
// Change the registry key under which our settings are stored.<br />
// TODO: You should modify this string to be something appropriate<br />
// such as the name of your company or organization.<br />
SetRegistryKey(_T("Local AppWizard-Generated Applications"));<br />
<br />
LoadStdProfileSettings(); // Load standard INI file options <br />
<br />
// Register the application's document templates. Document templates<br />
// serve as the connection between documents, frame windows and <br />
<br />
CSingleDocTemplate* pDocTemplate;<br />
pDocTemplate = new CSingleDocTemplate(<br />
IDR_MAINFRAME,<br />
RUNTIME_CLASS(CMotionControllerDoc),<br />
RUNTIME_CLASS(CMainFrame), // main SDI frame window<br />
RUNTIME_CLASS(CMotionControllerView));<br />
AddDocTemplate(pDocTemplate);<br />
<br />
// Parse command line for standard shell commands, DDE, file open<br />
CCommandLineInfo cmdInfo;<br />
ParseCommandLine(cmdInfo);<br />
<br />
CSplashWnd::EnableSplashScreen(cmdInfo.m_bShowSplash);<br />
<br />
cmdInfo.m_nShellCommand = CCommandLineInfo::FileNothing;<br />
// Dispatch commands specified on the command line<br />
if (!ProcessShellCommand(cmdInfo))<br />
return FALSE;<br />
<br />
// The one and only window has been initialized, so show and update <br />
// m_pMainWnd->ShowWindow(SW_SHOWMAXIMIZED);<br />
// m_pMainWnd->UpdateWindow();<br />
<br />
return TRUE;<br />
}