18.4.2.1 The IFFT Dialog Box

IFFT ifft1.png
Dialog Theme See Dialog Themes.
Recalculate

See Recalculating Analysis Results.

Input

Specifies the input signal, which could be complex. The real and imaginary parts of the signal can be saved in different columns or in the same column. The default is <Active>, which corresponds to the active dataset.

See Specifying Your Input Data.

Sampling Interval

Specifies the sampling interval. The default is <Auto>, which corresponds to an automatically-computed interval. Please see the Automatic Computation of Sampling Interval section of the FFT Algorithms page for details.

Plot

Specifies what will be plotted in the preview window and outputted to the result graph sheet.

  • None
  • Amplitude/Phase
  • Real
  • Imaginary
  • Amplitude
Options

Specifies the computation options.

Undo Shift Input Data: Specifies whether the input is generated by a FFT with the results shifted. If this option is checked, the input data points will first be swapped in order to undo the effect of shifting. Window: Specifies the type of window to be used for suppressing the leakage.

  • Rectangle:
  • Welch
  • Triangular
  • Bartlett
  • Hanning
  • Hamming
  • Blackman
  • Gaussian
  • Kaiser

For more information on the window type, see the Algorithms page.

Window Correction: The Window Correction Factor used to correct the alteration made by applying a window to the input data.

  • None
  • Amplitude: Used when the true amplitude of narrow band data is required. The Amplitude Correction Factor is defined as
ACF=\frac{1}{mean(w[n])}
  • Power: Energy Correction is applied. It is used when the true energy level of the data is required. The Power Correction Factor is defined as
ECF=\sqrt{\frac {1}{mean(w[n]^2)}}

Factor: Determines whether the Electrical Engineering or Science convention is used to set the sign of the Exponential Phase factor.

  • -1 (Electrical Engineering): The phase factor sign will be opposite to that of the Science option.
  • +1 (Science): The phase factor will be set according to the formulae listed in page 503 of Numerical Recipes in C, 2nd edition.

Unwrap phase: Determines whether the phase should be unwrapped. If unwrapped, phase data will be defined in the range of 180° to +180°.

Result Data Sheet

Specifies the worksheet for outputting result data. See Output Results.

Result Graph Sheet

Specifies the worksheet for outputting result graphs. See Output Results.

Notes: If the Spectrum Type is selected <auto> option when performing FFT, please pay attention to how Origin looks in the data to determine whether it is complex or not, so to make sure whether the signal can be restored by using inverse fast Fourier transform.