18.4.1.1 The FFT Dialog Box


FFT fft1.png

Contents

Common Controls

Dialog Theme See Dialog Themes.
Recalculate

See Recalculating Analysis Results.

Input tab

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.

Options tab

Sampling Interval

Specifies the sampling interval. The default is <Auto>, which corresponds to an automatically-computed interval. Please see the algorithm section for details.

Window

Specifies the type of window used to suppress frequency leakage.

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

For more information, see Algorithms, FFT

Window Correction

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

  • None: No correction is applied.
  • Amplitude: Amplitude Correction is applied. It is 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)}}
Normalize Re, Im, and Mag

Specifies whether to normalize the complex, real, imaginary, magnitude, and square magnitude output. The default is false. Note that other outputs such as amplitude are not affected by this variable. Please see the algorithm section for details.

Shift

Specifies whether the result should be rearranged so that the lower frequency components are in the center.

Unwrap phase

Specifies whether the phase should be unwrapped.

Factor

Specifies 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 on page 503 of Numerical Recipes in C, 2nd edition.
Spectrum Type

Specifies the Nyquist interval over which power is calculated.

  • <auto>: If the input signal is real, one-sided power will be chosen; otherwise, two-sided power will be selected. When this option is selected, Origin will look at the input data to determine whether it is complex or not. If the input data is stored in a column of the Complex data type, but the data contains only a real part, Origin will regard it as real, and not as complex, resulting in a one-sided spectrum. Alternately, if the input data has an all-zero column as the imaginary part, Origin will also regard the input as real, and produce a one-sided spectrum.
  • One-sided: One-sided power will be computed.
  • Two-sided: Two-sided power will be computed.
Normalize power to

Specifies the power density normalization method. Please see the algorithm section for details.

  • MSA-Mean Square Amplitude: Mean square amplitude method.
  • SSA-Sum Square Amplitude: Sum square amplitude method.
  • TISA-Time Interval Square Amplitude': Time Integral square amplitude method.
Preview

Specifies the preview content in the dialog.
None, Amplitude/Phase, Power/Phase, Amplitude, Imaginary, Magnitude, Phase, Power, Real, Real/Imaginary, dB, Normalized dB, RMS Amplitude, Square Amplitude , Square Magnitude

Quantities and Plots tab

Select check boxes to create output of the following components of the FFT results:
Real, Imag, Amplitude/Phase, Phase, Power/Phase, Real/Imag, Magnitude, Amplitude, Power, dB, Normalized dB, RMS Amplitude, Square Amplitude, Square Magnitude.

Output tab

See Output Results.

Result Data Sheet

Specifies the worksheet sheet for outputting the result data.

Result Graph Sheet

Specifies the sheet for outputting the result graphs.