Fast Fourier Transform (FFT)
A discrete Fourier transform (DFT) converts a signal in the time domain into its counterpart in frequency domain. Let (x i ) be a quence of length N, then its DFT is the quence (F n ) given by
A fast Fourier transform (FFT) is an efficient way to compute the DFT. By using FFT instead of DFT, the
computational complexity can be reduced from O(n 2) to O(n log n ). Note that the input signal of the FFT in Origin can be complex and of any size.
The result of the FFT contains the frequency data and the complex transformed result. Meanwhile, it can also provide the magnitude, amplitude, pha, power density and other computation results. The power density estimation can be made by three different methods: MSA, SSA and TISA. Furthermore, both two-sided and one-sided powers can be computed.
When the FFT is ud, attention should be paid to leakage, which is caud by the FFT's assumption that the input signal repeats periodically and that the periodic length is equal to the length of the actual input. However, if the true signal is not periodic or if the assumed periodic length is not correct, leakage will occur. This will cau both the amplitude and position of a frequency measurement to be i
naccurate. (Plea e the figure below.) Origin supports the u of window functions to mitigate leakage. Several window functions are supported, including Triangular, Bartlett, Welch, Hann, Hamming and Blackman, each of which has unique advantages and drawbacks. A specific window function should be lected according to the kind of signals being analyzed.
To u FFT:
1.
Make a workbook or a graph active. 2.
Select Analysis: Signal Processing: FFT: FFT from the Origin menu.
페이지 1 / 1Fast Fourier Transform (FFT)
The FFT1 Dialog Box
Input Specifies the input signal, which could be complex. The real and imaginary parts of the signal can be save different columns or in the same column. The default is <Active>, which corresponds to the active datat
Sampling Interval Specifies the sampling interval. The default is <Auto>, which corresponds to an automatically-computed in Plea e the algorithm part for details.
Specifies the computation options.
virustotalWindow
Specifies the type of window ud to suppress frequency leakage.
z Rectangle
Rectangular window:
z Welch
Welch window
z Triangular
Triangular window
z Bartlett
Bartlett window
z Hanning
Hann Window
Options
z Hamming
Hamming window:
z Blackman
Blackman window
Normalize Re, Im and Mag
Specifies whether to normalize the complex, real, imaginary, magnitude and sqaure magnitude output. The default is fal. Note that other outputs such as amplitude are not affected by this variable. Plea e the algorithm ction for details.
Shift
Specifies whether the result should be rearranged so that the lower frequency components are in the center.
Unwrap pha
Specifies whether the pha should be unwrapped.在一起英文
Factor
Specifies whether the Electrical Engineering or Science convention is ud to t the sign of the Exponential Pha factor.
z-1 (Electrical Engineering)
The pha factor sign will be opposite to that of the Science option.
z+1 (Science)
The pha factor will be t according to the formulae listed in page 503 of
Numerical Recipes in C, 2nd edition.
Spectrum Type
Specifies the Nyquist interval over which power is calculated.
z<auto>
If the input signal is real, one-side power will be chon; otherwi, two-side
power will be lected.
z One-sided
One-sided power will be computed.
z Two-sided
Two-sided power will be computed.
Normalize power to
Specifies the power density normalization method. Plea e the algorithm part for detail.
z MSA-Mean Square Amplitude
dlnaMean square amplitude method
z SSA-Sum Square Amplitude
Sum square amplitude method
z TISA-Time Interval Square Amplitude'
Time Integral square amplitude method
Preview Specifies the preview content in the dialog.
z None
NONE
z Amplitude/Pha
Both the amplitude and the pha.
xfh
z Power/Pha
Both the power and the pha.
z Amplitude
The amplitude
z Imaginary
can的过去式The imaginary parts of the transformed data z Magnitude
The magnitude
z Pha
The pha
z Power
The power spectrum or power density
z Real
The real parts of the transformed data
z Real/Imaginary
Both the real parts and imaginary parts of the transformed data z dB
The amplitude in dB
z Normalized dB
The normalized amplitude in dB
z RMS Amplitude
The RMS amplitude
z Square Amplitude
The square amplitude
z Square Magnitude
The square magnitude
U the check boxes in this branch to control whether a quantity should be output and plotted.
z Real
Specifies whether or not to output a graph of the real parts of the FFT result.
z Imag
pierceSpecifies whether or not to output a graph of the imaginary parts of the FFT result.
z Amplitude/Pha
Specifies whether or not to output a combined graph of amplitude and pha.
z Pha
Specifies whether or not to output a graph of the pha.
z Power/Pha
最好的在线翻译
Specifies whether or not to output a graph of the pha.
Plot z Real/Imag
Specifies whether or not to output a combined graph of power and pha. z Magnitude
Specifies whether or not to output a graph of the magnitude.
z Amplitude
Specifies whether or not to output a graph of the amplitude.gola
z Power
Specify whether or not to output a graph of the power.
z dB
Specifies whether or not to output a graph of the result of dB.
z Normalized dB
Specifies whether or not to output a graph of the result of normalized dB. z RMS Amplitude
Specifies whether or not to output a graph of the RMS amplitude.
z Square Amplitude
Specifies whether or not to output a graph of the squared amplitude.
z Square Magnitude
Specifies whether or not to output a graph of the squared magnitude.
Result
Data
Sheet
Specifies the worksheet sheet for outputting the result data.
megging
Result
Graph
Sheet
Specifies the sheet for outputting the result graphs.
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