Glossary of Basic Terms Relating to FFT Analysis


This is a glossary of basic terms relating to FFT analysis and FFT analyzers. All the descriptions of terms are based on Ono Sokki FFT analyzers. Note that these descriptions may not apply to FFT analyzers from other manufacturers.

Each term is linked to its corresponding definition.


A Aliasing (Aliasing Noise)
Amplitude Probability Density Function
Amplitude Probability Distributions Function
Analysis Data Length
Autocorrelation Function
  • Summation averaging, normalize summation averaging
  • Exponential averaging
  • Peak hold
  • Subtraction averaging
  • Sweep averaging
B Bode Diagram
C Calibration Function (EU Function)
Channel Delay Function
Coherence Blanking Function
Coherence Function
Coherence Output Power
Coincident Quadrature Diagram
Correlation Function
Crest Factor
Cross-Correlation Function
Cross Spectrum
Curve Fitting
D Damping Factor
Decibel (dB)
E Energy Spectrum Density
F Fourier Transform
Frequency-Axis Differential/Integral
Frequency Resolution
Frequency Response Function
G Group Delay
H Harmonic Distortion
Hilbert Transform
I Impulse Response
Inverse Fourier Transform
L Liftered Envelope
M Modal Analysis
N Nichols Diagram
Nyquist Diagram
O Octave Analysis
Open-Loop/Closed-Loop Operation
Overall Value
Overlap Processing
P Phase Spectrum
Power Spectrum
Power Spectrum Density
R Real-time Analysis
Rotational Order Ratio Analysis
Rotational Tracking Analysis
Root Mean Square (RMS)
S Sampling Theorem
Sound Intensity (SI) or Acoustic Intensity (AI)
T Time-Axis Differential/Integral
Time-Axis Waveform
Time Waveform Statistical Calculation
  • Mean value (MEAN)
  • RMS value (RMS)
  • Standard deviation (S.D.)
  • Skewness (SKEWNESS)
  • Kurtosis (KURTOSIS)
  • Crest factor (CRESTFACTOR)
Trigger Function
W Wigner Distribution
Window (Time Window)
Z Zooming Function



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