Test and Measurement 161546.3.4.1 FFT Measurements
The Fourier Transform is a mathematical filtering pro-
cess that determines the spectral content of a time
domain signal. The Fast Fourier Transform, or FFT, is a
computationally efficient version of the same. Most
modern measurement systems make use of the com-
puter’s ability to quickly perform the FFT on sampled
data. The cousin to the FFT is the IFFT, or Inverse Fast
Fourier Transform. As one might guess, the IFFT takes
a frequency domain signal as its input and produces a
time domain signal. The FFT and IFFT form the bed-
rock of modern measurement systems. Many fields out-
side of audio use the FFT to analyze time records for
periodic activity, such as utility companies to find peak
usage times or an investment firm to investigate cyclic
stock market behavior. Analyzers that use the Fast Fou-
rier Transform to determine the spectral content of a
time-varying signal are collectively called FFTs. If a
broadband stimulus is used, the FFT can show the spec-
tral response of the device under test (DUT). One such
stimulus is the unit impulse, a signal of theoretically
infinite amplitude and infinitely small time duration.Figure 46-14. The FFT can be used to view the spectral content of a time domain measurement, Arta 1.2.