About Windowing in Fast Fourier Transforms

Figure 1: Windowing a waveform that's not periodic within
the acquisition window reduces spectral leakage

The second artifact in FFT calculations is more serious and is also the source of some confusion. A good source for information on this topic of windowing is an application note published by National Instruments.

About Data Truncation in Fast Fourier Transforms

Figure 1: The first precondition of using the Fourier transform
is a repetitive signal

Our last post discussed how time-domain signals acquired by an oscilloscope might be translated into the frequency domain using the discrete Fourier transform. We noted that using the Fourier transform only works if our signal is repetitive (Figure 1), and that it allows us to identify only harmonics of the first harmonic frequency, which is 1/acquisition window. Moreover, the discrete Fourier transform, if used on a large number of data points, is relatively slow to calculate.