Windowing_FFTs - Windowing with FFTs Author: John M....

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Windowing with FFTs Author: John M. Cimbala, Penn State University Latest revision: 28 February 2007 Introduction When performing FFTs, the sampled time signal does not always start and end at exactly the same phase of the signal. This leads to an error in the frequency spectrum called leakage , in which peaks in the spectrum are spread out, and are therefore not as sharply defined as they should be. The goal of windowing is to reduce the effect of leakage ; we discuss windowing in this learning module. Windowing for signals with no DC offset Can leakage be reduced without increasing the number of sampled data points N or the sampling time T ? The answer is yes , through a process called windowing . As mentioned previously, the cause of leakage is that the signal starts and ends at different phases in the cycle. In most experiments, the sampling rate and number of data points is such that this cannot be avoided. However, if the amplitude of the signal at both ends (near t = 0 and near t = T ) is reduced to zero in a smooth fashion, the end effects will not be as serious. This is the fundamental concept of windowing. In practice, the signal is multiplied by a windowing function , which starts at zero at t = 0, increases smoothly to 1 at t = T /2, and then decreases smoothly again to zero at t = T .
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 07/23/2008 for the course ME 345 taught by Professor Staff during the Spring '08 term at Pennsylvania State University, University Park.

Page1 / 2

Windowing_FFTs - Windowing with FFTs Author: John M....

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online