GUIDE: Mathematics of the Discrete Fourier Transform (DFT) - Julius O. Smith III. Zero Padding

It appears that you are using AdBlocking software. The cost of running this website is covered by advertisements. If you like it please feel free to a small amount of money to secure the future of this website.

NOTE: THIS DOCUMENT IS OBSOLETE, PLEASE CHECK THE NEW VERSION: "Mathematics of the Discrete Fourier Transform (DFT), with Audio Applications --- Second Edition", by Julius O. Smith III, W3K Publishing, 2007, ISBN 978-0-9745607-4-8. - Copyright © 2017-09-28 by Julius O. Smith III - Center for Computer Research in Music and Acoustics (CCRMA), Stanford University

<< Previous page  TOC  INDEX  Next page >>

Definition: Zero padding consists of appending zeros to a signal. It maps a length signal to a length signal, but need not be an integer multiple of :

For example,

The above definition is natural when represents a signal starting at time and extending for samples. If, on the other hand, we are zero-padding a spectrum, or we have a time-domain signal which has nonzero samples for negative time indices, then the zero padding is normally inserted between samples and for odd (note that ), and similarly for even . I.e., for spectra, zero padding is inserted at the point ( ). Figure 8.5 illustrates this second form of zero padding. It is also used in conjunction with zero-phase FFT windows(discussed a bit further below).

Using Fourier theorems, we will be able to show that zero padding in the time domain gives bandlimited interpolation in the frequency domain. Similarly, zero padding in the frequency domain gives bandlimited interpolation in the time domain. This is how ideal sampling rate conversion is accomplished.

It is important to note that bandlimited interpolation is idealinterpolation in digital signal processing.

<< Previous page  TOC  INDEX  Next page >>