NOTE: THIS DOCUMENT IS OBSOLETE, PLEASE CHECK THE NEW VERSION: "Mathematics of the Discrete Fourier Transform (DFT), with Audio Applications --- Second Edition", by Julius O. Smith III, W3K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
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Stretch OperatorUnlike all previous operators, the operator maps a length signal to a length signal, where and are integers. We use '''' instead of '''' as the time index to underscore this fact.
Definition: A stretch by factor is defined by
Thus, to stretch a signal by the factor , insert zeros between each pair of samples. An example of a stretch by factor three is shown in Fig. 8.4. The example is
The stretch operator is used to describe and analyze upsampling, i.e., increasing the sampling rate by an integer factor.