### Ideal Spectral Interpolation

Ideally, the spectrum of any signal at any frequency is obtained by projecting the signal onto the zero-phase, unit-amplitude, complex sinusoid at frequency [264]:

 (3.43)

where

Thus, for signals in the DTFT domain which are time limited to , we obtain

 (3.44)

This can be thought of as a zero-centered DFT evaluated at instead of for some . It arises naturally from taking the DTFT of a finite-length signal. Such time-limited signals may be said to have finite support'' [175].

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