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In the previous section we superposed uniformly spaced frequencies.
Now we will **superpose** delayed impulses.
The frequency function of a delayed impulse at time delay *t*_{0}
is .Adding some pulses yields the ``**Fourier sum**'':
| |
(19) |

The Fourier sum transforms the signal *b*_{t}
to the frequency function .Time will often be denoted by *t*, even though
its units are sample units instead of physical units.
Thus we often see *b*_{t} in equations like (19) instead of *b*_{n},
resulting in an implied .

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Stanford Exploration Project

10/21/1998