Impulse Response Example
An example impulse response for the first-order recursive filter
is shown in Fig.5.2b. The impulse response is a sampled exponential decay,

![$\displaystyle h(n) = \left\{\begin{array}{ll}
(0.9)^n, & n\geq 0 \\ [5pt]
0, & n<0. \\
\end{array}\right.
$](http://www.dsprelated.com/josimages_new/filters/img550.png)
![$\displaystyle u(n) \isdef \left\{\begin{array}{ll}
1, & n\geq 0 \\ [5pt]
0, & n<0 \\
\end{array}\right.,
$](http://www.dsprelated.com/josimages_new/filters/img551.png)



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