Multiple choice

Consider a four-point moving average filter defined by the following equation:

$y[n] = \sum_{i = 0}^3 a_ix[n - i]$

The condition on the filter coefficients that results in a null at zero frequency is

  1. $a_1$ = $a_2$ = 0; $a_0$ = – $a_3$
  2. $a_1$= $a_2$ = 1; $a_0$ = – $a_3$
  3. $a_0$ = $a_3$ = 0; $a_1$ = $a_2$
  4. $a_1$ = $a_2$ = 0; $a_0$ = $a_3$
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