A previous section explained that an IFIR filter is similar to a conventional FIR, but with the unit delay operator replaced by k -1 units of delay. k is referred to as the zero-packing factor. One way to realize this substitution is by the insertion of k -1 zeros between the coefficient values of a prototype filter. When specifying an IFIR architecture, the full set of prototype coefficients is supplied in the coefficient file, without the zeros implied by the zero-packing factor. The zero-packing factor is defined through the filter user interface. For example, consider the filter coefficient data in the .coe file shown in This Figure .
If a zero-packing factor of k =2 is specified, the equivalent filter impulse response is shown in This Figure .
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If the zero-packing factor is changed to k =3, the impulse response is as shown in This Figure .
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These examples use a symmetrical prototype impulse response; this is not a restriction of the filter core. The prototype filter coefficient set can be symmetrical, non-symmetrical, or negative-symmetric.