response. The length-11 impulse response is shown in fig. 12.

operations "multiply-and-accumulate", often called MAC. In order to run an

N-th order FIR filter we need to have, at any instant, the current input sample

together with the sequence of the N preceding samples. These N samples con-

stitute the memory of the filter. In practical implementations, it is customary

to allocate the memory in contiguous cells of the data memory or, in any case,

in locations that can be easily accessed sequentially. At every sampling instant,

the state must be updated in such a way that x(k) becomes x(k - 1), and this

seems to imply a shift of N data words in the filter memory. Indeed, instead of

moving data, it is convenient to move the indexes that access the data. Consider

the scheme depicted in fig. 13, which represents the realization of an FIR filter

of order 3.