General Causal FIR Filters

The most general case--a TDL having a tap after *every* delay
element--is the general causal *Finite Impulse Response (FIR)*
filter, shown in Fig.2.22. It is restricted to be *causal*
because the output
may not depend on *``future''* inputs
,
, etc. The FIR filter is also called a
*transversal filter*. FIR filters are described in greater
detail in [452].

The *difference equation* for the
th-order FIR filter in Fig.2.22
is, by inspection,

and the

The STK class for implementing arbitrary direct-form FIR filters is
called Fir. (There is also a class for IIR filters named Iir.)
In Matlab and Octave, the built-in function `filter` is
normally used.

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