Causal FIR Filters

From Eq.$ \,$(5.6), we see also that the impulse response $ h(n)$ is always zero for $ n < 0$. Recall from §5.3 that any LTI filter having a zero impulse response prior to time 0 is said to be causal. Thus, a tapped delay line such as that depicted in Fig.5.5 can only implement causal FIR filters. In software, on the other hand, we may easily implement non-causal FIR filters as well, based simply on the definition of convolution.

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The ``Finite'' in FIR