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What is the meaning of a pole?
We will see that the location of poles
determines whether filters are stable
(have finite output) or unstable
(have unbounded output).
Considering both positive and negative values of ,we find that
stability is associated with .The pole happens to be real,
but we will soon see that poles
are complex more often than not.
In the case of complex poles, the condition of stability
is that they all should satisfy |*Z*_{p}|>1.
In the complex *Z*-plane,
this means that all the poles should be outside a circle of unit radius,
the so-called **unit circle**.

** Next:** The mapping between Z
** Up:** INSTABILITY
** Previous:** Inverse filters
Stanford Exploration Project

10/21/1998