-Phase Filters
Under our definition, a zero-phase filter always has a real, even
impulse response [
], but not every real, even, impulse
response is a zero-phase filter. For example, if 
is zero
phase, then 
is not; however, we could call a
``-phase filter'' if we like (a zero-phase filter in series with
a sign inversion).
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Phase in the Stopband
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Implementation of Repeated Poles
