A
zero-phase signal is thus a
linear-phase signal for which the
phase-slope

is zero. As mentioned above (in
§
7.4.3), it would be more precise to say ``0-or-

-phase
signal'' instead of ``zero-phase signal''. Another better term is
``zero-centered signal'', since every real (even)
spectrum corresponds
to an even (real) signal. Of course, a zero-centered symmetric signal
is simply an
even signal, by definition. Thus, a ``zero-phase
signal'' is more precisely termed an ``even signal''.

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