Note that only the spectral *magnitude* is used to find
in
the parabolic interpolation scheme of the previous section. In some
applications, a *phase* interpolation is also desired.

In principle, phase interpolation is *independent* of magnitude
interpolation, and any interpolation method can be used. There is
usually no reason to expect a ``phase peak'' at a magnitude peak, so
simple linear interpolation may be used to interpolate the
*unwrapped* phase samples (given a sufficiently large
zero-padding factor). Matlab has an `unwrap` function for
unwrapping phase, and §F.4 provides an Octave-compatible
version.

If we do expect a phase peak (such as when identifying *chirps*,
as discussed in §10.6), then we
may use quadratic interpolation separately on the (unwrapped) phase.

Alternatively, the real and imaginary parts can be interpolated separately to yield a complex peak value estimate.

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