## Hilbert Transform Relations

Closely related to the cepstrum are the so-called *Hilbert
transform relations* that relate the real and imaginary parts of the
spectra of causal signals. In particular, for minimum-phase spectra,
the cepstrum is causal, and this means that the log-magnitude and
phase form a Hilbert-transform pair. Methods for designing allpass
filters have been based on this relationship (see §B.2.2). For
more about cepstra and Hilbert transform relations, see
[60].

**Next Section:**

Pole-Zero Analysis Problems

**Previous Section:**

Conversion to Minimum Phase