  We generalize quaternion and Clifford Fourier transforms to general two-sided
Clifford Fourier transforms (CFT), and study their properties (from linearity
to convolution). Two general \textit{multivector square roots} $\in \cl{p,q}$
\textit{of} -1 are used to split multivector signals, and to construct the left
and right CFT kernel factors.
  Keywords: Clifford Fourier transform, Clifford algebra, signal processing,
square roots of -1 .
