if *h*(*n*) is real, as in most speech processing, is
symmetric. Most useful.

Similarly, if *h*(*n*) is even, i.e. *h*(*n*) = *h*(-*n*) then
is real.

Fourier transforms of real valued data can be done roughly twice as fast (only half the complex numbers are present) - look for realft in Numerical recipes.

Speech Vision Robotics group/Tony Robinson