Introduction - If you have any usage issues, please Google them yourself
Design a two-channel QMF filter bank
The four filters in the filter bank are based on a lowpass prototype H(z)
which is designed by this procedure. The analysis filters are HL(z) and
HH(z) and the synthesis filters are GL(z) and GH(z),
HL(z) = H(z) HH(z) = H(-z)
GL(z) = 2 H(z) GH(z) =-2 H(-z