The discrete wavelet packet transform iterates on both approximation and detail
coefficients at each level. In this transform, *A* denotes the
lowpass (approximation) filter followed by downsampling. *D*
denotes the highpass (detail) filter followed by downsampling. The figure represents
a wavelet packet transform in Paley ordering acting on a time series of length 8.
The transform has a depth of two.

Because of aliasing introduced by downsampling, the frequency content extracted by
the operator *AD* is higher than the frequency content extracted by
the *DD* operator. Therefore, the terminal nodes in frequency
(sequency) order are: *AA,DA,DD,AD*. The terminal nodes in Paley
order have the following indices: 3,4,5,6. The frequency order has the indices:
3,4,6,5.