About wavelet transformation
A wavelet transform (WT) of an AE signal provides information which wave modes carry significant energy and where in a mode the energy as a function of frequency and time is to be found.
About Choi-Williams transformation
The time-frequency transformation called Choi-Williams transform as proposed by Hyung-Ill Choi and William J. Williams and first published in IEEE Transactions on Acoustic Speech and Signal Processing Vol. 37, No. 6, June 1989. The advantage of the Choi-Williams transformation is the improved resolution of frequency vs. time. A minor drawback is the less sensitive energy resolution.