This work compared the performance of four similarity metrics for time domain pressure signals. The relative energy metric exhibits poor discrimination between signals and high sensitivity to random noise.The mean square error metricis also highly sensitive to random noise and phase error. The Weighted Structural Similarity Metric using a time frequency signal representation shows promise because it is resistant to contamination by random noise while still providing clear discrimination between time lags and frequency shifts, information pertinent to noise source model validation. Acknowledgments The authors thank the late Prof.John Fitzpatrick,who originated this project.D.B. also thanks Drs.Peter Jordan and André Cavalieri for their relevant discussions and help obtaining the experimental data. Science Foundation Ireland supported this work under contract 09/RFP/ENM2469.