The electromagnetic acoustic resonance (EMAR) method using an electromagnetic acoustic transducer (EMAT) has been proposed to perform pipe wall thickness measurements. However, in some parts of pipes, identification of the resonance frequency can be a difficult task. In this paper, a new data processing method called multiplication of n^th compression (MNC) is proposed to determine the resonance frequency. The performance of the MNC method is compared with that of the previously used autocorrelation function (ACF) and superposition of n^th compression (SNC) methods in two experiments. Finally, a two-step data processing procedure for use in pipe wall thickness measurements is proposed. This procedure can improve the data processing accuracy.