An improved non-destructive sonic testing apparatus is disclosed which is specially adapted for use in assessing the integrity of wooden utility poles. In one embodiment, the sonic testing apparatus of the present invention operates to perform a Fourier analysis on a signal which has been transmitted through a pole to be tested. Two or more criteria selected from the group of mode, mean, median and range are then determined for the resulting waveform and compared in order to provide a visual display representative of the condition of the pole being tested. In another embodiment of the present invention a software peak seeking algorithm is utilized to provide an envelope waveform from which successive half lives are determined. The relative time duration for successive half lives are compared to provide an indication of the amount of decay.