A method and apparatus for processing acoustic data recorded by a subterranean receiver array. The method includes emitting an acoustic signal into a formation, receiving the signal after it passes through the array, and processing the data with semblance and phase velocity processing. Semblance and phase velocity plots are generated and combined into a single plot. The phase velocity processing creates phase separation lines, the phase separation line that crosses the closest contour of the semblance plot is identified. The point where the intersecting phase separation line crosses an associated tool line marks the slowness and travel time that provides maximum coherence.