1. In a system for acoustic logging of an earth formation comprising a transmitter creating acoustic energy and a plurality of receivers recording time domain representations of the acoustic energy as it traverses the earth formation, a method of signal processing to determine acoustic velocity as a function of frequency comprising: converting the time domain representations of the acoustic energy into frequency domain representations; creating a correlation matrix from amplitudes within the frequency domain representations at corresponding frequencies; finding an orthogonal basis of the correlation matrix comprising a plurality of component functions; removing at least one component function to create a subspace; and multiplying a test vector and the subspace, the test vector based on an estimated acoustic velocity of the earth formation, to determine whether the estimated acoustic velocity substantially matches the actual earth formation acoustic velocity.