An [[acoustic]] log. A well-logging record of the [[travel time]] ([[interval transit time]]) of the [[compression wave]] over a unit distance: and hence, a record of the reciprocal of the compressional wave velocity. The time for acoustic energy to travel a distance through the [[formation]] equal to the distance spanned by two [[receiver|receivers]] is the desired measurement. The units of such measurement are usually expressed in microseconds per foot. The interval transit time can be [[integrate|integrated]] to give the total travel time over the logged interval. For the [[borehole compensated sonic log]], two [[transmitter|transmitters]] (one above the receivers and one below) are pulsed alternately to produce an improved log; averaging the measurements tends to cancel errors due to [[sonde]] tilt or changes in hole size.

The sonic log is used in combination with other logs (e.g., density and neutron) for [[porosity]], shaliness, and [[lithology]] interpretation. [[interval transit time|Integrated transit time]] is helpful in interpreting seismic records. See [[acoustic log]].

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