1. An apparatus for identifying rock properties in real-time during drilling, the apparatus comprising: a downhole sensor subassembly connected between a drill bit and a drill string; one or more acoustic sensors carried by the downhole sensor subassembly and operably coupled to a downhole data interface; a downhole processor assembly operably coupled to the one or more acoustic sensors and operably coupled to a downhole data transmitting interface, the downhole processor assembly adapted to perform the following operations: receiving digitized raw acoustic sensor data from the one or more acoustic sensors, the raw acoustic sensor data representing an acoustic signal generated real-time as a result of rotational contact of the drill bit with rock during drilling, and processing the raw acoustic sensor data, the operation of processing including deriving a plurality of acoustic characteristics from the processed raw acoustic sensor data, the plurality of acoustic characteristics including mean frequency and normalized deviation of frequency; and a surface computer operably coupled to the downhole data transmitting interface through a surface data transmitting interface and a communication medium extending therebetween, the computer configured to perform the following operations: receiving acoustic characteristics data from the downhole processor assembly, performing one or more of the following processing operations at the surface computer: identifying lithology type of rock being encountered by the drill bit utilizing the mean frequency and the normalized deviation of frequency, and deriving petrophysical properties of rock being encountered by the drill bit from the acoustic characteristics data utilizing a petrophysical properties evaluation algorithm employable to predict one or more petrophysical properties of rock undergoing drilling utilizing one or more of the plurality of acoustic characteristics.