1. A method of determining properties of rock in a formation in real-time during drilling, the method comprising the steps of: receiving raw acoustic sensor data from one or more acoustic sensors by a downhole processor assembly, the one or more acoustic sensors carried by a downhole sensor subassembly positioned adjacent a drill bit and between a drill string and the drill bit, the downhole processor assembly positioned in close proximity to the one or more acoustic sensors and operably coupled thereto, the raw acoustic sensor data representing an acoustic signal generated real-time as a result of rotational contact of a drill bit with rock during drilling; and processing the raw acoustic sensor data by the downhole processor assembly, the processing including deriving a plurality of acoustic characteristics associated with the rock from the raw acoustic sensor data, the plurality of acoustics characteristics including mean frequency and normalized deviation of frequency; transmitting the plurality of acoustic characteristics to a surface computer over a borehole telemetry system, wherein the surface computer is configured to output a plot of at least one of the plurality of acoustic characteristics versus depth; performing one or more of the following processing steps at the surface computer; identifying lithology type of rock being encountered by the drill bit utilizing one or more of the following sets of acoustic characteristics of the plurality of acoustic characteristics: the mean frequency and the normalized deviation of frequency, the mean frequency and mean amplitude, the mean frequency, the mean amplitude, the normalized deviation of frequency, normalized deviation of amplitude, and apparent power, and deriving petrophysical properties of rock being encountered by the drill bit utilizing a petrophysical properties evaluation algorithm employable to evaluate one or more petrophysical properties of rock undergoing drilling utilizing one or more of the plurality of acoustic characteristics.