A device-implemented method for monitoring the cutting condition of a machine tool during machining of a workpiece senses acoustic emissions resulting from the machining of the workpiece, produces an electrical signals which varies in accordance with changes in the sensed acoustic emissions, and variably amplifies the signal by a gain level selected by a set of digital data stored in the memory (12) of a computer (15). The signal is amplified by an amplifier (32) having a variable gain input (34) controlled by the computer (15). The signal is processed by two circuits (36, 40, 56 and 36, 42, 50) which respectively generate two separate sets of digital data representing the cutting condition of the tool. The computer (15) compares the data with memory-stored information to determine whether an alarm signal should be generated. A circuit (75) is provided for generating a control signal indicating that cutting of the workpiece has commenced.