Abstract: Apparatus and method for obtaining accurate sonic input data from a metallurgical furnace, for accomplishing accurate control of a lance injecting oxygen and/or other substances into the melt. A remotely located hydrophone is placed in sonic communication with a liquid circuit cooling the lance. Sound levels and frequencies are picked up through the liquid, and transmitted to a programmable logic controller which generates control signals operating the lance. An associated real time analyzer compares the sonic signature of the input data to predetermined sonic signature data retained in memory, and adjusts lance operation through the programmable logic controller accordingly in order to operate the furnace optimally. Sonic transmission is more accurate, and the hydrophone is more protected from the harsh furnace environment due to its remote location and employment of liquid sound transmission, when compared to other microphone arrangements.