Quality control remains a topic of concern in additive manufacturing, particularly for emerging additive methods and materials that require process validation and final part quality verification. Monitoring acoustic signatures during a manufacturing process has been successfully applied in a number of processes including cutting, milling, laser processing, and to a lesser extent, additive manufacturing. Results from a proof-of-concept study for on-line real-time of acoustic monitoring of a directed energy deposition will be reported which demonstrates that acoustic signatures contain information on the machine, process, and fabricated material state. Signal processing of acoustic signatures taken during deposition in a DED process are also shown to correlate well with discrete defects associated with crack initiation during deposition of dissimilar materials. The experimental results for process state determination and acoustic signature correlation with defects for a DED additive manufacturing process were obtained using commercially available acoustic emissions sensors and a passive monitoring technique.