Structure-borne sound is sound spreading within a solid body. Structure-borne sound may be detected by humans as a vibration (by touching the object) up to a certain frequency. Structure-borne sound is created by machining processes such as milling, drilling, grinding, etc. Monitoring of structure-borne sound is a reliable diagnostic tool for process analysis. It provides information about a tool condition, registers the contact between the tool and the work piece, and it detects machine errors in geometry and defective bearin