A system for active noise blocking of top drive acoustical waves includes a first accelerometer for detecting a first acoustical wave generated by the top drive of a drilling rig. A second accelerometer detects a second acoustical wave after the first acoustical wave has interacted with an anti-wave. An active noise blocking generator generates the anti-wave responsive to the detected first acoustical wave and the detected second acoustical wave and applies the anti-wave to the first acoustical wave. The anti-wave is generated to drive the second acoustical wave to zero responsive to application of the anti-wave to the first acoustical wave.