When metal cutting is performed, the machining processes introduce productivity degrading vibration. By applying an active control scheme, theses vibrations can be reduced significantly with the result of improved surface finish of the work piece and increased tool life. Due to the large difference of boundary conditions during the machining process, a controller fast enough to follow these changes is needed, for example from no cutting to cutting - the actual engagement of the cutting process. If the controller does not success to follow fast enough, the tool tip might break, as is the case without any active damping. Different approaches based on feedback control are investigated; all implemented using an active boring bar. The first approach is based on a digital adaptive feedback controller; the feedback filtered-X LMS algorithm. The two other controllers are analog; one is a lead controller and the other is lead-lag controller, both with gain and phase orthogonally adjustable. This paper focuses on robustness, stability and convergence of the digital and the analog feedback controllers. The analysis is based on open loop frequency response function estimates during different operating conditions.