New beam shaping technologies enable the adjustment of the laser intensity distribution in laser beam welding processes to optimize the shape of the keyhole and, thus the melt pool shape and melt flow. Dynamic beam shaping by coherent beam combining allows for almost limitless freedom in adjusting the intensity distribution on the workpiece surface in space and time. To achieve high quality welds, without spatters, cracks and undercuts, it is crucial to understand the keyhole and melt flow dependence on the frequency of the applied beam shape changes. E.g. at some hundred Hz frequency the keyhole shape follows beam shape changes, whereas frequencies of above 10 kHz result in the creation of quasi-static beam shapes, which are not connected with correspondingly frequent changes of the keyhole shape. The impact of rapid beam shape modulation in previously inaccessible frequency ranges has not yet been thoroughly investigated. This study examined the frequency dependent response of the melt pool geometry to periodic changes of the beam shape by means of high-speed imaging. The findings outline the frequency-dependent process regimes for dynamic beam shaping in laser welding of steel and aluminum. The gained knowledge of process response in the different regimes is crucial to enable optimization of dynamic laser welding processes.