Left: comparison of observed GOLF solar velocities (black) and synthetic velocities extracted from 3D simulationsof the granulation (red). The acoustics modes have been filtered out using a low-pass filter of 1620 μHz passband and a WGN has been added to both series. Right: associated averaged periodograms computed with L = 26 time series of 2 days duration. The grey PSD shows the averaged periodogram resulting from the unfiltered GOLF observations, where we can see the acoustics modes velocity signatures around 2000− 6000 μHz. The dotted line indicates the frequency regime where the high-frequency noise has been artificially added to both time series. The dashed line indicates the frequency limit (ν = 56 μHz) where the PSD is no longer dominated by the granulation noise.