# Translations:Sampling geophysical data/3/en

Next, we look at the process of reconstructing a continuous signal from sampled data. An antialias filter is applied *before* the sampling process — it should remove the high-frequency components that the sampling process otherwise would alias. That is, an antialias filter effectively should remove all frequencies above the Nyquist frequency. As an example, let us suppose that the sampling interval is 0.004 s. The Nyquist frequency is 125 Hz for this time interval. The original continuous signal must be low-pass-filtered by an antialias filter that effectively destroys all harmonic components above 125 Hz. In this way, these high frequencies will not appear as aliases in the Nyquist range. The basic theorem on sampling theory then states that the original filtered signal can be reconstructed from the sampled data.