I'm not an expert, but I think there are two parts to this. First, "oversampling", meaning that in the digital domain one calculates extra samples in between th

I'm not an expert, but I think there are two parts to this. First, "oversampling", meaning that in the digital domain one calculates extra samples in between the given ones to make the "staircase" distortions smaller (see https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/iandm/pdf/chapter11.pdf https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/iandm/pdf/c...). Second, in the analog domain one applies a low-pass "reconstruction filter", similar to the ones used before sampling. The idea is that the noise added by the staircase effect will be high-frequency, and can be filtered out by removing frequencies above the nyquist rate.