Have a look at http://en.wikipedia.org/wiki/Whittaker%E2%80%93Shannon_inter... .

"The Whittaker–Shannon interpolation formula or sinc interpolation is a method to construct a continuous-time bandlimited function from a sequence of real numbers."

http://en.wikipedia.org/wiki/Reconstruction_filter has a less mathematical explanation, but, as Monty mentions in the video, be wary of the sentence "in practice, the output of a DAC is more typically a zero-order hold series of stairsteps". This really only applies to some (mostly low-end) DACs. There are many DACs that will use anti-aliasing / interpolation and probably many other methods to recreate the signal.

Thanks, exactly what I was searching for. Quoting from "Reconstruction filter" page:

  Practical filters have non-flat frequency or phase
  response in the pass band and incomplete suppression
  of the signal elsewhere. The ideal sinc waveform [..]
  would require infinite delay.

So it's all good in theory, and it depends in practice. Any idea what is the highest frequency "recomended" in a typical audio that will not cause trouble for consumer grade DACs?

That is, if I'm mastering, say, for 44.1kHz, what is the recomended antialiasing filter?