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Anyone here who has not already seen Xiph's Digital Show and Tell ( http://xiph.org/video/vid2.shtml ) should do themselves a favor and sit down for a watch. It makes sense of a lot of mysteries and misconceptions around digital audio.


Starting with the first video of the series is probably a good idea, it's aptly named "a digital media primer for geeks"

http://xiph.org/video/ for the series.


Though vid2 was specifically made to address misunderstandings from this article.


So I watched, and I'm confused. How exactly does DAC recreate a band limited signal without having an infinite lookahead? Honest question. Any pointers?


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?


Cool video, ta.




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