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Anti-aliasing filter 抗混疊濾波器

The low-pass filter in front of an analogue-to-digital converter, removing everything above half the sample rate before sampling can fold it down into the audible band as a frequency that was never present. Aliasing is unrecoverable once it has happened, which is why the filter is in hardware and ahead of the converter. A steep filter close to the band edge is difficult to build cleanly, which is the real engineering argument for higher sample rates: they let the filter be gentle and start well above hearing.

中文

置於類比數位轉換器之前的低通濾波器，在取樣之前濾除高於取樣率一半的所有成分，以免這些成分 被折返到可聽頻段，成為原本並不存在的頻率。混疊一旦發生便無法還原，因此這個濾波器必須是硬 體、且位於轉換器之前。緊貼頻帶邊緣的陡峭濾波器難以做得乾淨，這正是提高取樣率的真正工程理 由：可讓濾波器和緩，並自遠高於聽覺上限之處開始作用。

Regional usage

Easy to get wrong

Sources

• AES standards for audio engineering — Audio Engineering Society primary