5.2 - What is oversampling?
Description
This article is from the Audio Professional FAQ, by with numerous contributions by Gabe M. Wiener others.
5.2 - What is oversampling?
To take distortionless samples at 44.1kHz requires that the analogue
signal be bandlimited to 22.05kHz. Since the audio band is reckoned to
extend to 20kHz we require an analogue filter that cuts off very
sharply between 20kHz and 22kHz to accomplish this. This is expensive,
and suffers from all the ailments associated with analogue
electronics.
Oversampling is a technique whereby some of this filtering may be done
(relatively cheaply and easily) in the digital domain. By sampling at
a high rate (for example 4 times 44.1kHz, or 176.4kHz) the analogue
filter can have a much lower slope since its transition band is now
20kHz to 88kHz (ie half of 176kHz). The samples are then passed
through a digital filter with a sharp cutoff at 20kHz, after which
three of every four are discarded, resulting in the sample stream at
44.1kHz that we require. [Chris]
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