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Comment by ta2112 | Hacker News Reader

> that’s why CD music had a sample rate of 22000 Hz. Modern sound cards however tend to use sampling rates twice as high - 44100 Hz or 48000 Hz or even 96000 Hz.

Not exactly the point of the article, but this is all sort of wrong. CDs use a sample rate of 44.1 kHz per channel, not 22 kHz. I'd hazard this cuts down on rounding errors from having only one sample per 22kHz range. DAT used 48 kHz I believe to align evenly with film's 24 frames per second. 96 kHz is commonly used for audio today, and the additional accuracy is useful when editing samples without producing dithering artifacts within human hearing range.

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CDs use 44.1kHz because your sample rate needs to be double the highest frequency you want to encode to avoid aliasing artifacts: https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampli...

20kHz is the top of the human hearing range, and picking something a little bit higher than 40kHz gives you room to smoothly roll off frequencies above the audible range without needing an extremely steep filter that would create a large phase shift.

In practice, artifacts become common past something like 16 kHz. I'm not sure how much of this is math and how much is that almost all speakers are made very cheaply.

You do in fact need an extremely steep filter. 44.1kHz is a little over an octave above 20k, and for adequate filtering and reconstruction you need 96dB of roll-off at at 16-bits and 144dB at 24-bits.

It's practically impossible to design an artefact-free filter with a roll-off as steep as that. Every single person who says that 44.1k is enough "because Nyquist" has failed to understand this.

You can trade off delay against various artefacts, including passband ripple, non-linear phase smearing, and others. But the shorter the delay, the less true it is that you get out exactly what you put in.

44.1 was selected because it was a viable rate for recording on both PAL and NTSC video recorders gently modified to capture digital audio on tapes that were sent out to the mastering plants. There is nothing otherwise special about it.

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