Why do we use 44,1 kHz frequency on CDs while we’re only being able to hear up to 20 kHz?
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I can strongly recommend the following video from Monty Montgomery, on digital audio. At 23 minutes it brilliantly explains how it works, why it works, and how it’s made to work. He is succinct, clear and his demonstrations make it a 23 minute ELI5.
This is a textbook question of signal analysis!
Its the Nyquist frequency. In order to actually play at 20khz you need to sample it (record) at more than twice. So I guess technically 40.1khz would be ok, but I assume that 44khz is chosen for some error margin and likely historical compatibility with some other technology.
The reason is that if you a sine have a wave at 1hz and at 2hz then sampling at 2hz would give you exactly the same information for both waves. It gets even worse in that waves above 1hz will start looking like waves below 1hz. Its the kind of thing that’s really easy to see in a good diagram if you want further reading.
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