[Mp4-tech][audio] High sampling rates in AAC - why?

[Magnus Hoem]

Hi!
I think you have confused two different values. It is true that humans  
can't hear much above 20 kHz, but that is not directly related to  
sampling frequency. The sampling frequency really just states how many  
times per second you sample the analog soundwave. This means that for  
96 kHz sampling frequency you sample 96000 times a second and you can  
code audio with frequencies up to half of that (Nyqvist frequency or  
whatever it is called) without distortion. However audio at more  
"normal" frequencies can also be represented, and this with better  
quality since it is closer to the original soundwave.
Best regards,
Magnus
On Oct 26, 2004, at 12:11, D.Domazet wrote:
> Hi all,
> As we know, AAC supports high sampling rates, for example 88.2kHz and  
> 96kHz.
> What is the purpose of this? If I was to test the encoder for quality  
> at
> this sampling rates, how would I do that? Is down-sampling a must since
> humans can't hear this high freqs? Or AAC is used by bats and whales...
>
> Daniel
>
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