PhilNYC wrote:
Pat Farrell;131091 Wrote:
Nyquist showed that sampling at twice the bandwidth allows
reconstruction. That is why the RedBook spec uses 44.1 kHz.
For decades, the hfi world used a bandwidth of 20 hz to 20kHz
as the limits of human hearing. Sampling at 44.1kHz allows
a little over.
My understanding of the benefit of oversampling/upsampling is primarily
to get the digital artifacts resulting from imprecisions in the DAC
process to a higher frequency so that they can be more easily filtered
in a frequency range that won't impact the audible range.
I'm not an audio design engineer, so I could be wrong.
But I understand it exactly the opposite of this.
Digital processing has to have analog filters to cut out
unwanted signals and noise. If you use a 44.1kHz sample,
you need a radical filter to cut off signals about 20kHz.
The standard implementation uses 12dB/octave or even 18dB / octave
filters. These do evil things to phase.
So if you over/re/up-sample at 96kHz or 192kHz,
you can use digital filters (IIR, etc.) for the worst parts, and then
use gentle single order analog filters down in the 20-20kHz range.
One technical problem with the SACD spec was that it used noise shaping
to move the inevitable noise into relatively low frequencies (50kHz,
and up). which had potentential to have audible interactions.
Someone smarter than me can probably shed some light.
--
Pat
http://www.pfarrell.com/music/slimserver/slimsoftware.html
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