[opus] High Sampling Rates

Monty Montgomery monty at xiph.org
Mon Jun 9 02:12:57 PDT 2014

> With higher sampling rates, it gives us flexibility to design this filter such that the stopband attenuation is large enough (although not –infinite dB) and the noise is filtered to inaudible levels.

This is an argument for higher sampling rates in conversion, as an
implementation detail, not the data stream.  The sampling and
reconstruction rates are asynchronous with the actual PCM data rate;
modern DACs run at several MHz even when the input data is 44.1kHz
redbook.  ADCs likewise.

In software, filters that roll off 100dB between 20kHz and 20.5kHz are
trivial. Yes, perfect filters aren't realizable, but there's not much
point in quibbling beyond 140 of broadband SNR.  1kohm resistors
inject more noise.


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