> George Brock-Nannestad
> It has to reduce signal components at 22.05 kHz to
> below LSB. This filter smears any high frequency
> energy, such as that in a click, over a wide frequency
> band below 20 kHz. The higher sampling rates can and do
> use much less steep filters.
This is a myth.
A brickwall 20 kHz antialias filter will only ring at 20 kHz.
There is no smearing lower down.
It is very easy to prove this by looking at the pre and post ringing of
such a filter and calculate the frequency of the ringing.
It will be found that this ringing is sitting at the filter cutoff
frequency and nowhere else.
BTW, good 20 kHz antialias filters can easily be made inaudible. One do
this by not allowing ripple in the transfer function.
Ripple is far more audible giving rise to pre and post echoes that are
much greater in magnitude than the very slight ringing from the cutoff
of the filter alone.
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