[Audio Empire]

On Mon, 29 Aug 2011 04:56:46 -0700, Edmund wrote
(in article ):

On Mon, 29 Aug 2011 03:10:45 +0000, Robert Peirce wrote:

I run Pure Music on my Mac. Presently, I use Airfoil to send the signa=
l
over ethernet to my AppleTV. The AppleTV has an optical output to my
DAC. Pure Music and my DAC both support 96/24, but the Apple TV only
does 44.1/16 (or, maybe, 48/16 - hard to find specs).
=20
I have been trying to find a substitute for the AppleTV, but so far all
I have got is the Squeezebox Touch. I say "but" because it has its own
software that resides on the Mac and I have not been able to find out i=
f
it can receive input from Pure Music or not. Does anybody know?
=20
The web site suggests the Squeezebox can read any file on the computer,
which is great, except Pure Music already does that and allows many
useful manipulations. For example, it will accept up to 384/32 and
downsample it to 96/24.

I wonder what happens to the anti alias filter in that case.

Edmund


You would certainly have to move the filter up in frequency in order to use
that extra bandwidth, otherwise the filter would simply treat the signal like
any other digital audio stream and start to roll-off the frequency response
above 22 KHz. What the use of high sampling rates does is to move any
quantization noise further out of the passband as the sampling rate
increases. Whether this is of any practical consideration is debatable.
Double-blind tests seem to show that this is no real consequence, but some
will hotly debate the point.

Seems to me that I read somewhere that modern 24/192 DAC chips move the
antialiasing frequency as the sample rate increases. If it didn't do that and
left the antialiasing filter "cutoff" at 22.05 KHz (which is normal for
16-bit/44.1 KHz CD) then any advantage (real or imagined) to higher bit-rate
audio would be wasted as everything would be severely rolled off above 22.05
KHz regardless of bit rate. .