[Audio Empire]

On Sun, 28 Aug 2011 20:10:45 -0700, Robert Peirce wrote
(in article ):

I run Pure Music on my Mac. Presently, I use Airfoil to send the signal
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).

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 if
it can receive input from Pure Music or not. Does anybody know?

The way the Squeezebox works is that you pick a folder on your computer (Mac,
Windows or Linux) and designate it as your music folder in the Squeezebox
Touch music server software. Any supported format (and there are lots of them
but DSD files are NOT among them)) will then show up on the Squeezebox Touch
menu. So, if you pick whatever folder that Pure Music stores its music files
in as your designated Squeezebox server folder, and the files in it are WAVE,
FLAC, ALC, etc. and no more than 96KHz in sampling rate, it should work. What
I do is to use my iTunes folder as the Squeezebox Touch server folder, and I
put Apple Aliases of my "hi-rez" 24/96 files in the iTunes folder and those
files are then available right along with my iTunes catalog on my Squeezebox
Touch for playback. That way there is no need to actually move the files from
where they naturally reside or to duplicate them in order for the Squeezebox
Touch server software to find and use them.


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. It will also upsample 44.1/16 to 96/24. Or any
other standard sample rate and 16, 24 or 32 bit words.

Squeezebox server deals with files only. It does not interact with either the
iTunes application or any other program (including Pure Music). If Pure Music
allows you to make permanently altered copies of the files it manipulates or
up or down-samples to 96 KHz, then Squeezebox Touch will work with those
altered files. Be advised that the Logitech device only works with 96 KHz or
lower sample rates. What I do is use one of the digital outputs on the
Squeezebox Touch and feed that into a stand-alone up-sampling engine. Then I
feed the up-sampled 24/96 SPDIF signal to my outboard 24/192 DAC.

As far as I have been able to determine, the Squeezebox only passes
through what it receives, and that is great IF it can receive the output
from Pure Music. So, does anybody actually know if it can do that?

See above.

A related issue, but not critical, is that the software I am actually
running is Pure Vinyl. It is primarily designed for digitizing vinyl
recordings but it included Pure Music which I have grown to like a lot.
At present, I feed it directly from my pre-amp to the mic input on the
MAC, which works OK, but a two-way solution would be even better than
just using the player. Pure Vinyl can handle up to 384/32 if there is a
way to feed that to the Mac.

Tower Macs have have both an SPDIF input and output on them and should handle
384/32. However, be advised, that the only thing that such a high sampling
frequency buys you is huge digital files. Today's 32-bit is usually 24-bit
digital with an 8-bit floating-point mantissa. A 32 bit data stream records
65,000 times the dynamic range of a16 bit CD audio. This gives a dynamic
range that is so much higher than either the range of human perception or the
state-of-the-art noise floor in modern electronics that it's meaningless and
quite superfluous. It's like insisting that the film in your camera be able
to capture everything from the extreme infrared all the way out to X-Rays
when humans can only see red through violet light.

Also, while 32-bit may be enticing in the "more-has-got-to-be-better"
philosophy, most DACs can't handle true 32-bit and ignore the top 8-bits in a
32-bit floating point coding scheme. A rule of thumb that I have gleaned from
lots of experience and study is that 24-bit/48KHz quantization is
indistinguishable, audibly, from bit-depths higher than 24-bit or from
sampling rates higher than 48 KHz. Nobody's hearing is good enough to
distinguish any theoretical or practical advantage to frequency responses
that go much above 22KHz, or dynamic ranges that exceed 120 dB.

If 24-bit has any REAL WORLD advantage it is that it allows for lower peak
levels on recording which lessens the danger of over-modulation without the
resultant recording ending up down in the mud where distortion and
quantization noise increase as the signal toggles fewer and fewer bits.