Okay, I decide that I want to build myself a new MP3 jukebox thing
for my livingroom. I start with one of those spiffy Via mini-ITX
boards, it's only 170mm x 170mm and can run with no fan if you
use the version with the 533MHz Eden processor. I'm running it diskless
and booting linux off the PXE ROM in the BIOS, it's great, small,
dead quiet, commodity, a real jukebox possibility.
I'm running alsa-0.90rc3 audio drivers on a 2.4.19 kernel, works
great. The mini-ITX board has spdif output (if you move a jumper).
My plan is to use svideo and sdpif outputs and send them to an
a/v receiver.
The alsa stuff works great on the VT8231 south-bridge and VT1612A
AC-97 codec (via686 driver). The problem starts when I enable the
spdif output on the board. The spdif output works, and at first
blush the sound is reasonable, but after listening for awhile, there
are quite a few sound artifacts on the spdif output not present on the
analog line output.
To my ear it sounds like crappy sample rate conversion, little extra
harmonic sounds that go along with the music. I don't think I'm
being super picky, I think anyone could hear if they listen closely
for a minute. There are no pops or clicks, just the extra digital harmony
along with the music. The analog line output sounds fine.
So, I notice that the spdif output from the board is at 48kHz, but
mpg123 (or madplay) is decoding a file at 44100. On the motherboard
there is a 24.576MHz crystal next to the codec (48kHz x 512). I'm a
little knew to this stuff and I'm starting to own up to the inevitable,
but I've got a couple questions for others that have been down this
path:
a) Is it really true that a typical Via VT8231/VT1612A
implementation can only do 48kHz spdif output?
b) Where is the crappy sample rate conversion being done? Is
the codec trying to do this and doing it poorly?
c) Why does the analog line output sound so good and the spdif
sound so much worse? I would think that both the DAC and the
spdif output would use the same 48kHz clock and sample rate
conversion hardware?
d) Is there a datasheet on the VT1612A? I can't seem to find one
anywhere? The ac97-codec.c source code has a small note
saying that a VIA1612A is an ICE1232 with spdif.
e) Is there a high-quality software sample rate convertor I might
use with alsa for doing 44.1k -> 48k and making an MP3 jukebox?
f) What is the simplest path to getting an alsa-compatible spdif
output that can really do 32kHz, 44.1kHz, and 48kHz properly? The
mini-itx motherboard does have a pci slot, but I had hoped to
not use it.
There, I've rattled on too long, PC audio really annoys me now and then.
jeff
-------------------------------------------------------
This sf.net email is sponsored by:ThinkGeek
Welcome to geek heaven.
http://thinkgeek.com/sf
_______________________________________________
Alsa-user mailing list
[EMAIL PROTECTED]
https://lists.sourceforge.net/lists/listinfo/alsa-user
