Good people;
I am using an older laptop running Ubuntu 12.10 to serve music via mpd
and alsa to a Schiit Bifrost DAC. I would like this to be "bit
perfect", ie, a 192kHz/24bit music file on the computer is passed
without alteration to the DAC for decoding.
Originally I had connected the pc and the DAC via USB. This almost
works the way I want it to, except a transition in rate doesn't quite
happen automatically - alsa sets a new bit rate but it's not correct.
Stopping and restarting the music always fixes the problem.
Today I acquired a used creative audigy 2 zs which apparently will
output up to 192kHz/24bit on its optical SPDIF out.
I installed it in my server and got music right away. However, I
think I am getting the music resampled somewhere along the way.
I believe this for two reasons.
First, I can use alsamixer to change the volume of the output, using
either the master or S/PDIF optical sliders, despite the following
configuration in /etc/mpd.conf
device "hw:2,0" # sometimes it's 2, depends on
load order at boot time
#format default is pass through
replay_gain_handler "none"
mixer_type "none"
auto_resample "no"
auto_channels "no"
auto_format "no"
buffer_time "1000000"
period_time "25000"
also interesting is that the slider called S/PDIF optical raw is
marked (off, off) (this is what I imagine I should be using to get
unprocessed bits flowing through
Second, the Schiit has a relay that apparently switches (clicking
audibly) when the bit rate changes (I am pretty sure I verified this
one day experimenting with another computer and an electrical S/PDIF
connection), but when I switch between songs with MPD I don't hear any
relay clicking.
There is a comment on
http://www.alsa-project.org/main/index.php/Matrix:Vendor-Creative_Labs
about this device, suggesting that digital PCM out works but that
maybe only 44.1 and 48 kHz rates are supported...
Anyway, I know this is an old unit, but does anyone have any ideas on
how to proceed? I'm willing to code...
--
Chris Hermansen · clhermansen at gmail dot com
C'est ma façon de parler.
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