[mythtv-users] Cheap & simple solution for Optical SPDIF output

[Willy Boyd]

I'm posting this for the sake of anyone that might search for this
sort of thing, as this was one of those few things I couldn't find an
answer online and just kind of stumbled on it.

First, some background.  In my backend I have an SB Live! 5.1 card,
which can do coax digital sound output, but for my receiver I needed
an optical connection.  This presented a couple of options.  First, I
came across a cheap coax-to-optical converter:

http://www.monoprice.com/products/product.asp?c_id=104&cp_id=10423&cs_id=1042302&p_id=2947&seq=1&format=2&style=

But that requires it's own power (as far as I can tell), a coax cable
and probably an adapter to get the small spdif on my SB to a normal
RCA-type jack... and takes time to ship.  The impulsive part of me
just wanted to hit a store and grab something.  So, the next option
was the Turtle Beach Riviera, which has a full optical jack on the
card, and runs about $30 in stores.  But of course every place I went
to just didn't have one.  Then I found myself in CompUSA... they
didn't have the card either, but did have this little gizmo:

http://www.turtlebeach.com/site/products/audioadv/micro/
$29.99 when I got it at CompUSA.

A USB soundcard, with full optical toslink jack (with included
adapter).  Now the problem was, no where could I find a conclusive yes
or no whether the optical worked in linux.  I even saw some reports
that it didn't, but those were dated, and saw a mention of a patch to
ALSA where someone got it working on a similar Turtle Beach device (I
forget the model name), so I figured it was worth the risk.

I plugged it right in, with the optical connection, and digital sound
worked immediately with mplayer.  I was a little skeptical about it
really being 5.1, so I played some movies and some test files, and got
distinct sounds outta my surround speakers.  As far as I can tell it's
true 5.1 surround where applicable.  So I set AC3/DTS passthrough in
Myth (not even sure that was necessary), and it works there too.  (And
yes regular stereo PCM works too).

Relevant specs:

Myth 0.20  (ATrpms)
Fedora Core 4, recently updated
ALSA 1.0.12
Chaintech 7NIF2 mobo

The device uses the snd_usb_audio driver, which for me loaded
automatically.  I did read that the AC3 passthrough uses some
proprietary control (you won't see a "setting" in your mixer), but
recent ALSA drivers must have some code that turns it on by default.

Caveat emptor:  This was 2 nights ago, and while I have watched a few
hours of TV, there still could be problems ahead.  Don't take this as
a guarantee, just one man's account.

Now, if I only I could fix one thing, but I think it's an issue with
my a/v receiver:  when skipping around, the audio lags a couple
seconds (it did not do this on my SB analog audio), which I understand
but annoys the wife to no end because you get a second or two of
previous sound with the next part of video.  The audio cues help when
navigating back and forth.  I'm guessing it's because my receiver
takes a sec to start decoding the optical input, but if there's
someway to "mute" for a couple seconds around each skip, that would be
awesome.