[mythtv-users] MythMusic spdif only works with some deciders-preamps

[Allen Edwards]

On Thu, Feb 12, 2009 at 4:55 PM, Nick Rout <nick.rout at gmail.com> wrote:
> On Fri, Feb 13, 2009 at 11:10 AM, Allen Edwards
> <allen.p.edwards at gmail.com> wrote:
>> If I play an mp3 file from mythmusic it will play fine through my
>> Technics SH-AC500D decoder which happens to be hooked up to my TV.
>> The other spdif output I have out of the myth box goes to a high end
>> Outlaw 990 decoder-preamp.  There is no output from the 990.  Both the
>> 500D and the 990 switch to non Dolby modes with MythMusic but, like I
>> said, only the 500D decodes it.  When playing a recorded ATSC TV show,
>> which is Dolby Digital, both boxes indicate Dolby D and play fine.
>>
>> Can anyone explain this and let me know if there is a fix?  I could
>> not find anything using google.
>>
>> I actually discovered this with mplayer but thought I would simplify
>> the thread by focusing on mythmusic, but this problem is not only with
>> mythmusic.
>>
>> As a side question, can anyone verify the format that goes out over
>> the spdif port when playing an mp3?  Mythfrontend log says sr 44100 so
>> I assume it is standard pcm 44.1KHz data.  But why won't it decode?
>>
>> Outlaw Audio tech support has never had a call where the 990 could not
>> decode a spdif input so they were not helpful.  They tossed the ball
>> back in my court to find out more about the spdif stream.
>>
>> Any help is appreciated.
>>
>> Allen
>
> Are they being fed by the same soundcard? Some soundcards will pass
> 44.1k, some won't.
>
> AFAIK spdif will send stereo PCM or more channels (certainly 5.1, not
> sure about 7.1) via ac3 or DTS. Your mp3 will be decoded to PCM by
> your player app and then the PCM passed to the receiver (perhaps with
> more processing by alsa).
>
> The spdif specs cover a range of sample rates [1], its just that some
> cards don't handle anything other than 48k. You'll find pretty well
> all video like broadcast TV, DVD's etc use 48k, so they work. CD music
> on the other hand is always 44.1k and this is where it falls down.
>
> At least thats my understanding of it!
>
> Nothing in my post refers to new HD audio techniques, none of which I
> have fully grokked yet.
>
> [1] my logitech z5500 decoder's specs say it supports "PCM
> (uncompressed stereo): 44.1 kHz / 16 bit through 96 kHz / 24 bit" (as
> well as DD and DTS and DTS96/24)
>

Thanks for the reply.

Both spdif outputs come from the MB.  I can switch the cables and it
doesn't change anything.

The processor that does not play (Outlaw 990) is the fancy one, rated
up to 192KHz [1] and it can certainly play 44.1kHz, I just tried it to
make sure.

To simplify things, I used mplayer to play a CD.  It worked fine into
the technics and was silent into the 990, just like MythMusic.  Again,
playing a CD with a CD player works fine with both.

Here is a link to the 990 http://www.outlawaudio.com/products/990.html
New low price ~$700 and competitive with much more expensive units.

[1] AD1896:  192 kHz Stereo Asynchronous Sample Rate Converter
Accepts 16-/18-/20-/24-Bit Data
Up to 192 kHz Sample Rate


Allen