[mythtv-users] mythmusic iec958 help

Richard Shaw hobbes1069 at gmail.com
Sun Jul 6 13:13:28 UTC 2008


On Sun, Jul 6, 2008 at 12:35 AM, Alen Edwards
<allen.edwards at oldpaloalto.com> wrote:
> Rich West wrote:
>> Joe Henley wrote:
>>> Gregg,
>>>
>>>  From the posts above it doesn't look like it's going too well.  I
>>> continue to believe you will need to replace your sound card if you want
>>> to get 44.1KHz signals into your receiver.
>>>
>>> Have you checked the SoundBlaster site (or googled) for clarification on
>>> what your specific card will do?  Allen's comments above about
>>> "sometimes spdif means upto 48KHz" is not 100%.  Sometimes it's 48KHz
>>> only; trust me, been there, done that.  ... and paid the return shipping
>>> for a limited capability card.
>>>
>>> If your Soundblaster is not designed to output 44.1KHz via spdif, no
>>> tweaking of alsa parameters, etc. will help.
>>>
>>> If your particular SB model will support 44.1KHz, then remove .asoundrc
>>> from /root , /home, and /etc, and anywhere else it resides.  IIRC, you
>>> have already removed PukeAudio, so from there you can start using
>>> alsamixer to unmute the iec958 items.
>>>
>>> The most common (from what I read on sites like this) successful MythTV
>>> settings are:
>>> Audio output device =  ALSA: spdif
>>> Passthru output device = Default
>>> Max audio channels = stereo (The 5.1 setting is currently broken. Use
>>> "stereo" and you'll still get 5.1 sound out of the system.)
>>> Upmix = passive
>>> Enable AC3 to SPDIF passthru = check
>>> Enable DTS to SPDIF passthru = check
>>> Enable internal volume controls = check
>>> Mixer device = default
>>> Mixer controls = Master
>>>
>>> What will work for you is probably very similar to this.  If this
>>> doesn't work first time, then check the wiki for ways to determine good
>>> alternatives to "Audio output device = ALSA: spdif".  This setting seems
>>> to have several different incantations; and seems to be the one most
>>> people have to change.
>>>
>>> Good luch, you _will_ eventually succeed,
>> For more information, check out:
>> http://www.mythtv.org/wiki/index.php/Configuring_Digital_Sound_with_AC3_and_SPDIF
>>
>> That page will walk you through what steps to take to:
>> o get spdif sound working with linux (Fedora) - something you already
>> have working
>> o get the configuration set up to work with Myth (and MythVideo) for 5.1
>> and stereo output - something you already have working
>> o and get the configuration set up to work with MythMusic - the piece
>> you are trying to get working
>>
>> More than likely, you're using a system with on-board SPDIF 5.1
>> surround.. if that is the case, then it should be able to be done (and
>> if it is AC97 chipset based, it is definitely possible).
>>
>> The key piece to get MythMusic working when you have all of the other
>> components working is by setting "Max audio channels = stereo".
>>
>> -Rich
>
> That wiki is good.
> Just don't get distracted with this one:
> http://www.mythtv.org/wiki/index.php/Configuring_Digital_Sound
> It doesn't work.
>
> Allen

I hope I'm not hijacking this thread too much but I have been
following all of these sound/spdif/iec958 threads and I've gotten
myself more educated on this with the side effect of getting more
confused as well... I've read every wiki I could find (both Mythtv
ones and the alsa one) I think a lot of the info may be slightly old.
For instance, no matter what I do the output of aplay -L is:

[root at calvin ~]# aplay -L
front:CARD=CK8S,DEV=0
    NVidia CK8S, NVidia CK8S
    Front speakers
surround40:CARD=CK8S,DEV=0
    NVidia CK8S, NVidia CK8S
    4.0 Surround output to Front and Rear speakers
surround41:CARD=CK8S,DEV=0
    NVidia CK8S, NVidia CK8S
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=CK8S,DEV=0
    NVidia CK8S, NVidia CK8S
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=CK8S,DEV=0
    NVidia CK8S, NVidia CK8S
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
null
    Discard all samples (playback) or generate zero samples (capture)
---

The only thing I have found that effects the above output is to edit
/etc/alsa/alsa.conf and turn on the two options that are off
(something about simple names and extended info).

I have no idea what got things working for me again but I did the
"alsactl names" to generate a /etc/asound.names file. I'm not sure if
this actually does anything and I noticed that this option is
depreciated in the help.

I think I *MIGHT* have 44.1kHz working in mythmusic with a nForce
chipset but the conversion to 48kHz may be happening somewhere else...

mythfrontend settings:
Default audio device: ALSA:plug:spdif:0 (from asound.names)
Passthough device: ALSA:iec958{AES0=0x02}
both AC3/DTS checked,
2 channels.

section of mythfrontend log:
---
2008-07-05 21:37:44.739 Opening audio device 'plug:spdif:0'. ch 2(2) sr 44100
2008-07-05 21:37:44.740 Opening ALSA audio device 'plug:spdif:0'.
MMX detected. Using fast method !
---

Another thing that bothers me is that myth uses IEC958 w/ AES0=0x02
but Xine uses AES0=0x06 (verified with iecset -x when both are playing
back a DVD), both of which are "non-audio" and a sample rate of 48kHz
which I assume means that the stream is not meant to be processed but
just passed along...

I'm sure I'm forgetting something as I stayed up too late last night
trying things and the only thing holding me up is my morning coffee...

I would still like to get both analog and digital output
simultaneously at some point but I think I'm going to give up for now
so my wife doesn't kill me.

Richard


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