[mythtv-users] mythmusic iec958 help

Richard Shaw hobbes1069 at gmail.com
Sun Jul 6 21:20:47 UTC 2008


On Sun, Jul 6, 2008 at 8:22 AM, Mark Greenwood <fatgerman at ntlworld.com> wrote:
> On Sunday 06 July 2008 14:13:28 Richard Shaw wrote:
>> 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.
>
> I'm not sure if I'm understanding the problem correctly, but I'm using a Creative USB sound card which has both analogue and optical outputs. The optical output is connected to my surround processor. All I did was to leave myth set to use ALSA:default as its output and enable pass-through for AC3 and DTS, and I get 5.1 surround out of the optical output (assuming I'm playing a DVD. If I'm watching TV I get stereo). I haven't checked to see if any resampling is ocurring, but it doesn't matter - it just works. If I set myth to use the iec958 option, I get nothing at all. Have you tried just using ALSA:default? Or have you tried using an alternative sound card? USB cards with optical I/O are very cheap these days.
>
> Mark
>
Well, I was a little tired this morning so I may not have been to
coherent. The two things I really want is simultaneous analog and
digital output. I'm really tired of leaving the receiver on all the
time just to watch TV when the speakers built into the TV would be
good enough. The other thing I want is bit perfect audio, and since I
have no budget for new gadgets, I want to do everything I can to get
it with my nForce chipset. I may be asking too much...

Even though I had everything working (all digital out) using the
asound.conf from the wiki one consequence was that alsa mixer had no
effect, which I thought was strange and as an engineer I couldn't
accept that :) It was really weird, I could mute/unmute the iec958 and
it didn't mute the audio...

A third thing I really want is consistency... mythmusic was MUCH
louder than other audio and then there is mplayer in the mix for AVI
files.

RIchard


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