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Thread: Finally: Digital AC-3 surround sound with pulseaudio (aka Surround Sound Awesomeness)

  1. #91
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    Re: Finally: Digital AC-3 surround sound with pulseaudio (aka Surround Sound Awesomen

    That still doesn't change the fact that in Ubuntu 12.04 you cannot select from the correct list of profiles in the sound card. Thus, it's a bug with no solution thus far.

    So either way it's still a question of how do I select "Digital Output 5.1 Surround Sound" like I used to in 11.04/11.10 since that functionality was (see this bug report https://bugs.launchpad.net/ubuntu/+s...er/+bug/972554), more or less, taken away?

    Even though >pacmd lists all the correct profiles including digital surround sound?

  2. #92
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    Ubuntu 10.04 Lucid Lynx

    Re: Finally: Digital AC-3 surround sound with pulseaudio (aka Surround Sound Awesomen

    So they made the gnome sound more crap (in 12.04) than it already was..

    Can you try pavucontrol ?

    The main guts of this thread was never about using alsa a52 plugin with pulse-audio, misleading thread title excepted...
    If pulse enumerated & worked with the alsa a52 plugin is was good luck..

    Does the alsa device surround51 still show up ?
    You can redefine the surround51 to output to the a52 plugin:
    Code:
    #/etc/asound.conf
    # speaker-test -c 6 -r 48000 -D surround51
    pcm.!surround51 {
       @args.0 SLAVE
       @args.SLAVE {
                   type string
                   default "a52"
       }
       type route
       slave {
             pcm $SLAVE
             channels 6
       }
       ttable {
         0.0= 1
         1.1= 1
         2.2= 1
         3.3= 1
         4.4= 1
         5.5= 1
       }
    }
    Last edited by BicyclerBoy; April 30th, 2012 at 08:49 PM.

  3. #93
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    Re: Finally: Digital AC-3 surround sound with pulseaudio (aka Surround Sound Awesomen

    Quote Originally Posted by BicyclerBoy View Post
    The common use of S/PDIF does not require a52 plugin..
    Once pulse-audio sorts itself out, pass-thru will be possible thru' the system wide audio setup. But it will be exclusive access.

    S/PDIF stereo PCM is not encoded, it is lossless PCM digital a bit like serialised WAV file..

    The a52 AC3 encoder is non-free.
    Is has application for multi-channel audio if you don't have a HDMI AVR & maybe for gaming. So not that useful.
    Up-mixing everything to 5.1 must be a personal preference..

    Digital pass-thru' is not trivial to get working. The application or plugin must have exclusive access/control. This would make it system wide.
    Then a media player would have to decode everything to multi-channel PCM just for the a52 to encode & HT amp to decode.
    This method allows system sounds (full sharing of audio output).

    The alsa a52 plugin releases iec958 when it is not encoding.
    Another way is to point applications at appropriate audio device.

    I use digital pass-thru' on a per-application basis.
    Stereo & pass thru' for HTPC (default iec958) & upsampled stereo PCM for audio (custom iec958_24_96K).

    The a52 encode AQ is questionable, I prefer to use a52/DTS decoder in amp.
    I don't want DTS/AC3/DTS-MA etc to be decoded in PC.

    The one good thing about the alsa a52 plugin is the ability to dmix (share & control volume).

    Volume control can be done over HDMI with CEC or multi-channel LPCM
    I tried to ignore your misconceptions but I feel I must clarify a few things.

    I never said spdif requires the a52 plugin. I said we could encode audio sources via the a52 plugin for surround sound playback (make it a selectable sound sink). There would still be stereo pcm for quality and pass-through available for relavent sources.

    Stereo PCM (pulse code modulation) is encoded. I did not say it was encrypted or compressed. Its called a format. A format is a code. Raw bits [streams] are virtually useless, unless interpreted in some way. The receiver and sender must both know the meaning of the bits.

    Digital pass-through implies the data source is sent to the hardware interface untouched. The source is pre-encoded in formats (ac3,dts etc) the receiver can decode. A [pc] media player cannot decode digital pass-through. That does not even make sense! Digital pass-through is not a source. A media player can decode the ac3 stream.

    The a52 AC3 encoder is free (see http://liba52.sourceforge.net/) having been released under GPL although it may be restricted. The a52 plugin encodes audio channels to AC-3, and sends the data by the spdif/toslink interface to the receiver to be decoded.

  4. #94
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    Re: Finally: Digital AC-3 surround sound with pulseaudio (aka Surround Sound Awesomen

    "usage of S/PDIF requires a52 plugin" ..I never said that either.

    When all is working (alsa a52 plug, pulse etc) then you can select the a52 plug as an output device along side others..

    Is is a selectable audio sink..

    Are you suggesting that the a52 plugin is automatically available to all audio applications to use as they need it ? i.e PCM or a52 or pass-thru'?
    Because that makes good sense..

    The a52 does not get a lot of testing because;
    - until recently pulse audio did not support pass-thru'
    - no one uses it.
    - the a52 plug is not shipped with ubuntu, if it were free it would be.
    - a52 depends on libavcodec & is broken often.
    - pulse is often broken by enumerating a52 plug device.
    - vlc mythtv XBMC can use an internal a52 encoder.
    - HDMI has made it history/obsolete/deprecated.

    I know that in the strictest terms PCM is encoded but in the context of AV codecs it is raw data in a simple frame.
    The words matrix encoded multi-channel are in there somewhere.
    The S/PDIF PCM 'encoding' is trivial & done by the audio codec. a52 encoding is avail on some expensive discrete soundcards but here the encoding is still normally performed by software (soundcard driver).

    I never said the media player etc would be decoding pass-thru' bitstream..
    That's your interpretation..
    I know what digital pass-thru' is.

    Using a52 plugin for all multi-channel audio would mean that playback results in 2 decoding steps & 1 encoding step; only one is bug free (hopefully).

    Sorry if I had misunderstood your comments but I still believe what I have stated is correct in context & in implied meaning.

    Use of the a52 encoder is not free & unrestricted.
    Last edited by BicyclerBoy; May 1st, 2012 at 02:41 AM.

  5. #95
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    Post Re: Finally: Digital AC-3 surround sound with pulseaudio (aka Surround Sound Awesomen

    Quote Originally Posted by BicyclerBoy View Post
    "usage of S/PDIF requires a52 plugin" ..I never said that either.

    When all is working (alsa a52 plug, pulse etc) then you can select the a52 plug as an output device along side others..

    Is is a selectable audio sink..

    Are you suggesting that the a52 plugin is automatically available to all audio applications to use as they need it ? i.e PCM or a52 or pass-thru'?
    Because that makes good sense..

    The a52 does not get a lot of testing because;
    - until recently pulse audio did not support pass-thru'
    - no one uses it.
    - the a52 plug is not shipped with ubuntu, if it were free it would be.
    - a52 depends on libavcodec & is broken often.
    - pulse is often broken by enumerating a52 plug device.
    - vlc mythtv XBMC can use an internal a52 encoder.
    - HDMI has made it history/obsolete/deprecated.

    I know that in the strictest terms PCM is encoded but in the context of AV codecs it is raw data in a simple frame.
    The words matrix encoded multi-channel are in there somewhere.
    The S/PDIF PCM 'encoding' is trivial & done by the audio codec. a52 encoding is avail on some expensive discrete soundcards but here the encoding is still normally performed by software (soundcard driver).

    I never said the media player etc would be decoding pass-thru' bitstream..
    That's your interpretation..
    I know what digital pass-thru' is.

    Using a52 plugin for all multi-channel audio would mean that playback results in 2 decoding steps & 1 encoding step; only one is bug free (hopefully).

    Sorry if I had misunderstood your comments but I still believe what I have stated is correct in context & in implied meaning.

    Use of the a52 encoder is not free & unrestricted.
    I won't waste my time time anymore. For those interested http://ac3filter.net/wiki/AC3Filter_...s_handle_SPDIF is a good explanation on the topic:

  6. #96
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    Re: Finally: Digital AC-3 surround sound with pulseaudio (aka Surround Sound Awesomen

    @ terran4000
    pulse in 12.04 supports pass-thru' & the a52 plugin.

    Install/run pavucontrol, forget the gnome volume control..

    If the a52 alsa plugin is enumerated then the plug will be listed in the [configuration] tab.

    [configuration]
    - (1) Digital Stereo (IEC958) Output
    - (2) Digital Surround 5.1 (IEC958/AC3) Output

    [Output Devices]
    - if (1) then choose pass-thru options AC3 DTS EAC3 MPEG
    - if (2) adjust volume mix..

    (1) is for stereo PCM & pass-thru' (media player must support)
    (2) 6 ch PCM encoded to 5.1AC3/A52.

    Note: (1) pass-thru can not be shared/dmixed.

    An alternative a52 plugin build process for 12.04 64bit:
    #get alsa-plugins-1.0.25.tar.gz from alsa-project.org
    #extract to folder..

    cd alsa/alsa-plugins-1.0.25/
    ./configure
    # check the a52 plug is enabled etc..
    make -j4
    cd a52/.libs
    sudo cp libasound_module_pcm_a52.la libasound_module_pcm_a52.so /usr/lib/x86_64-linux-gnu/alsa-lib/

    sudo gedit /etc/asound.conf
    Code:
    # /etc/asound.conf
    # alsa plugin a52
    # speaker-test -c 6 -l 1 -D pcm.a52:[CARD]
    pcm.a52 {
      @args [CARD]
      @args.CARD {
        type string
      }
      type rate
      slave {
        pcm {
          type a52
          bitrate 640 # 448 is max for most
          channels 6
          card $CARD
        }
      rate 48000
      }
    }
    sudo alsa reload
    killall pulseaudio

    sudo apt-get install pavucontrol

    References:
    https://help.ubuntu.com/community/DigitalAC-3Pulseaudio
    http://www.alsa-project.org/main/index.php/Main_Page
    Last edited by BicyclerBoy; May 2nd, 2012 at 09:06 PM.

  7. #97
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    Re: Finally: Digital AC-3 surround sound with pulseaudio (aka Surround Sound Awesomen

    Woot! @BicyclerBoy thanks the reminder n' stuff. Well, whatever update there was recently in 12.04 (there were several updates already) "Digital Surround 5.1 (IEC958/AC3) Output" shows up finally in pavucontrol in the Configuration tab!

    Thanks for pointing that one out. Guess I just kept looking at the wrong place, because I did check pavucontrol before and didn't notice it there in 12.04 before.

    Either way, thanks BicyclerBoy! Saved my ears!

    Quote Originally Posted by BicyclerBoy View Post
    @ terran4000
    pulse in 12.04 supports pass-thru' & the a52 plugin.

    Install/run pavucontrol, forget the gnome volume control..

    If the a52 alsa plugin is enumerated then the plug will be listed in the [configuration] tab.

    [configuration]
    - (1) Digital Stereo (IEC958) Output
    - (2) Digital Surround 5.1 (IEC958/AC3) Output

    [Output Devices]
    - if (1) then choose pass-thru options AC3 DTS EAC3 MPEG
    - if (2) adjust volume mix..

    (1) is for stereo PCM & pass-thru' (media player must support)
    (2) 6 ch PCM encoded to 5.1AC3/A52.

    Note: (1) pass-thru can not be shared/dmixed.

    An alternative a52 plugin build process for 12.04 64bit:
    #get alsa-plugins-1.0.25.tar.gz from alsa-project.org
    #extract to folder..

    cd alsa/alsa-plugins-1.0.25/
    ./configure
    # check the a52 plug is enabled etc..
    make -j4
    cd a52/.libs
    sudo cp libasound_module_pcm_a52.la libasound_module_pcm_a52.so /usr/lib/x86_64-linux-gnu/alsa-lib/

    sudo gedit /etc/asound.conf
    Code:
    # /etc/asound.conf
    # alsa plugin a52
    # speaker-test -c 6 -l 1 -D pcm.a52:[CARD]
    pcm.a52 {
      @args [CARD]
      @args.CARD {
        type string
      }
      type rate
      slave {
        pcm {
          type a52
          bitrate 640 # 448 is max for most
          channels 6
          card $CARD
        }
      rate 48000
      }
    }
    sudo alsa reload
    killall pulseaudio

    sudo apt-get install pavucontrol

    References:
    https://help.ubuntu.com/community/DigitalAC-3Pulseaudio
    http://www.alsa-project.org/main/index.php/Main_Page

  8. #98
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    May 2012
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    1

    Re: Finally: Digital AC-3 surround sound with pulseaudio (aka Surround Sound Awesomen

    Hi

    With your help I am able to select the Digital surround sound profile and the sound works correctly for a period but then crashes. I am unsure how to diagnose the problem. Looking online people were suggesting it was my asound.conf but it is the same as in this thread. Any ideas?

    THanks

  9. #99
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    Mar 2009
    Location
    San Diego, CA
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    Ubuntu 10.04 Lucid Lynx

    Re: Finally: Digital AC-3 surround sound with pulseaudio (aka Surround Sound Awesomen

    Would anyone know why this stops working properly after suspending and resuming the computer? Any ideas on a workaround or fix to stop it from doing so?

    I'm running 11.10 and using this to enable me to play surround sound through my receiver.

  10. #100
    Join Date
    Jun 2009
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    3

    Re: Finally: Digital AC-3 surround sound with pulseaudio (aka Surround Sound Awesomen

    the ubuntu 12.04 steps works, if you haven't done any other steps you need to install 2 packages before starting:


    sudo apt-get install libasound2-dev libavcodec-dev

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