[mythtv-users] Digital Audio Problems - Noisey, stuttering, skipping

Mike Smith easygreenus at yahoo.com
Mon Jan 19 22:08:15 UTC 2009


Sorry for the weird description.  Machine gun like doesn't sound very technical.

Using Fedora 10.

I'm building a new Mythfrontend box in preparation for capturing HD.  I have a
Gigabyte motherboard that uses the Nvidia 9400 chip set.  It uses the Realtek
ALC889A chipset.  Interesting board for HDTV, if I can get it all working.
It have VGA, VDI, and HDMI outputs to connect to the TV.

For audio,  it has an optical SPDIF that I am trying to use.  I have connected
an optical cable to it.  

bash-3.2$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: NVidia [HDA NVidia], device 0: ALC883 Analog [ALC883 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 1: ALC883 Digital [ALC883 Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 3: NVIDIA HDMI [NVIDIA HDMI]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
bash-3.2$ 
bash-3.2$ 
bash-3.2$ aplay -L
front:CARD=NVidia,DEV=0
    HDA NVidia, ALC883 Analog
    Front speakers
surround40:CARD=NVidia,DEV=0
    HDA NVidia, ALC883 Analog
    4.0 Surround output to Front and Rear speakers
surround41:CARD=NVidia,DEV=0
    HDA NVidia, ALC883 Analog
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=NVidia,DEV=0
    HDA NVidia, ALC883 Analog
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=NVidia,DEV=0
    HDA NVidia, ALC883 Analog
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=NVidia,DEV=0
    HDA NVidia, ALC883 Analog
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=NVidia,DEV=0
    HDA NVidia, ALC883 Digital
    IEC958 (S/PDIF) Digital Audio Output
null
    Discard all samples (playback) or generate zero samples (capture)
pulse
    PulseAudio Sound Server
default
    Default

I followed the steps Mythtv Wiki article 

Configuring Digital Sound with AC3 and SPDIF
and


Configuring Digital Sound
I have configured the alsamixer and checked the iec958 and iec958 Default PCM boxes 
and can see the laser light come on ( pointed at some white paper, of course. )

I downloaded an ac3 file called Prelude.wav from the net and ran:

bash-3.2$ aplay -D iec958 Prelude.wav 
Playing WAVE 'Prelude.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo

Music plays fine and the DTS light on my receiver goes on.

I downloaded some music tracks that that are .ac3 and they all play fine.

I also ran the speaker test recommended:

bash-3.2$ speaker-test -c6 -t wav

speaker-test 1.0.18

Playback device is default
Stream parameters are 48000Hz, S16_LE, 6 channels
WAV file(s)
Rate set to 48000Hz (requested 48000Hz)
Buffer size range from 32 to 349525
Period size range from 10 to 116509
Using max buffer size 349524
Periods = 4
was set period_size = 87381
was set buffer_size = 349524
 0 - Front Left
 4 - Center
 1 - Front Right
 3 - Rear Right
 2 - Rear Left

It worked, and the DTS light comes up on my receiver.

I go into the mythtv sound setup.  Its the third screen under
"General".

Audio Output Device - Alsa:Default
Passthru Output Device - Default
Max Audio Channels 5.1
Checked "Enable AC3 to SPDIF Passthrough"
Checked "Enable DTS to SPDIF Passthrough"
Checked "Use Internal Volume Controls"
Mixer Device - Alsa:Default
Mixer Controls - Master


I can play my Programs that were captured using MythTV.  They are going through
the Optical SPDIF, but they are captured in Analog stereo.

Its the DVDs that I have ripped that have the sound like machine gun fire.
I ripped a new one last night with the AC3 capture checked.  Same problem.

Anyone have any ideas?


Thanks,


Mike



      


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