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| Digital sound from myth - confused http://forum.linhes.org/viewtopic.php?f=17&t=15452 |
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| Author: | ffrr [ Fri Jun 01, 2007 9:12 pm ] |
| Post subject: | Digital sound from myth - confused |
I have changed my old SBLive to a SB Audigy SE (uses the CA0106 chip) with the external digital I/O module. I am running Knoppmyth R5E50. I have searched and read a lot of stuff, but it gets confusing, especially when you have to sort out what is out of date etc. So, bear with me, and maybe you can help me sort it out. I had analog sound from the SBLive working fine, but I can't get the Audigy to output anything analog, HOWEVER, luckily, I am getting digital out. To get digital out working I changed the passthrough device in mythfrontend setup?general, from default to the IEC 958 option, and I left the main sound output set to /dev/dsp I ran alsamixer and found I had to unmute it, and increase the 'front' IEC958 channel level up from zero. None of the others seem to make any difference. It may be that the recorded TV (from DVB-T cards) only has 2 channels. My receiver indicates it is getting a digital stream, and derives decent surround sound from it using pro-logic II, but it's not 5.1 sound (nor DTS). Some questions then, 1) How do I save these alsamixer settings - they seem to need to be redone after a reboot? 2) How do I get mythtv to control the volume of the digital sound? It seems to ignore the '[' and ']' key control when playing back. The screen shows the volume changing, but the actual sound levels don't change. 3) Does what I described - with the IEC858 front channel control being the only active one, sound correct? If I record material with true 5.1 or DTS, will that cause the others (centre, rear etc) to be active? 4) When I tick the AC3 and DTS passthrough checkboxes in mythfrontend setup, some recordings make a nasty static noise when I play them back, and others play OK. Is this normal? I did read one post that this happens when an AC3 or DTS track doesn't exist. Also that it would be fixed in myth 0.19? 5) I read some promising looking instructions here http://www.mythtv.org/wiki/index.php/Co ... ital_Sound about creating a /etc/asound.conf file. Knoppmyth doesn't seem to have one, so is it safe to do this in Knoppmyth (and will it work) ? |
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| Author: | ffrr [ Sun Jun 03, 2007 5:16 pm ] |
| Post subject: | |
I have been pursuing this over the weekend, and so, I wanted to update this question with what I have found/done so far. I found out about the "alsactl store" command to save the mixer settings I discovered I can get good digital sound, even passthrough all working using "ALSA:spdif" in place of "/dev/dsp". I didn't realise that you can type in these other things, I though you were limited to what the arrow keys let you choose, and /dev/adsp didn't work. With "ALSA:spdif" chosen as the output, and "default" as the passthrough (and both checkboxes selected) I get digital sound for all my recordings. My next steps will be to try other things, such as playing MP3's and DVDs. I suspect I will need, at least, a rudimentary asound.conf. Of course, any tips and advice to help me along the way, would be appreciated. |
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| Author: | Girkers [ Sun Jun 03, 2007 9:48 pm ] |
| Post subject: | |
With DVDs if you are using the internal player (I don't think 0.19 had that) it will use your current settings. If you are using Xine to play DVDs you will have to edit the config file in /home/mythtv/.xine From the xine FAQ: Quote: Setting up xine for SPDIF (AC3 passthrough) output
You can either use the config dialog of your frontend or edit the config file (~/.xine/config) yourself: audio.output.speaker_arrangement:Pass Through In case the setting is not in the file you can add it. Reference: http://xinehq.de/index.php/faq |
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