[mythtv-users] 7.1 channel audio

Michael T. Dean mtdean at thirdcontact.com
Sat Mar 10 18:31:42 UTC 2007

On 03/10/2007 11:42 AM, Al McIntosh wrote:
> Michael T. Dean wrote:
>> On 03/10/2007 10:58 AM, Al McIntosh wrote:
>>> Michael T. Dean wrote:
>>>> On 03/09/2007 11:13 PM, Al McIntosh wrote:
>>>>>     I have a Sound Blaster Live! card connected to 7.1 amp via optical 
>>>>> coax cable. When I watch DVDs or anything with xine I get nice, rich 
>>>>> full surround sound. However, when I watch recorded shows within mythtv 
>>>>> there is no output from LS or RS. The front , center and rear channels 
>>>>> all output.   Is this a shortcoming of my current version 
>>>>> *mythtv-0.20-153.fc6.at*? With the below .asoundrc I set playback to 
>>>>> ALSA:default.  Any ideas?
>>>> See the thread:
>>>> http://www.gossamer-threads.com/lists/mythtv/users/134449#134449
>>>> and especially:
>>>> http://www.gossamer-threads.com/lists/mythtv/users/134552#134552
>>> From what I understand, these threads all suggest configuring ALSA to 
>>> duplicate front channel sounds for output to the unused channels. IE: my 
>>> LS and RS channels.
>>> I will still be missing the actual sounds that are intended for LS and 
>>> RS channels.
>> Show me a source you're getting with 7.1 channels (other than 
>> DVD's--which you've said you have working), and I'll mention the other 
>> possible approach (#1104).
> Okay, my AMP can up convert a 5.1 to 7.1, which typically works.

And if you read the (entire) thread I referenced, you'll see that it 
does so using very similar algorithms (although--at least according to 
Franco--doing it yourself with ALSA provides much higher quality audio 
than using the amp's internal "upconvert, and I'm guessing you have the 
same amp he does).

>  IE: 
> when I watch a TV show on TV with my Satalite receiver connected to my 
> AMP via RCA cables, I receive 7.1 channels of audio. If I playback the 
> same show recorded in myth, my LS and RS are as I have mentioned unused. 
> So you're saying I have 2 choices, use ALSA to duplicate channels for 
> playback or compile an #1104  patched version of Myth?  So the 1104 does 
> that also duplicate channels?

Actually, I haven't explained about #1104.  You'd have to write the 7.1 
channel support for it, because it doesn't yet have it--therefore, you 
could decide how to invent the non-existant information (if you have 
some approach that's better than just duplicating channels).


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