[mythtv-users] 7.1 channel audio

Al McIntosh junkmail at allanmcintosh.com
Sun Mar 11 00:11:26 UTC 2007

Michael T. Dean wrote:
> 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).

Right, I see what you're saying. I'll tinker with this and get back.  I 
guess it probably makes more sense to duplicate the rear channels in the 
side  as they're supposed to be background and subtle.  I guess I can 
play and see what sounds better.


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