alien9999999
Your Head Looks Nice
Premium
join:2002-05-21
B-3000
|  Optical Audio IN mixing with PCM into optical out
I have a device that has optical out (toslink), i also have a speakerset that does optical in (toslink).
I have a server with a mythbox on it.
I plan to buy an audio card with optical in and optical out. so i can plug in the device and the speaker set.
The question is: Can i mix the optical in and whatever comes from PCM(pc applications) to the optical out? and will that have additional CPU load?
I'm on linux, and i just need to know if it is possible.
I'm just thinking that theorethically, the soundcard has raw optical in (or AC3), and the optical out has the same format. i wonder if the soundcard can mix that with whatever comes from PCM (hopefully AC3 as well, but not always), without converting to analog...
I fear that the PCM would have to be upmixed, and maybe the AC3 would need to be decoded in software and mixed with PCM.
Can anyone help me with this question.
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Alien is my name and headbiting is my game. |
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yock
TFTC
Premium
join:2000-11-21
Fairfield, OH
| We can speak in generalities all day, but that doesn't really help you. What you're asking for isn't complicated, but will depend on the capabilities of the specific sound card.
Obviously, you'll want a sound card that can attach to all of your devices in the best possible format. If you can go optical to the surround, then that's what you want to do. Theoretically, the cound card would do all of the mixing. Passing surround signals wouldn't be a problem, but it could also replicate a simple stereo signal to all channels on the destination device.
It will just depend on the sound card. |
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russotto
join:2000-10-05
Collegeville, PA
| reply to alien9999999
I'm not aware of any linux application which can mix to AC3 on the digital output. You can decode the AC3 and mix with anything else, but you can't get better than stereo out. Or you can pass the AC3 through unchanged.
There is a linux program called 'aften' which can create AC3 streams, but I do not believe it is capable of doing so in real time. |
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Vchat20
Landing is the REAL challenge
join:2003-09-16
Warren, OH
clubs: 
| said by russotto  :I'm not aware of any linux application which can mix to AC3 on the digital output. You can decode the AC3 and mix with anything else, but you can't get better than stereo out. Or you can pass the AC3 through unchanged. There is a linux program called 'aften' which can create AC3 streams, but I do not believe it is capable of doing so in real time. Quoted for fact.
There currently are no applications that can mix/encode AC3 on the fly and keep a low delay (as which is needed in many cases).
Now if you are only worried about stereo audio, you can simply stick to PCM audio which is computationally a piece of cake to decode, mix, and output on the fly.
For surround sound though, you can only run AC3 over a coaxial or optical connection due to bandwidth limitations. And as stated above, there's no way to decode, mix, and encode AC3 on the fly and with low delay in software. Though you can certainly output an existing AC3 stream directly over that connection with no problem.
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I swear, some people should have pace-makers installed to free up the resources. Breathing and heart beat taxes their whole system, all of their brain cells wasted on life support.-two bit brains, and the second bit is wasted on parity! ~head_spaz |
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alien9999999
Your Head Looks Nice
Premium
join:2002-05-21
B-3000
| i see.
so, i cannot upmix stereo sound from a divX to AC3 for instance?
Will i have to change settings on my speakers, or something?
I've seen this card: »www.alternate.be/html/product/de···ata=true
would this do the trick, or is it impossible to say? i've also looked at Creative, but they are expensive: »be-nl.europe.creative.com/produc···&listby=
What do you think?
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Alien is my name and headbiting is my game. |
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yock
TFTC
Premium
join:2000-11-21
Fairfield, OH
| said by alien9999999 :so, i cannot upmix stereo sound from a divX to AC3 for instance? You can't durn non-positional audio into positional audio, but you should be able to replicate the stereo signal across all channels, depending on your sound card and accompanying software. |
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alien9999999
Your Head Looks Nice
Premium
join:2002-05-21
B-3000 | what do you think about the 2 links i posted? which is a good soundcard?
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Alien is my name and headbiting is my game. |
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russotto
join:2000-10-05
Collegeville, PA
| reply to alien9999999
If it's the optical out you are using, the quality of the soundcard isn't particularly important, as long as it isn't actually broken and Linux supports it.
If you wanted to replicate the stereo signal from the optical out across all channels, you'd have to do that at the speakerset.
If you're going to be using the analog surround outputs on the sound card, you can do all the mixing you want. |
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alien9999999
Your Head Looks Nice
Premium
join:2002-05-21
B-3000
| reply to alien9999999
what i really want is the following:
preferably without changing any setting, ie: play from PC or play from sounddevice. If at all possible, i'd like both.
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Alien is my name and headbiting is my game. |
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Vchat20
Landing is the REAL challenge
join:2003-09-16
Warren, OH
clubs:
| reply to alien9999999
Like has been said already: You cannot mix multiple sources and keep producing a surround feed because you absolutely MUST use AC3 for anything above stereo audio and there is no current software to encode AC3 on the fly because it is so computationally expensive.
That being said, in your earlier example of stereo audio from a divx movie, you could certainly output that as PCM to your receiver in stereo (or direct AC3 if the audio in the divx file is as such) and let your receiver upsample it to surround.
And like another poster had said: The quality of the sound card is not important really as long as the optical/coaxial inputs and outputs you desire are there and working and linux supports it. When using digital audio, 90% of the workload and quality considerations fall on the software you are running.
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I swear, some people should have pace-makers installed to free up the resources. Breathing and heart beat taxes their whole system, all of their brain cells wasted on life support.-two bit brains, and the second bit is wasted on parity! ~head_spaz |
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russotto
join:2000-10-05
Collegeville, PA
| reply to alien9999999
said by alien9999999 :what i really want is the following: Possible with stereo output, NOT possible with surround output. |
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