[LAU] can't do 5.1 audio from a PC!
florin at andrei.myip.org
Fri Nov 14 15:02:29 EST 2008
Clemens Ladisch wrote:
> Florin Andrei wrote:
>> But with the PC, once the digital coaxial carrier comes up, it's always
>> ProLogic and 2.1, never Dolby Digital and 5.1
> SPDIF was designed for stereo, so it has only the bandwidth for two
> channels of data at 48 kHz. (There are extensions for higher sample
> rates by increasing the clock, but there are never more than two
> To transport more than two channels over SPDIF, the audio data has to
> be compressed so that it fits into the bandwidth that two uncompressed
> channels would use. There are two common codecs, Dolby/AC-3 and DTS;
> both are heavily patented.
> Any sound card that wants to encode multichannel audio for transport
> over SPDIF has to include an encoder license. Very few do (the Windows
> drivers for CMI8768+/8770/8788 and some X-Fi cards come with encoders).
> Without encoder, 5.1 playback works only when the source data has
> already been encoded previously (e.g., on a DVD).
Awesome - that clarifies some things I discovered last night when
googling around and doing experiments with the motherboard.
The consensus seems to be it's very hard to do 5.1 over S/PDIF unless
the data is already encoded like that (DVD) - you provided the
explanation for that. So, if I play a DVD it might be doable, but if I
play a game that has capabilities for 5.1 output, most likely it will
What I discovered is that the sound chip on the mobo can send 5 audio
channels over analog. I guess that should remove all limitations, isn't it?
> AFAIK there is no Linux distribution that ships with an encoder,
> but you can download and install an AC-3 encoder manually (see
Is there anything similar for Windows? Some sort of universal plugin
that works with any card?
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