Allan Stirling wrote:
Michael T. Dean wrote:
Instead of re-encoding to AC-3, ALSA will allow 6-channel PCM output
via the digital connection.
Not according to:
http://alsa.opensrc.org/SurroundSound
"Note that surround51 and surround40 are supposed to be analog, not
for the digital AC3/DTS. They don't decode anything. They just support
the multi-channel PCM."
Yeah. I know those are analog.
http://www.epanorama.net/documents/audio/spdif.html
"IEC958 was named IEC60958 at 1998. IEC60958 (The S/PDIF) can carry
normal audio and IEC61937 datastreams. IEC61937 datastreams can
contain multichannel sound like MPEG2, AC3 or DTS. When IEC61937
datastrams are transferred, the bits which normally carry audio
samples are replaced with the databits from the datastream and the
headers of the S/PDIF signal. Channel-status information contains one
bit (but 1) which tells if the data in S/PDIF frame is digital audio
or some other data (DTS, AC3, MPEG audio etc.). This bit will tell
normal digital audio equipments that they don't try to play back this
data as they were audio samples. (would sound really horrible if this
happens for some reason)."
So most decoders only support 48kHz @ (max) 24bit x 2 channels.
Dividing this down to get more channels isn't supported AND would
sound nasty.
Hence why AC3, DTS etc is used as the protocol.
OK. I stand corrected. I didn't realize S/PDIF was so limited. I had
seen a lot of info on the 'net talking about multi-channel PCM audio
over S/PDIF, but had never actually tried it myself (having a 2 speaker
setup and all). I may use analog connections instead of digital, after all.
Mike
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