Idea
#6148: Make 4.1 (and more) sound over optical cable work better
|
| |
87
|
|
|
Written by Auzy the 31 Mar 08 at 09:23.
Category: Multimedia.
Related to:
Nothing/Others.
Status: New
|
|
|
Description
There is currently no possible open source means of properly playing more then a left and right channel by optical cable on speakers. The problem is that to send more channels, we need Dolby digital, DTS, or WMA Pro, none of which we can legally support without paying for licensing (no thanks), and using closed sourced code.
If we expect to attract gamers or anyone who has more then 2 speakers, we need to encourage the development of an open standard. In the long run, this benefits everyone (except Dolby Labs) because anyone could make compatible decoders and speakers without coughing up money for licensing. It also allows us to add support to Linux without closed source dodginess. Canonical could get the ball rolling by suggesting the idea to Ogg Vorbis, and other audio organisations who may support it.
Most decoders do support upscaling from 2.0 to 5.1, but it never sounds right for gaming. And its not true 5.1. Plus, who wants to buy a high end decoder, and not fully utilise it for gaming?
Tags:
(none)
Attachments
No attachments.
Duplicates
Comments
|
Eldmannen wrote on the 31 Mar 08 at 09:47
|
Interesting idea.
You mean Xiph.Org Foundation though, they're the people who created Ogg Vorbis.
|
|
Auzy wrote on the 31 Mar 08 at 10:03
|
yeah, Xiph, and whoever makes flac, and any of those open source audio guys.. You'd probably also want driver coders too involved, even though the end product would probably be one clean audio library.
Shouldn't be too hard anyway to come up with a protocol, because i don't imagine you would send the streams to the decoder compressed anyway (because you would need to be able to guarentee that there is consistantly enough bandwidth anyway, otherwise you are heading for disaster. So its just a matter of transmitting a basic header with quality information, number of channels, and determining how the raw data is sent (easy)
|
|
ubuntu_demon wrote on the 31 Mar 08 at 11:09
|
I don't know whether this helps. But maybe this part of
http://en.wikipedia.org/wiki/HDTV is interesting :
[quote]
...
Brasil opted to upgrade the ISDB-T Japanese standard to H.264 AVC Mpeg4 part 10 in the video compression and HE-AAC for audio compression because Dolby is not open and the royalty fees are more expensive than that of Mpeg4 H.264 AVC and renamed the upgraded standard to ISDB-Tb that now became the International ISDB-T standard.
...
[/quote]
|
|
Auzy wrote on the 31 Mar 08 at 11:17
|
Problem is demon, to make hardware as cheap as possible, we want a raw stream (without any quality loss).. HE-AAC is lossy.
Decoding a raw stream doesn't take very complicated hardware to decode, or software to encode.
And we need to guarentee that sound that cannot be compressed can be sent without quality loss. If we need to compress the sound to get it to the speakers, it means that the moment the compression ratio is 0%, we lose quality.
Keep it simple, and people will adopt it. And keep it simple, and you could have a standard which is less then a few pages, that does everything we want, and will last a VERY long time. If its simple enough, even the hardware would be basic, and make it easy to accellerate
|
|
derick.eisenhardt wrote on the 31 Mar 08 at 14:33
| |
I know Ogg Vorbis already supports 5.1 (even 7.1 probably), so if this problem is even real it probably lies with ALSA or sound card drivers. I wonder if the newly GPL'd OSS4 supports multichannel audio output properly...?
|
|
brokencrystal wrote on the 1 Apr 08 at 00:51
| |
Interesting, I was just thinking about this problem the other day...
|
|
Auzy wrote on the 1 Apr 08 at 01:10
|
Maybe I have to explain a bit better.. The process works
ALSA probably supports 5.1 and even 33.1 sound by analog cables, because no decoding is needed on the other end. That we can legally do. Its just like playing over a few headphone jacks. Its 1 speaker, per cable. No tricks needed
The issue lies with optical though.
Analog cable
Cable 1: [sound (analog, L speaker)]
Cable 2: [sound (analog, R speaker)]
However, with digital cable (only 1 cable available):
CAble: [playback header (quality info)]
[sound chunk [Digital, L speaker]]
[sound chunk [Digital,Rear L speaker]]
....
1) You have to multiplex the signals together somehow,
2) You have to specify to the receiver the quality of the data being sent, so it knows how to decode the data
3) You need to tell it, how many channels are being sent, or if it sends 4 channels, and your decoder has only 2, it will play the rear and front mixed in a weird way (things wont sound right).
Its a transport problem. All dolby/dts does is define the transport. It should be relatively simple to implement our own.
We don't need fancy upscaling for computers generally (which is where fancy circuits come in).
But we do need a way to send multiple channels digitally to a receiver, with a single cable. Thats all that DTS and dolby digital does, but we cant use them
|
|
Auzy wrote on the 1 Apr 08 at 07:25
| |
Argggg.. Bastardry ubuntu brainstorm less then or greater then bug which will never be fixed it seems
|
|
Auzy wrote on the 11 Jun 08 at 02:10
|
Sorry, we cant use them because they are licensed, so you need to pay to use them.
By creating a new standard optical transport, we can support SPDIF without proprietry drivers, because as of yet, we cant freely implement dolby or DTS
|
Post your comment
|
|
|
