[vorbis-dev] Re: Re: Re: How is 6 channels coupling made?

ChristianHJW christianhjw at users.sourceforge.net
Tue Sep 10 06:05:45 PDT 2002

"Moritz Grimm" <gtgbr at gmx.net> schrieb im Newsbeitrag
news:3D7DCD95.4DB1E19A at gmx.net...
> You're talking 1.0 RC3. With the 1.0 release the
> point-of-lossless-stereo-coupling went up to -q 6. Any huge bitrate
> jumps have been ironed out, so picking -q 5.99 (analogue to the popular
> -q 4.99 of RC3) doesn't result in significantly lower bitrates anymore.

Sorry !

I am reading 8 webboards and 28 Mailing lists, with more than 10 of them
being more or less closely related to Vorbis and simply didnt realize its q
6 now and that there is no jump anymore  :-) ! My bad ...

<p><"MiwongShaib" <miwongshaib at hotmail.com> schrieb im Newsbeitrag
<How much does the coupling gain? From my encodings with OggDS seems
<A 6 channel encoding is 2.3 times larger filesize than 2 channels encoding
<the same quality.
<Of course the additional channels (expecially the subwoofer) have less
<than FL and FR, but it seems to me that coupling doesn't gain much.
<Or maybe Tobias has disabled any coupling, even in 2ch, in order to be
<to the number of channels entered?

I dont think Tobias has changed anything in the encoder concerning coupling,
but as you estimate its more likely that Vorbis encoder spends only very
small bitrate on LFE channel for example, due to the nature of the signal.
Same or similar should be valid for the center channel ( mostly voice ) and
surround channels.

After having thought about the sense of a coupling for a typical movie 5.1
track ( not music, like live recordings ) , it seems to me the main purpose
of a channel coupling is at least questionary, as there may be not much
common signal.

While talking to Monty on this subject i suggested that maybe a selectable q
level for the 'unimportant' channels, like LFE/center/rear channels would be
sufficient in 1st instance to bring filesize down significantly, but it
seems thats not feasible with current Vorbis encoder layout.

>"Tim Ivorson" <tim.ivorson at mailandnews.com> schrieb im Newsbeitrag
news:3D7DC60E at mailandnews.com...
> Where the input sound is ac3, is using 6-channel vorbis really preferable
> using high quality mono vorbis or not converting the sound at all (given
> oposition in the ogg community to reencoding)?

Thats depending on the your personal use have in mind. If you want to
preserve max. quality, buy the DVD a 2nd time. If you want a backup of the
movie in very good quality, go for a 2 CD rip and keep original AC3. If the
movie is not important enough to keep 2 CDs for it, why not make a nice 1 CD
rip with a 5.1 Vorbis at bitrates 150 - 200 kbps ( thats the aim ) in decent
quality ?

> Does ac3 use lossy channel coupling?

No idea. Think so.

> I imagine that the bass channel is encoded differently to the others. How
> it encoded?

Midas, the developer of acid ( AC3 decoder ) is an expert in AC3, he might
be able to tell ...


<p><p><p>--- >8 ----
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