[vorbis] Multichannel files

[David Balazic]

Wilson (defiler at null.net) wrote :

Please CC replies to my private email ( click REPLY-ALL or something like that )

> ----- Original Message ----- 
> From: "David Balazic" <david.balazic at uni-mb.si> 
> To: <defiler at null.net>; <vorbis at xiph.org> 
> Sent: Thursday, November 15, 2001 8:45 AM 
> Subject: ATTENTION Re: [vorbis] Multichannel files 
> 
> > I noticed that my previous message is not very complete so I send here an 
> "enhanced 
> > version". Please disregard the old one an reply to this one only. ( you 
> can delete 
> > the ATTENTION word from subject ) 
> > 
> > Wilson (defiler at null.net) wrote : 
> > 
> > > There are two ways to decode multi-channel audio. In hardware, or in 
> > > software. 
> > > Hardware: A receiver or processor takes a Dolby Digital (for example) 
> stream 
> > > and converts it into something your amps/speakers are interested in. 
> > > Software: Your PC decodes a 5.1 audio stream into six discrete audio 
> streams 
> > > and passes them to analog output. 
> > > 
> > > Sound cards that can handle what is described in the second case are 
> fairly 
> > > rare. The Hercules Game Theatre XP, the M-Audio Delta Theatre ($$$), 
> etc. 
> > 
> > I have a 4 year old 4 channel sound card ( Ensoniq AudioPCI , 20 USD ). 
> > Almost all newer cards support 5.1 output, like the SB Live! 5.1 series. 
> > That is 6 analog outputs. 
> > A Live! Player 5.1 is 40 USD here at my place. 
> > 
> Actually, the Audigy (replaces the Live!) lets you do EITHER discrete 
> subwoofer OR discrete center in analog mode. 
> http://www.3dsoundsurge.com/reviews/AudigyEI/Audigy-p2.html 

A quote from the page :
"The Digital out/Center-subwoofer can, just like the Live 5.1 card,
be used for either digital output or when in analog mode as the
center/subwoofer output."

This page says that it is either :
- digital out put
- a combined analog center/subwoofer output. It is a stereo connector.
  One channel is the Center and the other is the subwoofer.

> In other words, it doesn't do what we need. All the SB cards are geared 

Yes it does.

> toward 5.1 output via S/PDIF / Whatever to a receiver/decoder. 

Wrong, obviously.
 
> > > Most people don't have them. Doing real 5.1 output from the PC without a 
> > > receiver that locks you into Dolby Digital is either expensive (full 
> pre/pro 
> > > combo) 
> > 
> > There was a surround amplifier available for 1000 ATS in Austria recently. 
> > That is cca. 64 USD. It has 4(6) analog inputs and can drive four speakers 
> > ( it has 4 amplifiers ). You need another normal 2 channel amplifier to 
> get 
> > an 5.1 setup. I believe it also has a Dolby ProLogic decoder, but that is 
> not 
> > of interest to us. Is has about 50 Watts power per speaker. 
> 
> I meant expensive for quality equal to a cheap 5.1 receiver. I don't mean to 
> insult a $64 amp, so I won't say anything about it. :)  

See below "about expensive"

> > 
> > Or you could use 3 normal stereo amplifiers. I also believe most newer 
> "movie" 
> > or AV amplifiers have 6 channel analog input too. 
> 
> Yes, many do have 6 analog channels.. Again, the trick is getting 6-channel 
> analog output from your PC. 
> Also, these things are expensive. 

See below "about expensive"

> 
> > 
> > > or rare (analog 5.1 multimedia speakers with LFE management. Hard to 
> > > come by.) 
> > 
> > Creative/Cambridge SoundWorks DeskTop TheaterT 5.1 DTT2200 : 128 euro ~= 
> 112 USD 
> > It about 156USD in Slovenia. 
> > 
> 
> The DTT2200 does not offer 6 discrete channels. Yes, it accepts analog 

Yes, it does.

> inputs, but not 6 of them. Thus, you don't have a true center channel or LFE. 

Yes, it does. Yes, you have.

> Here's a (crappy) photo of the connector panel I found on the net. See? The 
> DTT2200 appears to generate a matrixed center channel from the left and 
> right channels. 
> http://www.tech-gods.com/reviews/227/busysub.jpg 

On page 11 ( eleven ) of the DT2200 manual ( available at 
ftp://ftp.europe.creative.com/pub/online_library/speakers/DTT2200_Users_Guide/English.pdf )
it is clear that it has 6 analog inputs.

> 
> > It can be bought in any computer shop. 
> > 
> > > To play a multi-channel Ogg file through a receiver, the receiver would 
> have 
> > > to directly support Ogg, and the sound card drivers would have to 
> support 
> > > pushing the Ogg through Toslink or S/PDIF. An alternative is to 
> transcode 
> > > the Ogg output on the fly into AC-3 for transport, but then we're not 
> > > patent-free anymore. 
> > 
> > Just decode to 6 independent channels and send them thru the analog 
> outputs 
> > of the 5.1 sound card. 
> > 
> > Now if someone wrote a program that uses 4 four channels of my AudioPCI 
> and 
> > the 2 of the on-board sound to get 5.1 , that would be cool :-) 
> > 
> 
> Yes, that would be cool. Just get two "4 speaker" sound cards, and you'd 
> support all 6 speakers. Not exactly a mainstream concept, though. 

As volsung said , synchronization is a problem. Maybe checking the position
( most card support sample accurate position report of the current played sample,
AFAIK ) and dropping samples on the faster DAC ?
It is probably a difficult to solve problem, because everyone is avoiding it
like the plague :-)

About expensive :

What are you complaining about ? What is expensive , compared to what ?
A DT2200 speaker + a Live! Player 5.1 is about 180 USD. That is very cheap
for a 5.1 system if you ask me. It is maybe not hi-fi , but a single hi-fi
speaker costs that much and you need 6 of them ! And an amplifier ( 100 USD
minimum ).


-- 
David Balazic
--------------
"Be excellent to each other." - Bill S. Preston, Esq., & "Ted" Theodore Logan
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