Subject: Dolby Surround on MBone?

From: Kurt Kayser <[email-masked]>
Date: Thu, 24 Apr 1997 12:42:23 +0200 (MET DST)

Hi!

I was just wondering if somebody made already
experimented with transporting Dolby Surround Audio
encoded over the MBone?!

I'd like to get some bandwidth requirements
or some ideas to en-/decoding computing power
needed.

Greetings, Kurt Kayser
--
Kurt Kayser <http://www.ecrc.de/staff/kurt/> => Tel. +49 89 926 99148
ECRC European Computer Research Centre       => Fax. +49 89 926 99170
Arabellastr. 17, 81925 Munich, Germany       => E-Mail: [email-masked]

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From: Michel <[email-masked]>
Date: Thu, 24 Apr 1997 13:05:59 +0200

By experience I can tell that Dolby Surround information is still
fairly well decodable when encoded with mpeg audio at 112 kbit/s
("hifi" stereo)... You need at least a stereo channel to be able to 
dolby, so my guess is that the 112 kbit/s is very much the bottom limit
for mpeg layer transport.
One might argue that with less quality, you could achieve lower
datarates and still be able to decode dolby surround, but what's the
point of having crappy audio - all around you...?

Dunno if this helps though... maybe mpeg isn't the way to go here...

Michel. 

-- 
 Michel van der Laan	-	[email-masked]
				http://www.nijenrode.nl/~michel

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From: Hakan Lennestal <[email-masked]>
Date: Thu, 24 Apr 1997 13:04:18 +0200

> or some ideas to en-/decoding computing power

Should be quite possible for instance with ordinary MPEG coding as the 
back channel is encoded simply as a (delayed) difference between 
the left and right channel.
The "swplayer" from Xingtech uses MPEG and mbone (allthough not RTP).

Regards.

/Håkan

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From: Petri Helenius <[email-masked]>
Date: Thu, 24 Apr 1997 20:33:05 +0300 (EEST)

> Dunno if this helps though... maybe mpeg isn't the way to go here...
Quite the contrary, MPEG audio has been designed to preserve surround
information when a feature called "intensity stereo" is _NOT_ used in
the encoding process. As bitrates go, usually 112kbit/sec _WITH_ layer
three MPEG audio is the minimum for non-intensity stereo high quality
transport. I would recommend 128kbit/sec though.

However, I don't know what's the bitrate with layer 2 audio to achieve
surround decoding.

Pete

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From: "Peter H. Tebault" <[email-masked]>
Date: Thu, 24 Apr 1997 17:13:52 -0700

Kurt,

Check out this:
http://www.dolby.com/
http://www.dolby.com/tech/ac-3mult.html
for more detailed info.

I believe that the current incarnation of Dolby Surround [Digital],
using the AC-3 codec can transport full 6-channel (5 plus 1) audio at a
rate of about 320Kbps with six-channel.

I seem to recall reading that their AC-3 codec is flexible, and can
carry less channels of audio at less bandwidth requirements.  According
to the brief calculation on their page, 2 channels of cd-quality would
take 128*sqrt(2) Kbit/sec. of bandwidth, or 181.02 Kbit/sec.  Perhaps
they can use the same codec at a lower sample-rate, etc., to further
compress the audio.

Peace,
-Pete-

--
=============================================
Peter H. Tebault, Student - [email-masked]
fax 510 440 1770 ------ 1996 Neon Sport Coupe
=============================================