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MP3...in Surround Sound
A number of people sent in the latest news from the fine folks at Frauhofer that they are expecting to have surround sound working for MP3s by July. The details are pretty sketchy in the article, but supposedly it won't be much more space per MP3s, and existing players will work with it.
You couldn't convert your mp3's to surround because the source is stereo... if you want surround just run it through PL2 for pretty good on the spot surround sound.
Ogg Vorbis have had support for this for some while.
What I'm not sure of is if the support for "joint" surround is there. (Like joint stereo, only for surround)
Who wants to use a proprietary sound format, when they can use a much more appealing open format.
Vorbis is also intended for lower and higher sample rates (from 8kHz telephony to 192kHz digital masters) and a range of channel representations (monaural, polyphonic, stereo, quadraphonic, 5.1, ambisonic, or up to 255 discrete channels)
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http://xiph.org/ogg/vorbis/doc/vorbis-spec-intro.
MP3 is and was always proprietary...
Here's the deal.
By far, the most popular algorithm in use for surround sound encoding is Dolby's AC3 (I can say this, because it's on pretty much every DVD, and nothing comes close to its penetration even in the audio space -- not even DVD-Audio). AC3 itself is a pretty fascinating codec; one of the more interesting things about it is that each additional channel requires less and less bandwidth to tack on. This is because there tends to be massive correlation between channels -- either the same sound is coming from multiple directions, or a sound is coming from one direction and all the others are silent, or some combination therein. AC3 encodes this quite efficiently, and thus gets really high quality surround sound in surprisingly few bits.
I suspect they're engineering a similar mode for MP3 -- hopefully something a little nicer than Joint Stereo, which basically works by doing a mono mix and specifying which frequencies are louder in which channel. No, this doesn't work very well. Concievably, we could see something like VBR on a per-channel basis, but I suspect this would cause existing decoders to collapse. I do believe it's possible to place extra data between MP3 granules; I suppose they'll get their backwards compatible surround mode worked into there.
--Dan
Yep -- there is SACD, which is kind of like DVD audio with the 5.1 encoding, but if you put a hybrid SACD disc in a regular CD player, you get the front stereo pair. It's been around for a while but isn't incredibly hot right now. Sometimes you can find SACD discs at Best Buy and such.
The system you mention is "Dolby Stereo". But "sum" and "diff" aren't the correct terms. Any signal that is in 100% phase on both left and right will end up in the center channel. Signals that are out of phase end up in the rear.
Now "Dolby Stereo" sounds like it is, well, stereo. So the marketing department decided at some point that it should be called "Dolby Surround", which is fair enough. "Pro Logic" is "Dolby Surround" for use in home A/V amps, but with "Pro" electronics (logic). Another marketing term for the same thing.
That system should work fine on any MP3. Stereo MPEG audio on DVDs (so not the Dolby Digital or DTS tracks) quite often have Dolby Stereo/Surround encoding on them as well.
The truth is that the BBC article doesn't have enough information and I think "Surround" is used as a general term to indicate more than two channels of audio. So no way of knowing what they actualy mean.
From the article, again:
There's no extra channels, just an extra layer telling the player how to manipulate the two existing audio channels to obtain a surround-like effect. While the merits of this approach alone make me skeptical, what really bothers me about this is how different players are all going to have completely different implementations of using this extra layer of data to manipulate the audio channels, meaning we're going to have no consistency whatsoever with how it even sounds.