Are there any free ones?

Free and opensource AC-3 encoder is Aften.
Btw: what is Dolby LPCM?

To my knowledge, there is no such animal.

I actually meant this
http://www.dolby.com/consumer/technology/mlp_lossless.html

What's better for compressing 5.1 wav? MP3 or AC3?

MP3 doesn't support more than stereo.
Though, there is so-called "MP3 surround" without wide support in hardware and software. The de-facto "better" (more support and adoption) surround format is DolbyDigital.

EDIT. The details are at http://www.mp3surround.com

Just to nick-pick, actually there is a multichannel MPEG format, but I think it's MPEG2 Layer 2, and probably not much compatible with MP3, and it's support is limited to a very few Pioneer recievers

Is "dolbydigital" AC3?

http://en.wikipedia.org/wiki/Dolby_Digital

I see. There is no MLP lossless encoder or anything that can encode into lossless formats?

Is AC-3 the best codec for lossy 5.1 compression?

For MLP/DVD-Audio, Sonic DVD-Audio Creator includes the MLP encoder. List price is $20,000 US. Minnetonka Audio Software sells their discWelder Chrome II with MLP encoding support for $2,995 US. You can also snag the encoder directly from Meridian for $2,500 US. I assume it's just a CLI encoder, but I'm not actually sure.

No, you're confusing with "MP3pro". "MP3 surround" is fully backwards compatible with plain MP3 decoders (but no 5.1 surround sound in that case). "MP3 surround" is MPEG1 Layer 3 with sort of extension.

EDIT. The details are at http://www.mp3surround.com

Hopefully there will be a free MLP encoder by the end of the Summer. Ramiro Polla is currently working on one for FFmpeg as part of the Google Summer of Code.

You just confirmed that both are in fact very similar. One adds fake high frequencies, and the other – fake surround. Both contain regular MP3 frames that can be played everywhere.

What happened to Aud-X? It promised to do the same thing as "mp3 surround".

Cool!

Well, no, he didn't confused that, just was refering back to the times of DVD market introduction, when there was MPEG2 Layer 2 Multichannel defined as the standard for European (that is region 2) DVDs. Only for a short time though, and was dropped in favour of Dolby Digital. Still have 2 or 3 of these disks. Pioneer, Sony and of course Philips had some receivers supporting it.
And being Layer 2 it is not compatible with Layer 3, although a full MPEG1 Layer 3 decoder should be able to decode the L2 base stream....so much for history.

There is a ISO specification for Layer III multichannel, but it has never been really used by encoders.
The so called "mp3 surround" is a different, non standard thing.

The statement ist true, but the reason is not. As you say, the layers differ entirely, preventing them to interoperate in any way. There is no such such thing as a "base layer", and layer III is *no* extension bitstream to layer II.

Actually, the reason is because the standard requires it:

ISO/IEC 11172-3:
"An ISO MPEG Audio Layer N decoder is able to decode bitstream data which has been encoded in Layer N and all layers below N."

The word "layer" doesn't have the usual meaning here, maybe the three different codec algorithms (which have been developed more or less independently at different labs) have been named like that because they share common functional building blocks, and each layer adds some more; however, this does not mean the bitstream is layered.

Layered bitstreams exist in form of the extension layer of MPEG-2 Multichannel, DTS 96/24, MPEG Surround extensions, hybrid lossless coders such as SLS, and in MPEG-4 BSAC (optimized for bitrate scalability).


W.

Actually, it is standardized under the name "MPEG Surround" in ISO/IEC 23003-1:2007. It is very generic and can be applied to any codec and any number of channels reductions, such as 5.1>2.0, 5.1>1.0 or 7.1>4.0, and delivers a multichannel impression at a quality level somewhere between real discrete systems and matrix systems.

Layer III is of course supported and marketed under MP3 Surround, too; AFAIK the MPEG Surround algorithms were first developed for MP3 Surround and only later generalized to arbitrary codecs.

W.


Also see http://www.chiariglione.org/MPEG/technolog...d-mps/index.htm