surround downmix clarification sought

[ux-3]

I've just read through faq and the links that a previous post today generated. I am still not sure if I figured it right and would be very greatfull for some clarifications or confirmation. I have a number of questions on this, so I'll _try_ to keep my text as organised as possible.

Case 1: When creating SVCDs which are very conservative on bitrate, I don't want to waste bandwidth on audio. I want to play it on a standalone, hooked to a classic stereo amp or a stereo TV. So far, I've used bitrate 96 or 128, joint stereo, downmix to just stereo, not surround. Is this appropriate for this specific purpose?

If I would leave it on joint stereo but select downmix to surround instead, would I actually be able to get surround sound on a simple surround receiver which has just two channel input (L/R) but surround speakers and Dolby Surround Logo? (ie my cheap Sony 315)
Some Sources say the Joint Stereo destroys the Surround Info, others say it works. What is true for DVD2SVCD when joint stereo is on?

Case 2: I am also trying to figure out, if it would make sense to upgrade my receiver to a 5.1 or spdif input model, on the premise that only SVCDs will be played. Assume I enconde with an audio bitrate of 192 or higher and choose Stereo chanels and surround downmix. Will this enable surround on a simple surround Receiver with just two channel input (like mine)? Will the digital Output (S/PDIF) from the standalone, if hooked to a digital surround receiver (yet to be bought) enable surround? My standalone also has 5.1 analog output, but my receiver lacks the corresponding input. Will the Standalone output 5.1 format from an SVCD or just two channels as I would expect.
Am I right that a 5.1 Analog Input Receiver is of no use for SVCD?

I apologize if I overlooked something, but I went through all the FAQs linked to in the previous post. Perhaps someone could help me with a (link to a) good article on this , or some direct info.
Thanks anyway!

ux-3

[DSPguru]

surround downmix usually is able to be reconstruced even when using j-stereo.

digital connection won't change the fact your signal is an uncompressed stereo track.

the surround downmix is an analog mix, and dpl (dolby pro-logic) decoder can restore the surround information anyhow.

Cheers,
Dg.

[ux-3]

Thanks for your reply!

So, if I understand you correctly, for the use of SVCD, any receiver beyond a two channel Dolby Surround would be a waste of money, since the only surround information I can get would be hidden in the analog stereo signal.

[ux-3]

Hallo again,
I "googled" through the groups on this topic again, and found a
lot of info for mp3. Since you are the author of Besweet, perhaps you can give me the missing info. I read that joint stereo encodes using different methods depending on signal and bitrate. This info was mainly about Lame, not 2Lame. What I read boils down to:
As long as the decoding "Joint Stereo" uses Stereo or Channel Difference (R+L R-L), the Prologic should still work. When it switches to Mono+Direction (Intensity Stereo), it kills the surround info. Different posters claimed that Lame (in joint stereo) would not encode in this detrimental mode when set to do CBR.
So whats the story with 2Lame or Besweet? If it is used in Joint stereo, will the Phase Info allways be kept?
What will happen when complex sounds come up? Would it possibly switch into Intensity Stereo mode?

I just came across a thread which claims that joint stereo will only do Intensity Stereo in 2Lame:
http://forum.doom9.org/showthread.php?s=&threadid=17580&highlight=joint+stereo

I get more and more confused. What is actually correct? I did search the Audio FAQ you pointed to, but most points are basic terminology or info. I couldn't figure it out.

[DSPguru]

Originally posted by ux-3
Thanks for your reply!

So, if I understand you correctly, for the use of SVCD, any receiver beyond a two channel Dolby Surround would be a waste of money, since the only surround information I can get would be hidden in the analog stereo signal. well, some people managed to burn an AC3 soundtrack on their svcd. in this case, you'll need a DD decoder.

as for channel coupling,
all stereo coupling modes are allowed for bitrates higher than 96kbps . and since dvd2svcd is only using CBR, we're on the safe side.

there's no joint-stereo in mp2, only intensity stereo, so i guess that dpl reconstruction will fail here.

[user]

I am a "produser" of music-SVCDs , too.

My experiences:

- good: having a good stereo hifi-equipment, obviously.
- Dolby Surround : better for movies, but not much better for music/concert-Movies,
a lot people prefer for music even stereo, not Dolby Surround.
- much better than Dolby Surround Pro Logic: Logic 7 = Dolby Pro Logic 2 = Circle Surround
this is good for music and for movies, too.
Logic7, DPL2, Circle are the names of the decoders of various companies.
DPL2 is the format how 5 channels are encoded into one stereo wave.
My impression is : that DPL or DPL2 stereo waves sound well, either played via normal stereo
(only front right and left speaker, stereo amplifier)
or played via Logic7, DPL2, Circle surround amp/receiver/decoder (my setup: 4 identical full 3-ways-
speaker, front left and right, rear left and right,
btw: at stereo times you did not need a center speaker, too, to
build up eg. the orchestra's middle sections... )
- 5.1 ac3 / dts : nice to have it.
But quality of sound varies dependent on your movie or concert-movie.

So if somebody is planning to go for surround sound, settling up at least 4 speakers and buying a
surround amp/receiver, then he/she should go for a Logic7/DPL2/ac3/dts capable amp/receiver.

Simple Dolby Pro Logic is out.
It is replaced by DPL2, for stereo-compatibility and for better surround.

But one thing remains still:

If you want to produce your self-made DivX/SVCD-concert-movie you will still
choose in most cases a stereo audio stream, not Ogg multichannel or ac3, because of bitrate or compatibility
problems.

And it would be really nice, if additional to azid.exe (which produces stereo or stereo-DPL
audio streams out of 5.1 ac3 eg.)
there would exist a kind of new azid2.exe, which is able to produce DPL2-stereo-audio-streams.
Or this DPL2 option is integrated into azid.exe.



Until Ogg becomes more and more popular or even better it becomes very well multichannel capabilities,
DPL2-stereo-audio-streams as (wav), mp3, mp2 and OGG !!!
would be a very well solution for true surround with low bitrates and very high compatibility
downwards to stereo and upwards for surround sound.

[DSPguru]

user, this it the dvd2svcd forum, we only discuss mp2 in here ;)

Dg.

[ux-3]

Hmmm....
thanks again for taking the time, but when I look at your first reply and then your second one, I am a bit irritated. In the first one you say that "j-stereo" will usually be reconstructed. In your second post, within a broader context, you say it won't work.

Also you say there is no "joint stereo" in mp2. Is the "joint stereo" selection in the audio tab (of either dvd2svcd or the besweetgui) just a misleading name and should be "directional stereo"?

I apologize for keeping up these questions but it really has not yet into place for me.

thanks
ux-3

[DSPguru]

just like user, i forgot i'm on the dvd2svcd forum, and i talked about j-stereo. but regarding mp2, we're talking about intensity coupling, and yes, the label should be changed in the gui :).

thanks for raising this up !
Dg.