Stereo playback with 5.1 audio

dth wrote on 12/30/2003, 2:05 PM
I'm working on a DVD project that will include 5.1 audio. My question is how this disc needs to be authored to be compatible with stereo playback. Commercial DVDs have multiple audio tracks - stereo, DD 5.1, DTS 5.1, etc. but DVDA only offers one audio track per video stream.

In the case of a DVD with only 5.1 audio, what comes out of the L/R jacks during playback? Does the DVD player mix the rest of the channels or is it just the L/R components of the 5.1 signal? My main concern is the center channel which could end up missing during stereo playback if it's not mixed into L&R.

PLEASE don't tell me it's player-dependent! :-)

Thanks.
- Dave

Comments

RBartlett wrote on 12/30/2003, 3:25 PM
It is in the spec and chip designs for a fixed mixdown of 5.1 to 2.0 to occur on the analogue outputs of a DVD player or PC line-out. The sockets that can service 5.1 (local decoder or outboard digital decoder) will do their best unless overridden if the player can.

Better still, the spec also attempts to load the stereo image with the analogue expansion of dolby-prologic to represent the surround channels. Not 5.1, but still compatible.

Machines that can only play stereo PCM, or DolbyDigital 2.0 or even either PCM or MPEG-1-Layer2 2.0 tracks are somewhat like the proverbial hens teeth.

A bit like any enhancement, it doesn't go amiss to advise the client on how to best setup his system to ensure the best reproduction. A good quote is to refer troubled viewers to the list of manufacturers that are part of the DVD-Forum and to identify the month/year of their joining compared to the origins of their player.

I'm not exactly sure of what happens to the stereo channels if the "TV" doesn't have prologic (Dolby Surround analogue) support. The mix method is probably described adequately on the dolby site. Not that this excuses this from being a good future addition to the Sony user manuals.

I'd be surprised if "zilch" of the surround/sub channels appeared on L/R as baseband audio. Definitely be assured that your worries have been catered for but be completely content with your wares before you go to a DVDR transfer to a replicated disc.
jkb242 wrote on 1/1/2004, 8:57 AM
Are you tryinbg to cover both 5.1 and stereo equipped players? I think if you author the DVD in DVD_A using the custom rendering menu for dolby suround 5.1 for the audio track, the DVD should pocess a stereo (2 channel) output when the DVD is played on a stereo only player. I have not tried this but I know for a fact that DVD's autthored with audio rendereing using the provided template in DVD A plays from both channels of a 2 channel system.

I cannot tell you if the sound is truely stereo. You do realize that you must render the audio tracks separately from the Video?

Please post your results for interest to all.
dth wrote on 1/4/2004, 12:34 PM
I've actually rendered the 5.1 AC3 file in Vegas. Playing back the authored DVD (on a player with an optical 5.1 output but only L&R analog outputs), I can confirm that I get a stereo downmix out of the DVD player's L&R audio outputs. On a DVD player with analog 5.1 outputs it required some configuration but I was eventually able to get the same result.
- Dave
David_Govett wrote on 1/5/2004, 1:07 PM
It mixes fine but I'm getting a definite phazey sound when the surrounds play back by themselves on a non surround system. I'm working on the QLSO demo & marketing DVD and we solo the surround samples to the rear channels to show what they sound like and they sound very strange and out of phase in stereo playback. It sounds like the system is trying to at least imitate surround sound and sort of acknowledge the existence of surround material or something. Perhaps its the pro logic imitation.
Once it is all mixed and playing together with the front channels, it seems to sound pretty normal.
I know that I experience this on some TV shows on my home TV which is just stereo. Every now and then, the dialog or a some effects wind up in the middle of the room or behind or several feet outside the speaker range. Its cool sounding but definitely not intentional.

Any ideas on this?
David Govett
farss wrote on 1/5/2004, 3:12 PM
I've had this happen by intention, our TV has a go at creating surround from stereo. Mostly it does nothing until you're lying there in a daze late at night and suddenly something leaps out from somewhere behind you!

Also I've had some wierd things happen with the Dolby decoders in cinemas. If the inputs are configured as surround even though they're only two channel it'll try to create a surround mix using prologic. Wild effect, sound whizzing around the cinema. Definately not natural