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RE: DVD audio down mix, original stereo?

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Neil Wilkes

In Reply to: RE: DVD audio down mix, original stereo? posted by kayaker on June 22, 2007 at 07:27:49

No, Downmixes are most definitely NOT created by the players.
Downmixes are created at the MLP Encoding phase, and verified there.
There are no players that automatically downmix 5.1 to stereo in DVD-A - if you play a 5.1 only title in a stereo player, if there is no downmix you will get L & R only. NOT a downmix.

FWIW, it is actually very bad practise to create a 5.1 only title - Sonic throws a warning telling you the title cannot be presented in stereo.
To check if a title is genuine stereo or a downmix, simply press the AUDIO button on the remote. PGC Block authoring is very common for 5.1/stereo compatibility, and is done by creating group 1 as 5.1, then adding a second stereo stream to the same group. Playback can be set to access Group 1 on disc load, and playback will access the stream that best suits your player configuration. A 5.1 player will access the 5.1 stream, and if there is no dedicated access to the stereo PGC the AUDIO button, as in DVD-Video, can always switch the stream.

Follow Ups:

Hmm, Have you verified this? - Ted Smith 11:17:56 09/12/07 (3)
Howdy
I took a test disk with channel identification tracks and played it on my Denon 3930. Guess what? When HDMI was selected to be the pure output, the left front and left rear channels both came out of the analog output to the front left speaker (and not the rear), and similarly for the right channels. This seems pretty unambiguous and in direct contradiction to your statement that "Downmixes are most definitely NOT created by the players."
-Ted

Edits: 09/12/07
- RE: Hmm, Have you verified this? - Neil Wilkes 11:29:20 09/12/07 (2)
  Ted.
  
  To quote directly from the Sonic Manual (AKA MEI DVD-Audio Creator)
  
  SMART CONTENT AND DOWNMIXING
  DVD-Audio allows � but does not require � both stereo and multichannel
  mixes of the same music to be delivered on one disc. To ensure that a DVDAudio disc will always play back, even when the only available mix is
  multichannel but the playback system is two-channel, players must support
  the SMART Content system.
  SMART allows producers to determine in advance a set of downmix
  parameters ("coefficients") defining the relative level, panning and phase
  that will be applied to each channel of a multichannel mix if it is combined into stereo. A SMART "downmix" will only be played if a discrete 2-channel mix of a given program has not been included on the disc.
  SMART downmix coefficients may be prepared in OneClick DVD (if the
  target audio format is MLP) or in DVD-Audio Creator�s Import Audio
  application (see Chapter 4, section 4.2.6).
  
  Summed up - if there are no co-efficients encoded into the PPCM or MLP stream, the player will only output Left & Right.
  If you are hearing Ls/L and Rs/R at the same time, then the stream includes a downmix coefficient created at authoring.
  A straight 5.1 stream cannot be automatically downmixed by the player.
  The co-efficients are added in one of 2 places:
  1 - By the MLP Lossless encoder, or
  2 - By the Sonic IMPORT AUDIO applet that forms a part of the MEI Authoring suite when using RAW/PCM or AIF files instead of MLP.
  The players cannot do this, as there are too many variables, and the likelihood of clipping or distortion - especially with modern uber-compressed material - precludes the use of any automatic systems, as correct distortion free playback cannot be guaranteed unless the downmix is verified.
  - I misunderstood your point - Ted Smith 12:38:05 09/12/07 (1)
    Howdy
    
    Now I see what you were saying, I misunderstood. I thought you were saying that no player would downmix a 5.1 disc (which didn't have a stereo section) for stereo only output. I now see that you were saying that the recipe for any such downmixing is set on the disk, and not presumed by any given player.
    
    -Ted
    - RE: I misunderstood your point - Neil Wilkes 13:08:06 09/12/07 (0)
      Ted.
      
      If anyone needs to apologise it is me - I am seriously poor at expressing what is in my head a lot of the time - fingers cannot type fast enough to keep up with the flow!!!
      (Hey - I am a sound engineer from the Live industry after all!)
      
      But you are essentially correct - the stereo playback is set on the disc, not in the players.

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