Audio: Whats Better (AC3) (Dolby Surround) or (AC3) (5.1)?

Discussion in 'Apple TV and Home Theater' started by imacericg, Apr 30, 2008.

  1. imacericg macrumors regular

    Jun 11, 2007
    In HB, several of my DVDs have selections for:
    (AC3) (Dolby Surround)
    (AC3) (5.1)

    One even has:
    (AC3) (Dolby Surround)
    (AC3) (4.1)

    Is the channel # (5.1/4.1) always better than "Dolby Surround"?
  2. killmoms macrumors 68040


    Jun 23, 2003
    Washington, DC
    Technically, I believe the term Dolby Surround is supposed to mean a stereo (2.0) audio feed that has surround information matrixed into it, which is separated by an amplifier processor: these are called Dolby Pro Logic and Pro Logic II.

    Dolby Digital on the other hand is supposed to refer to an AC3 audio track with 6 discrete channels (five full bandwidth and one LFE).
  3. err404 macrumors 68020

    Mar 4, 2007
    (AC3) (Dolby Surround) = 2 discreet channels
    (AC3) (4.1) = 5 discreet channels
    (AC3) (5.1) = 6 discreet channels
  4. Avatar74 macrumors 65816


    Feb 5, 2007
    According to the technical specifications for Dolby Digital AC-3, the difference is as follows:

    AC-3 Dolby Surround means that the file contains 2 discrete channels, L and R, into which a multichannel phase shifted Dolby Surround analog mix has been matrixed.

    Note that the correct terminology for this format is Dolby Digital 2.0 Surround, per Dolby Laboratories Licensing Corporation.

    Your receiver will decode the AC-3 digital bitstream and play back a stereo downmix if you are set up with only two speakers. If you have a full surround system, the receiver can decode the AC-3 digital bitstream and further demultiplex the analog-encoded Dolby Surround from those two channels into a full surround mix.

    When AC-3 5.1 or 4.1 is indicated, this is the case:

    AC-3 5.1, or "3/2.1" in its official designation, means that this is a Dolby Digital surround mix... not a Dolby Surround analog mix encapsulated in a Dolby Digital stereo mix.

    Note that the correct terminology for this format is Dolby Digital 5.1-channel Surround, according to Dolby Laboratories Licensing Corporation.

    AC-3 4.1, or "2/2.1" is the same thing... but this lacks a discrete center channel.

    NOTE that Dolby Digital is not automatically a surround format... it supports multiple channel arrangements including 1/0 (mono), 2/0 (stereo), 2/1 (L,R,Surround mono), 2/2 (L,R,SurL,SurR), 3/0 (L,C,R), 3/1 (L,C,R,Surround mono), and 3/2 (L,C,R,SurL,SurR).

    The technical specifications for trademark usage of Dolby Labs trademarks indicate that Dolby AC-3 Surround (also designated as Dolby Digital 2.0 Surround) specifically indicates that the AC-3 bitstream is stereo and contains a Dolby Surround analog matrix that can be decoded by Dolby Digital and Dolby ProLogic decoders.

    Dolby Digital 2.0 without the "Surround" in the naming indicates that the mix is simply stereo with no Dolby Surround analog matrix present.

    However, when the mix is Dolby Digital 5.1-channel Surround, it is a discrete six-channel bitstream WITH, in almost all cases of theatrical soundtracks, a Dolby Surround analog mix still matrixed into the front Left and Right channels for backward compatibility with Dolby ProLogic hardware.

Share This Page