6 channel discrete vs dolby digital II?

Discussion in 'Apple TV and Home Theater' started by Keebler, Mar 25, 2009.

  1. Keebler macrumors 68030

    Jun 20, 2005
    Hi folks,

    Just wondering what the difference is b/n the 2 (aside from the 6 channel maybe having a larger file size)?

    I have a 5.1 DD setup. So far, DD has worked for me, but just wondering if 6 channel is better?

  2. jimothyGator macrumors regular


    Jun 12, 2008
    Atlanta, GA
    Dolby Digital does have (up to) six discrete channels. Perhaps you're thinking of Dolby Prologic, which is "matrixed" to multiple channels but only encoded as two discrete channels. In other words, the receiver takes a stereo signal and processes it to give surround sound.

    Dolby Digital is one of a few ways of encoding multichannel audio. DTS is a competing encoding. Most encodings are compressed, though DTS-HD Master Audio, found on many Blu Ray movies, is uncompressed. I'm not sure if Dolby has an uncompressed, multichannel encoding available.

    EDIT: Dolby TrueHD is uncompressed, an apparent competitor to DTS-HD Master Audio.
  3. dynaflash macrumors 68020

    Mar 27, 2003
    um, not sure what you are talking about. HB's aac mixdowns ?
  4. almostinsane macrumors regular

    Feb 9, 2008
    TrueHD and DTS MA use lossless compression. PCM is uncompressed.
  5. HiFiGuy528 macrumors 68000

    Jul 24, 2008
    from my understanding of what I've read, 6.1 discrete is passing 6.1 channels of signals to be processed by a device with 6.1 decoder. This means you have to connect your Mac to a 3rd party device to run 7 RCA cables to your surround reciever.

    From Handbrake:
    "Another method is to create 5.1 channel AAC audio tracks. For the Track Mix, select "6 channel discrete" from the drop-down menu, and your movie will contain discrete surround sound in the modern AAC format. This takes up less space than AC3: instead of 448kbps, you can do well with 384kbps (64 kbps per channel). Its real benefit is that it doesn't make QuickTime barf. Sadly, it is very difficult to hear all those discrete channels of sound. It cannot be sent over an optical cable to a home theater amp. If you try, whether on a Mac or an AppleTV, you will only hear "downmixed" surround sound, similar to Dolby Pro Logic. To hear the discrete surround sound in all its glory, you will need to attach an analog surround sound device to your Mac. One popular device is the Griffin FireWave. Then, you have to attach a cable to your amp/receiver for each of the six speaker channels. It cannot be done over optical/HDMI".


    Technical Specifications
    Audio Ports: 3 - 1/8" (3.5mm) stereo minijacks (Left/Right, Center/Subwoofer, Left Surround/Right Surround)
    FireWire Ports: 2
    Supported Audio Formats: Dolby Digital, Dolby Pro Logic II
    Additional audio configurations are supported through Mac OS X's Audio MIDI Setup utility
    Frequency Response: 20-20,000Hz
    Line-out voltage: 2Vpp
    Size: 132mm (5.20”) wide x 77mm (2.83”) deep x 25mm (0.98”) tall
  6. vhase macrumors newbie

    May 12, 2009
    A different approach

    Call me nuts - but here's my current "logic" on this (sorry...) :rolleyes:

    Currently, the Handbrake Pro Logic II setting does not encode the .1 (sub) channel. This really bummed me out, because I didn't do my homework, and encoded most of my DVD's before actually being able to hook up to a new surround AV receiver. So, when I noticed things were sounding flat, and specific examples of heavy rumble that I knew by heart that were simply not there - I had to re-group.

    PROBLEM 1: No sub woofer for Handbrake's Pro Logic II - bummer.
    PROBLEM 2: 6 Channel Discreet setting preserves the individual channels, but is converted to a stereo signal through the TOSlink cable. Bummer.

    My receiver's Pro Logic II setting converts that stereo stream back into surround. No, it's not digital to be sure, but the matrix INCLUDES the Bass frequencies that handbrakes PLII converter leaves on the cutting room floor.

    Since I started re-ripping my collection with the 6 channel discreet setting - all the new rips have a heckuva lot more oomph. And I don't think it's only because the discreet setting defaults to 384k for the channels, as opposed to the PLII maxing at 160k - I really think there is much more bass brought to the viewing party by using this 'round about method.

    As I said - call me nuts, but that's the direction I'm taking. Not perfect, but much more satisfying than the PLII setting. It does add another 10% or so to the files with the higher audio bandwidth, but hey, that's why we've bought those nifty terabyte drives, right? :)
  7. eddyg macrumors 6502

    Sep 5, 2003
    Christchurch, New Zealand
    ANy particular reason you don't simply pass through the original untouched AC3 Dolby Digital from the DVD and let the Apple TV or Mac pump that out of the optical to your AV receiver?

    Then you will have the exact same audio as when playing from the DVD.

    Personally I think it would be crazy to extract the 5.1 channels from the AC3 and reencode as AAC just to save a few bytes of file size. That's just asking for a world of hurt. There is no way that's going to sound better than the original AC3.

    Mind you - one benefit of multi-channel AAC is that you can transcode from DTS to AAC and get better audio than the AC3 that way (since MP4 doesn't yet have DTS pass-through).

    Cheers, Ed.
  8. vhase macrumors newbie

    May 12, 2009
    I would love to use pass through. Unfortunately, it doesn't work properly. Even with Perian, you wind up with the center track all over the left channel, and a funky, compressed sound field. Not fun.

    According to Handbrake, it's a Mac flaw:

    "The next method is called AC3 pass-through. This just copies, bit-for-bit, the Dolby Digital soundtrack on your DVD. AC3 pass-through is possible in the .avi, .mkv, and .mp4 containers. QuickTime cannot understand AC3 audio. You can download a 3rd party QuickTime component from the open-source Perian project, which will allow the files to play in QuickTime, although pass-through from there to a surround receiver is currently broken due to a bug on Apple's part. If you use the .mp4 container, you can only play the audio in VLC, Perian, or on the AppleTV, and you have to end the file name in .m4v instead of .mp4. Using AC3 in .mp4 this way is standards-based, but it's a new standard and not everyone is on board yet. To use pass-through, make sure you have AC3 audio selected in the Codecs pop-up menu."

    All-in-all, a dampening of my spirits...

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