why do Dolby Digital sountracks sound so GOOD?

Discussion in 'AV Receivers' started by eddieZEN, Mar 26, 2005.

  1. eddieZEN

    eddieZEN Second Unit

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    Lately I've been noticing that whenever I watch movies that have strong soundtracks, especially jazz and classical but normal rock/pop too, that my speakers (Ascend 340s) really SING! Am I imagining things, or do movie soundtracks sound much richer than Dolby II Music or Neo:6 Music or Stereo or Pure Direct for some reason?

    My DVD player is a very basic Panasonic with a digital coax connection, generic (lowest end Recoton) cables; my CD player is a Sony ES carousel on a generic optical cable connection. Receiver is a Marantz 5400.

    So it can't be to any huge difference in connections or components...is it just something about the the Dolby Digital format? How does this compare to SACD or DVD-A music quality? All my CDs are the old fashioned 2-channel variety.
     
  2. amatala

    amatala Stunt Coordinator

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    Dolby Digital encoded sound tracks (either Stereo 2.0 or Multichannel 5.1) are always encoded in 48KHz/24bits (for each channel).
    CDs are encoded in PCM 44.1KHz/16bits so this means the Dolby-encoded DVD soundtracks bear much more information than plain CDs. Please note that multichannel Dolby Digital soundtracks do not take up more space than their stereo PCM counterparts because DD uses lossy compression while PCM does not.
    The Dolby PLII and DTS Neo:6 you have mentioned are not encoding formats, but algorithms that can create additional channels by extracting information from plain Stereo (or matrix-encoded Stereo) soundtracks. Playing your CDs in PLII or Neo:6 will not add addidional information to the source, it will only simulate surround sound.
    So DD tracks should sound better than CDs, but they don't sound nearly as good as DVD-A soundtracks which normally use 96KHz/24bits or even 192KHz/24bits LPCM encoded sountracks.

    Hope this helps.
     
  3. eddieZEN

    eddieZEN Second Unit

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    Amatala,

    Thanks, that's the best explanation I've heard and I've posted this question on 3 different audio boards!

    Sigh, looks like I may be starting yet another expensive habit then: DVD-As!

    BTW, are DVD-A and SACD about the same quality?
     
  4. Kevin C Brown

    Kevin C Brown Producer

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    No way. Because Dolby Digital soundtracks use lossy compression they definitely do NOT sound as good as a CD.

    The ratio of sound information per channel is much lower for DD than for CD.

    Do the math: 6 channels of info in the space for 2 channels.

    And, it's actually even worse than that. I believe that the bit rate for most DD soundtracks is 448 kbits/sec. That is for all 5.1 channels. The bit rate for a CD is 1411 kbits/sec for 2 channels. CD is much better quality than a Dolby Digital soundtrack.

    The reason why Dolby Digital soundtracks sound better than DPL II or DTS Neo:6 is that a DD soundtrack delivers *discrete* info to all 5.1 channels in your system. Both DPL II and DTS Neo:6 use matrix technology to *generate* 5.1 channels of info from the original 2 channels of the source.

    It's the discreteness of that multichannel presentation that you are enjoying.
     
  5. eddieZEN

    eddieZEN Second Unit

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    > The reason why Dolby Digital soundtracks sound better than DPL II or DTS Neo:6 is that a DD soundtrack delivers *discrete* info to all 5.1 channels in your system. Both DPL II and DTS Neo:6 use matrix technology to *generate* 5.1 channels of info from the original 2 channels of the source.

    This is a persuasive point, were it not for the fact that I find the DD soundtrack actually sounds better than CD *STEREO* and CD *SOURCE DIRECT*...and THAT's what blows my mind!

    Of course, it's possible that most of my CDs may just be crappy recordings...
     
  6. Kevin C Brown

    Kevin C Brown Producer

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    Eddie- Even a mediocre 5.1 presentation will *sound* better to most people than even an upscale 2 channel any kind of recording. Psychoacoustical thing. Human beings are 3-dimensional creatures. 2 ch stereo CD, lp, MP3, whatever, just can't cut it for a 3-D sound field. Lots of studies have been published on this btw. [​IMG]

    Here's an experiment: take whatever DVD and CD you want to compare. Down mix the Dolby Digital recording to 2 channels. Then compare to the CD. You also have to make sure that the levels are balanced in terms of what you are hearing (most people listen to movie soundtracks louder than CDs, so that plays a role too). If you listen close for imaging, depth, space, etc, and if your system has high enough resolving power, and yes, if it's not a poorly mastered CD, the CD should sound better. Listen in particular to the quality of the high frequencies. Extension, definition, channel separation between left and right, etc. This is where CD will easily dominate.
     
  7. amatala

    amatala Stunt Coordinator

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    Kevin,

    You cannot compare the birates of two completely different formats (especially when one is compressed and the other not).
    Please do not forget that DTS is also a format that uses lossy compression (a little bit less aggressive than DD) and yet a DTS 48K/24bit soundtrack is virtually identical to the same 48/24 PCM encoded soundtrack. DTS also has a lower bitrate than PCM 44.1/16 and yet it is immensely superior.
    A stereo DD track in 48/24 will sound better than its CD counterpart even if only 2 channels are being used.
    The difference in quality between formats cannot be measured in bit rates, it should be measured in word lengths (the 24-bit word length offers huge improvement over the 16-bit word length) and sampling frequency (48K does not offer a huge improvement over 44.1K, but 96K definetly does). After all, the goal of all these formats is to produce an analog sound as pure and natural as possible after decoding, so increased word lengths and sampling frequencies matter most. Ideally the use of compression should have no impact on the final result - maybe this is not completely true about the DD compression, but is definetly is when it comes to DTS compression.
    We should not forget that, with the exception of real low quality formats (like MP3), CD offers the lowest sound quality available on digital media today (after all CD technology is 25 years old)...
     
  8. eddieZEN

    eddieZEN Second Unit

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    Kevin,

    Well the thing is I mostly listen to 3.1 when watching movies because I'm too lazy to hook up the surround speakers (wife doesn't want to trip over wires so I plug and unplug bananas each time I want the rear channels---since I mainly watch dramas I don't often want the extra 2 channels) so I don't think it's a question of 3D versus 2D.
     
  9. Scott Lawrence

    Scott Lawrence Stunt Coordinator

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    You may want to double-check that. I think you're right on CD as it is 150 kiloBYTES per sec, so 1411 kbits/sec sounds about right. However, I think you have the wrong unit of measurement for DD 5.1. I'm pretty sure it's 448 kiloBYTES/sec not 448 kiloBITS/sec.

    In fact, question 33 in the Dolby Digital FAQ on Dolby's site provides the answer, it IS 448 kB/sec not kb/sec, or about 3 times that of CD bitrate. When you consider it's also 3 times the number of discrete channels being encoded.....

    Cheers,
    Scott
     
  10. amatala

    amatala Stunt Coordinator

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    And something more related to the downmix option:
    You shoud see this like a 'backwards compatiblity' option, a function performed by the DVD players in order to allow you to listen to the 5.1 soundtracks without loosing the surround info in case you don't have a surround receiver.
    This is not a high quality option and it will never create something comparable with the original stereo soundtrack. The original soundtrack will always sound better than the down-mixed one.
     
  11. amatala

    amatala Stunt Coordinator

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    Scott,

    It is actually 448kbits/sec not KBytes, but as I've mentioned before this is not very relevant. It is normal for a compressed format to have a lower bitrate than an uncompressed format.
     
  12. Michael Reuben

    Michael Reuben Studio Mogul

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    M.
     
  13. Scott Lawrence

    Scott Lawrence Stunt Coordinator

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    :b It would appear I was too hasty and read it wrong, you're very right, that's a lower-case b not an upper. Please disregard my previous post. :b
     
  14. Michael R Price

    Michael R Price Screenwriter

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    I think it's just the mixing and recording quality, especially the dynamic range. Isn't it much more consistent for movie soundtracks than for most music CDs?
     
  15. Kevin C Brown

    Kevin C Brown Producer

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    I have no idea what systems y'all are listening to your sources on. [​IMG] It's very simple math. DD (and DTS) are LOSSY compression algorythms. 448 kb/sec for DD vs 1411 kb/sec for CD, 6 channels vs 2. That is a lot of lost information no matter how efficient the compression agorythm is. That is actually a higher (worse) compression rate than 128 kb/sec for MP3 for 2 channels. And 192 kb/sec for MP3 is usually taken as a good "compromise" between sound quality and size. As for DTS, most soundtracks are something like 384 kb/sec. It is actually rare to find soundtracks that have been mastered at the much better rate of 768 (or so) kb/sec. I am not going to argue about DD vs DTS, that has been hashed about for years. My conclusion between those two is: mastering differences overwhelm any meaningful differences between the two codecs.

    Yes, it is not an apples to apples comparison between compression algorythms, but lost data is lost data, and no where in all the history of Laserdisc to DVD have I ever seen Dolby Digital (or DTS) mentioned as "magical" encoding schemes that somehow cheat the laws of acoustics.

    Eddie- Maybe your DVD player is lacking for CD playback, that's the only thing I can figure. [​IMG]
     
  16. Lewis Besze

    Lewis Besze Producer

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    They are far from always,the most used rate is 48/20.
     
  17. amatala

    amatala Stunt Coordinator

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    Great, so now MP3s are better than DD and DTS soundtracks.
    We are most definetly on the right track with this thread!
    I hope that people working for Dolby and DTS see this forum and can make both Dolby Laboratories and DTS see the light and give up their weak formats in favor of MP3 encoding!
    Everything should be encoded in MP3 format, even SACD abd DVD-A!
     
  18. Max F

    Max F Second Unit

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    Yeah, the first response was great and answered the question.

    I too think DD sounds better than CD (comparing what coming out of my front speakers only). Much more dynamic and clear. But maybe, i'm hard of hearing. [​IMG]
     
  19. John S

    John S Producer

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    I can honestly say I have not noticed this on my system.

    CD's sound really great weather using Analog L/R, or Optical from the player. As does DD, DTS, and even DPL as evidenced by a show on PBS where they were doing a bunch of different National Parks set to a real Symphony the other day. The soundstage and mixing was really top notch even though it was not it DD, it was just real DPL, but excellent enough to take notice. I was like man it just goes to show you, the mix down guy has a lot to do with the final product that reaches your ears.

    I think you need a better CD player. [​IMG]
    Are both sources being fed digitally? If not, try it, I'd bank it evens things up very nicely for you.
     
  20. Michael Reuben

    Michael Reuben Studio Mogul

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    That is the rate commonly referred to as "half" bitrate DTS, and almost every DTS track on DVD uses that rate. The exceptions run at twice that bitrate. Most of them were released when DTS first appeared on DVD.

    M.
     

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