Video Asylum

Re: Lossy compression - how much is really "lost"?

128.152.20.33

[ Follow Ups ] [ Post Followup ] [ Thread: Display Email ] [ Video Asylum ] [ FAQ ]

In Reply to: Lossy compression - how much is really "lost"? posted by John C. - Aussie on July 25, 2002 at 18:57:37:

Not sure if I can help here, but I do knwo there is a book called
"The COmpression Book" (boring title!) that I have used. It covers the general topic of compression, lossy and non lossy, and goes into great detail on the history of compresison methods, up until when the book was latest revised. It's a great primer if you really want to understand the subject. I don't know if the latest version covers AC-3, but there are alot of books that do, if you look hard enough.
ciao
Doug

Follow Ups:

Thanks for the reply Doug but .... - John C. - Aussie 00:40:37 07/27/02 (5)
... what I'm really after is an opinion on the subjective appraisal of the loss. I'm guessing it might be a bit like the watermarking on DVD-A's. Everyone hates it yet few seem to be able to hear it!
My point is we are living happily with lossy stuff on video - the eye rarely detects any loss. The question is can the ear really detect the loss in AC3 & DTS and if it can what makes the loss obvious?
John

Peace at AA
- DD ok for movies, not music - Lasermeister 04:54:40 07/29/02 (0)
  My opinion is that while Dolby Digital works fine for action movies and stuff like that, it doesn't work as well for music intensive material as does PCM. I find that music sounds less warm and musical on Dolby Digital compared to PCM, but the advantage of DD's 5.1 channels is viewed as so much of an advantage over Pro-Logic PCM that its audio shortcomings wind up never being discussed much anymore. But perhaps I'm just an old crank.
  Todd
- Re: Thanks for the reply Doug but .... - Dave 13:37:00 07/27/02 (3)
  Dolby Digital typically packs the audio for an entire two-plus hour movie on DVD in one-quarter of the space used to master an uncompressed PCM CD. The loss varies according to program content, but can be be as great as 75% in many places. The DD bitrate is slightly higher on LD than DVD - try listening to the same material in both formats, you should hear a significant improvement with LD, especially in respect to "venue" or the ambient sound of the recording.
  Meridian has been pushing for some time to implement their propriatary "MLP" lossless packing codec which can handle playback at rates of 16.44 24/96 on DVD with zero data loss and can go as high as 24/96 lossless (with some program time limitations) on dual-layer discs. It's a far better system in both theory and practice but so far Meridian has not be able to topple the Dolby Labs juggernaut.
  If you have a processor with a pure analog pass-through, try playing a DVD encoded in pure PCM - it should sound superior to even the very best LD AC-3 replay. Ditto for dedicated Dolby 2.0 surround audio tracks (just be sure it isn't a 5.1 mixdown) - the bit rate only has to handle two channels instead of 5.1 and thus the signal is more robust.
  BTW, if you really want to have fun, try cueing up a 5.1 DVD-Audio soundtrack with the DVD video - it's a mind-blowing experience. High-end HT rules!
  - Re: Thanks for the reply Doug but .... - Max 15:34:46 07/27/02 (2)
    The DD bitrate is slightly higher on LD than DVD - try listening to the same material in both formats, you should hear a significant improvement with LD, especially in respect to "venue" or the ambient sound of the recording.
    Actually it's the other way 'round. The maximum DD bitrate on DVD is slightly higher than LD (448K vs. 384K)
    - Same anomolies exist with DTS . . . - Auricle 07:44:59 08/01/02 (0)
      Though DVD can have a higher rate than LD, it virtually never does. In general, I find the sound of DTS on Laser much better (and I do mean much) than DVD.
      As for DD, on many Lasers I find myself choosing the Dolby Surround track, simply because it has less irritating timbre modifications.
    - Re: Thanks for the reply Doug but .... - Dave 17:36:38 07/28/02 (0)
      ---> The maximum DD bitrate on DVD is slightly higher than LD (448K vs. 384K)
      Technically correct, however, only a few music-oriented DVDs like James Taylor Live at the Beacon are mastered at 448K bit rate - almost all 5.1 movies are 384K bit rate. Mono movies on DVD can be mastered as low as 91K bit rate (Gary Reber's "thin, compressed mono") and 5.1 downmixes are typically 256Kb. LDs always use the full 384K bit rate and are processed internally at a full 20 bits with 16/44 output instead of DVD's 18 bit internal -16/48 output which gives subjectively better sound.
      Numbers aside and all things being equal, LDs sound better than DVDs when replaying 5.1 DD surround.

This post is made possible by the generous support of people like you and our sponsors:

Atma-Sphere Music Systems, Inc.

You can not post to an archived thread.