DVD에 관한 거거든요.
근데 도움이 되려나…^^;;
Digital Audio Processing-Summary
“Surround Formats on DVDs – DTS vs Dolby Digital”, by Mikael Hagen and Mark Muschett, Last updated February 4, 2002, www.3dsoundsurge.com
10/22/02
Ah Ram Lee
This chapter talks about advantage differences between DTS (Digital Theater Systems) and Dolby Digital of surround formats on DVD based on some experiments. In fact, Dolby dominates the DVD market because many of DVDs use a DD5.1 (Dolby Digital 5.1) soundtrack. Just some of the concert movies hold DTS and they are not accessible in a DD5.1 edition. It means that the DTS edition of DVD movies has to be superior to compete with the Dolby edition.
Before explaining this, the article gives some explanation of DTS Digital Surround and Dolby Digital. This article provides some information about DTS and Dolby Digital in the earlier chapter of the article. It says that Dolby Digital supports up to six channels of crystal clear sound, but not all movies using a Dolby Digital soundtrack actually present 6 channels. It also explains that the LFE (low frequency effects) channel is optional for Dolby Digital. DTS is an optional channel too, and it appeared on the DVD market later than Dolby Digital. According to the DTS founder, it has a great sound quality for 16-bit linear PCM audio. The problem is that most of the DVD players are not incorporated with DTS decoder so if people want to use DTS, they have to buy a speaker system that supports DTS. “Both DTS Digital Surround and Dolby Digital use lossy compression of the original multichannel PCM sound track.” The lossy compression technology is called AC-3. The AC-3 eliminates some information that people cannot hear such as low and high frequencies. According to the article, Dolby Digital “removes up to 90% or about 3 times as much as DTS Digital Surround.” Both Dolby and DTS argue that they are more well-organized than each other and have better quality.
To take an example of one of these arguments, DTS says that ‘Dolby Digital unites channels above 15kHz at 448bitrate and above 10 kHz at 384 kbps that Dolby considers inaudible.’ According to the earlier chapter of the article, many people think that people can’t hear above 22kHz, but there are some test results which show that people still get the 96 kHz (offering 48kHz high-frequency) or 192 kHz recordings to give an advanced sound quality. Anyway, according to the authors, it is not confirmed scientifically whether DTS Digital Surround has better audible quality than Dolby Digital or not.
There is one more thing that DTS insists as an advantage – it is a discrete rear center channel (DTS-ES). However, the authors say that this system is not really helpful in most home environments.
By comparison, this article explains that Dolby Digital’s “Dialog normalization” can lessen the volume up to 8dB. This system can adjust the average centre channel volume to be between -25 and -31 dBFS (“decibels below digital full-scale”), not considering the sound source. By using this system, Dolby Digital can decrease the volume of all channels when dialogue was recorded at a higher volume, whereas DTS is weak at “Dialog normalization”.
There are some other factors that can bring different sound qualities in DTS and Dolby Digital. (for example, using different masters). Here is another example. When a DVD is being made, manufacturers want to make the DVD mix fit better into the home environment from the original movie mix because the environments of the theaters and homes are quite different.
The article says that there are some differences between DTS and Dolby Digital setting in terms of decoders (this article explains the quality differences among decoders in the earlier chapter of the article – it says that the quality of a decoder can “vary” even though Dolby and DTS guarantee their decoders and many of them use the same chip). One of the examples is a PowerDVD, which doesn’t support the LFE (low frequency effects) channel of DTS tracks. In another case, there is a Jazz Decoder that supports bass management and delay for only Dolby Digital Tracks. In authors’ opinion, the Jazz Decoder could be available for DTS tracks as well.
Up until this, this article seems to be more supportive of Dolby Digital than DTS. However, it also illustrates the good sound qualities of DTS. The authors tested some DVD movies such as Saving Private Ryan, Waterworld, Antz, the Bach edition of Naxos Musical Journey, U-571, Terminator 2 Judgment Day 2 (The Ultimate Edition) and Gladiator. The authors anticipated better managing of high-frequencies from DTS, and they found a little bit better sound quality in the Naxos Musical Journey in the DTS version compared to Dolby Digital. Nevertheless, in most of the movies they couldn’t find any sound quality differences at all. They say that the “typical multimedia speaker system” doesn’t make any sound quality differences between Dolby Digital and DTS.
However, in the last part of this chapter, the authors mention very fine-sound quality of DTS compared to Dolby Digital. According to the authors, there were some definitely audible sound quality differences in some movie scenes in DTS even on inexpensive systems. For instance, some sounds such as bullets, rockets, or explosions were much more clear in DTS than Dolby Digital, with better mixing. Further, the LFE (low frequency effects) channel worked beautifully in some movies of DTS system. The authors assume that the DTS manufacturer predicts that people would examine DVD movies with DTS Digital Surround track with great care, and judge them against Dolby Digital, and finally choose DTS .
Now I’m going to write more about the special Dolby Digital features which explained in the earlier chapter of this article. As I have noted before, the Jazz Decoder supports delay for Dolby Digital. Delay is the “the time lag between the front and the center and/or surround speakers.” By using this delay, audiences can hear sound from the front and surround speakers at the same time in Dolby Digital 5.1. – it supports the sense of being there. Of course this system might not be helpful that much in home environment, but if you have a really big room it may be valuable. They say that as far as they know, no software DVD player or soundcard offers a delay feature, though.
The other special feature of Dolby Digital is dynamic range. It is a “compression mode” and it has a really broad dynamic range between soft and loud sound. For example, when you want to hear a very loud sound and want to get a feeling of a big theater, simply using a good speaker system ,which supports loud volume well, would be enough. However, when you watch DVD at very quiet volume, the dialog would be inaudible and low-level effects might be gone. Moreover, when you happen to use the system in a big room and try to drive the amplifier/speaker too much, it can warp the system.
Compressing dynamic range is like this: keep the dialogue at the same level while you turn up the volume on quiet sound, and turn down the volume on the loud effects. The amount of the compression is already set up by the soundtrack’s producer and applied to the soundtrack. For instance, when a loud sound (which might surprise the listeners) is about to happen, the soundtrack mixers designates less compression for that sound than other loud sounds. Unfortunately, this system is not available for DTS, as the article says.
The authors tried this system in some movies, and they found that the result of enabling compressed dynamic range can differ in different movies or even in the same movie. The author says “in the loudest scene in Fifth Element enable the maximum compression only reduced the peak volume by 5-6 dB while it kept the normal dialog at the same volume. In Matrix 1 had similar results but in U-571 the peak volume was reduced as much as 12dB in one scene.”
I’ve had no knowledge of DVD before I read this article. In addition, this article was really long and hard to understand, especially some terminology and systems (however, I don’t think this article would be hard to understand for people who already know some of the DVD systems). I think I need to examine DVD movies when I happen to see some of them to experience these experiment results as I have summarized.