why do Dolby Digital sountracks sound so GOOD? (1 Viewer)

[Lewis Besze]

Relax, he didn't suggest that, he only said that the compression rate per channel is higher on DD thatn MP3 at 128kbps,simply because DD has 6 channels to deal with.However since two different codecs can't becompared on comression ratio alone so I wouldn't worry about it. I do think that DD is a better codec then MP3.

 

[Kevin C Brown]

Ok, so some please explain to me why a LOSSY compression format is going to sound *better* than CD?

Both DTS and DD are encoded on DVDs with PCM. That is the same as CD. So saying that CD technology sucks because it's 25 years old is ignorant.

So OK, DD is encoded mostly at 20 bit/48 kHz. The 48 kHz is only 10% higher rate than CD's 44 kHz. That higher rate mostly just gets you higher freq response, from 22 kHz to 24 kHz. Most people can't hear above 18 kHz or so. Plus, compression algorythms have a harder time at high freqs because there's more information there. ... So the higher freq sampling rate is MEANINGLESS in the real world.

So yes, now let's look at word length. 20 bits vs 16. This gets you higher dynamic range, or, a higher signal to noise ratio. But, take a look at some interesting real world measurements:

http://www.soundandvisionmag.com/art...ber=3&preview=

Sony DVD/CD/SACD player. Dolby Digital measures worse than CD even though are both limited to 16 bits! One more, a $2400 H/K receiver:

http://www.soundandvisionmag.com/ass...AVR7300lab.pdf

DD again comes out about 75 dB (limited to 16 bits though). But so does CD (stereo, digital input). And, see the "excess noise" number? That means the hardware itself is limiting the s/n (and dynamic range) to substantially less than the theoretical for 20 bits.

And ... how many of you who actually think that DD sounds better than CD, listen to DVDs at reference level, 0 dB? Not many, right? (I listen at normally -10 to -15 dB.) Well ... to actually get the full benefit of those 20 bits (as if it existed in the first place) you'd have to listen to your DVDs at 0 dB. That's right. Otherwise, you are artificially limiting the signal to noise ratio of your system.

One additional factoid not many of y'all might be familiar with. What the noise level in the average home is. I've seen measurements that real world measured signal-to-noise ratios are only on the order of 50 to 60 dB. A/C, heating systems, traffic noise, refrigerators, fans, etc. (Shoot, I just got a new DVR from the Dish Network that's bugging me because I can hear the stupid hard drive...) Some people with dedicated home theaters and sound treatments as well as sound insulation obviously do better. But the average home? 50 - 60 dB.

So what have we just seen? That the 20/48 or even 24/48 for Dolby Digital soundtracks in meaningless in the real world.

So we are still left with ... compression. For those mathematically challenged:

1411 kb/sec for CD (2 ch): 706 kb/sec/ch, 16 bit word => 44 words/sec/ch
448 kb/sec for DD (6 ch): 75 kb/sec/ch, 20 bit word => 4 words/sec/ch

20 bit word lengths actually makes the ratio worse for DD. You wouldn't need as much compression if 16 bit word lengths were used.

So again, someone please explain to me how squashing the data rate to that large an extent can *improve* the sound quality? No matter how good the compression scheme is? Eddie, either you need better CD playback, or, maybe you just need to listen to some better mastered CDs...

 

[David Judah]

You're right it can't. There are so many variables in Eddies comparison, it's meaningless--different sources, material, receiver input settings, etc...

My guess, Eddie, is you are equating the greater amount of bass(especially if you have your sub pumped up higher in level relative to the other channels)from movie soundtracks to a fuller, richer sound. When you switch to a CD in direct mode, the bass will lack in comparison(although it is not necessarily less accurate). Concentrate on the mids & highs(especially cymbals).

Or maybe there is something to that psycho-acoustic masking after all.

DJ

 

[Max F]

That's likely my problem (not speaking for Eddie). Don't get me wrong, i love my CD playback through my Sony CE595. It's just that the music on some DVDs sound more dynamic and clean, likely due to the better recording or the volumes that i'm listening to.

So, basically, if i watch a concert DVD i should use the standard stereo PCM because that will produce better quality sound than DD?

Damn, i wish SACD would catch on more. Now i know that sounds better. Pink Floyd's DSOTM sounds fantastic on my system.

 

[John S]

Hmm Concert DVD's, I try it both ways often times.

Sometimes the DD/DTS is best, sometimes stereo is best.

I really think it comes down to the mixing engineer more than anything else.

 

[eddieZEN]

Kevin,

> Eddie, either you need better CD playback, or, maybe you just need to listen to some better mastered CDs...

Yup, could be both in fact. :frowning:

Actually what I'm going to do tonight or tomorrow is a little experiment: play the same track from the DVD of "The Hours" and then the same track on the CD soundtrack of it.

I also tend to agree with John S, attributing it to the mixing engineer.

And after my next upgrade (a SVS or Hsu sub) I may start looking around for a better CD player in the $200-500 range, the modified Toshiba at referenceaudiomods.com comes to mind...

 

[AlbertA]

I do research on the field of data compression.

It's a well known fact in Array Signal Processing (Audio) that sampling at a higher rate, with more dynamic range, and compressing to yield the same data rate that a lower sampling, lower bitdepth process is much better (objective metric functions wise).

But what probably I would think in this case it's probably just a better mastered source.

If we had the same source, and then convert it to PCM 16 bit, 44100Hz, and another compressed to 48Khz, 24 bit, then I can tell you (objectively) which one is better. But we probably won't have access to those sources, so we can't say.

 

[Lewis Besze]

Many processors use DSP chips that are "floating point" design which means it will deliver the full bit processing at any volume or output.These are mostly 32 or 44 bit rate chips so they have no problem to accomodate the mere 16/20 bits of DD and DTS. Just FYI

 

[Kevin C Brown]

Good to know. That was always a question a buddy of mine had. (Hey Lewis, another question you might know. S&V numbers for 16 bit are about 75dB. But I always thought theoretical s/n for CD was more like 96 dB, and for DVD-A at 24 bits, it was something astronomical like 120 dB. A good turntable in the 70's could easily do mid 70's for s/n. ??)

I did notice that over on AVS, mastering is the general consensus responsible for the differences heard between DD and CD too. Movie soundtracks are mastered to have impact in addition to the visuals, but for CD, the audio just has to stand on its own. So maybe movie soundtracks are more "forcefully" mastered because the audio has to compete for your attention with the video. One though, anyways.

 

[David Judah]

Thanks for the info., Albert. Could you please expand a bit on the criteria used for objectively determining which is better in the type of comparison you mention? I'm curious about that.

DJ

 

[Shiu]

I am not sure if are joking or not, I take this seriously. My experience is that if I use my C$115 DVD player, DD, DTS movies sound superior to my CDs. If I use my 3 year old C$250 Sony DVD player, DD & DTS movies sound about the same as CD in terms of overall sound quality. If I use my Denon 3910, the reverse is true, CDs sound better than DD & DTS movies. I never understand why this is so, but it is true, and obvious enough that I am sure anyone who listened to my 3 players would agree with my observation.

 

[John S]

All connected digitally to your processor Shiu?

I am a little surprised. But anything is possible for sure.

 

[Shiu]

John,

With the cheap DVD player - Optical
The Sony NS725P DVD player - Coax
Denon 3910 - DLink

I also have a 3 year old mid level Panasonic DVD player, same thing, sounded decent with DVD's but not too good with music CD's, much worse than my 20 year old top of the line $2K Kenwood CD player. The CD player beat them (except for the 3910) easily in either coax, optical, or analog.

I usually listen to CD's using Stereo, or Direct. Without knowing why, I was forced to conclude long time ago that entry level DVD players cannot do justice to CD's.

 

[John S]

Interesting... You would think, allowing the AVR to do the D to A, nearly all digital sources would be so close to identical to be inpercievable.

Thanks for the additional information.

I do still reccomend dedicated CD players for most people.
I don't even think I have tried a CD in my LD or DVD player, I have Sony 300 disc changer connected by optical myself. Seems to sound great, using the Burr-Brown Dacs in the Denon 4802 AVR.