CD's vs LP's vs DVD sound tracks.

[Fla Ann]

I am new to this site so please bear with me. I have noticed that the music tracks on DVD's sound far better than the same song tracks on a CD. Why is that and why can't the CD labels get that same sound on a typical CD ???

JRD

[Brandon B]

Care to cite s specific movie you found this to be true? Not sure how you can judge how good a soundtrack sounds with all the incidental sound FX, foley and dialog over top of it.

BB

[kirknelson]

Dolby Digital and DTS are different digital compression algorithms than CD uses. They use less compression, have higher dynamic range and a higher sampling rate than CD has. All of this contributes to a "better" sound but whether or not that holds up depends on the mix.

[Kevin D]

CD's don't use any compression at all and the sampling rate isn't higher enough to make a difference. So in theory CD should sound way better.

The problem you are running into is most likely how the composer wanted it to sound on CD, versus how the movie editor wanted it to sound in the movie.
You also have to consider that the DVD will be mixed properly for 5.1 sound while you may only have 2 speakers playing the CD or at most a processed 5.1 sound.

Kevin D.

[kirknelson]

CD's don't use any compression at all and the sampling rate isn't higher enough to make a difference. So in theory CD should sound way better.

That's not true. You may not be decompressing the audio track at the time of play back but the audio was highly compressed at the time of recording. This is the whole reason we have the LP vs. CD debate. LP "could" have higher resolution (if resolution could be defined for an analog medium) than CD. This is also the reason why the new audio formats SACD and DVD-A came about.

SACD is the only digital source that could claim to be uncompressed and have a leg to stand on.

[kurtholz]

I don't think that is exactly right,as DVD-A has a very wide soundstage and is in my opinion a completely different sound than SACD, i think most who have both will agree DVD-A is more analog like, without the pops and hiccups of vinyl

I'm sure everyone will agree with me

:-)

Kurt

[Brandon B]

That's not true. You may not be decompressing the audio track at the time of play back but the audio was highly compressed at the time of recording.

No it was not compressed. It was sampled, at a given frequency and with a given dynamic range. But it was not compressed in the sense we are talking about here, which is taking the digital data and reducing the bandwidth required by discarding some of the data.

DVDs, which typically feature the same music from the same recording sessions, have been mixed and processed differently, and then compressed into either a DD or DTS track (generally). CDs contain the music mixed and mastered for a 2 channel presentation, but no compression takes place. The differences the poster is hearing are a result of the different mixing and mastering process, as well as the settings and processing of their system and how that varies for 5.1 vs. 2 ch program material.

BB

[kirknelson]

No it was not compressed. It was sampled, at a given frequency and with a given dynamic range. But it was not compressed in the sense we are talking about here, which is taking the digital data and reducing the bandwidth required by discarding some of the data.

Imo, the sampling rate can be counted as compression. You are still throwing out data. Since DD and DTS have a greater sampling rate they keep more of that information. Whether it is then lost through the compression -> decompression is up for debate and is largely a factor of how good the DACs are. Yes *some* information is lost as it is a lossy compression format but whether it is enough to reduce the quality to or below that of CD is debateable. In my own subjective experience DVDs (not just limited to movies but also concert and music DVDs) sound better than CDs.

DVDs, which typically feature the same music from the same recording sessions, have been mixed and processed differently, and then compressed into either a DD or DTS track (generally). CDs contain the music mixed and mastered for a 2 channel presentation, but no compression takes place. The differences the poster is hearing are a result of the different mixing and mastering process, as well as the settings and processing of their system and how that varies for 5.1 vs. 2 ch program material.

Ok I see your point. However, the higher sampling rate would still impart higher resolution as noted above. Movie sound tracks are encoded from the original masters (which is mostly DSD, otherwise known to consumers as SACD) not from the CD audio derivatives of the masters.

Also many (Star Wars, LoTR, Saving Private Ryan, Brokeback Mountian, etc.) actually recorded the orchestral selections using a 5 channel mic set-up. So the musical scores were not mixed, they were layed down in 5.0. Actually, it is becoming standard practice for movies with an original score to record it in 5.0.

[Brandon B]

Imo, the sampling rate can be counted as compression. You are still throwing out data. Since DD and DTS have a greater sampling rate they keep more of that information.

OK. To me "has the same net effect as" and "means the same as" are not equivalent statements, hence my argumentativeness.

BB

[kirknelson]

Understood. :T

You had some good points though too and I didn't think we were argueing so much as expressing different opinions. In the end audio is completely subjective after all.

[stantheman2]

Another viewpoint...

A little thought and web surfing on this subject gives the following (simplified, of course):

Analog audio via LPs is hypothetically "lossless", but mechanical and electrical limitations modify the signal, so losses do occur.

CDs are mathematically "lossless", because the sampling frequency at 44,100 samples per second (44.1 kHz) is over twice the typical high-frequency hearing limit of 20,000 Hz (20 kHz). However, most audiophiles believe some audio quality is lost in a CD.

When looking at digital recording, the fundamental question is "How much information does the digital data stream convey?" The information is digital bits, and information is transferred by the bit rate, or bps.

The CD bit rate is 44,100 samples per second times 16 bits per sample times two channels, or 1.41 million bits per second (Mbps). That is 705,600 bits per second per channel, or 705.6 kbps per channel.

Now, Dolby Digital's bit rate is 384 kbps to 448 kbps, for 5+1 channels, or 64kbps to 74.7 kbps per channel. DTS's max bit rate is 1.5 Mbps, or 250 kbps per channel. Both Dolby Digital and DTS use what are defined as "lossy" compression systems - that is, they DISCARD SOME OF THE AUDIO INFORMATION BY THEIR DESIGN. They do employ variable bit rates and complex algorithms to lesssen the loss (psychoacoustically), but DTS, at its best, only transfers as much total audio information as a CD, but at a lower rate per channel of audio information than a CD.

DVD-Audio and SACD improve upon the above. DVD-Audio's maximum bit rate is 9.6 mbps, or 1.6 Mbps per channel (5.1). So, DVD-Audio, at its best, coveys almost seven times as much audio information as a CD. SACD uses a fundamentally different approach - sampling a 1-bit signal at 2.82 million times per second, or 2.82 Mbps. However, since the underlying technology is different, SACD delivers about as good a perceived audio quality as DVD-Audio.

HD-DVD and Blu-Ray, as I understand it, can have audio information transfer rates on a par with DVD-Audio.

[Chris D]

Wait... are you comparing the sampling rate of CD's to an audible tone frequency?

[Brandon B]

He is, and there is an important relationship there. It has to be high enough to not only capture the upper limit audible by humans, but also avoid aliasing effects at those frequencies.

BB

[stantheman2]

Yes, that early section in my post was comparing audio frequency to the sampling rate of a CD. What I was referring to was a mathematical concept (the Nyquist theorem??) that states that as long as the sampling rate for digital conversion is at least twice the maximum frequency of the signal that is sampled, the analog sound signal that is reconstructed will be an exact replica of the original analog signal. I'm not a mathemetician, but I don't buy it. Look at it simply: a 20,000 Hz sine wave starts at zero level, goes up, then down (crossing through zero and going negative), then back up to zero, and repeats that process 20,000 times a second. Now sampling at 40 kHz (twice the frequency) cannot reconstruct that sine wave. If the samples are taken at the points in time when the signal crosses zero, the two smaples would be zero and the result would be no signal reconstructed at all. If the samples are taken at the positive peak and the negative peak, the reconstructed signal would be a saw tooth graph, not a sine wave. In either case the recoonstructed signal would look absolutely nothing like a 20,000 Hz sine wave. That is why a higher sampling rate (IMHO) is necessary to have any real hope of accurately reconstructing high aduible frequencies.

Note I am NOT talking about "oversampling" standard CDs. A CD contains 44,100 samples per second. Four rimes oversampling, or sampling 176,400 times per second, only samples the same information four times. That reduces the potential error in reading the sample, but doesn't create more information. What I'm talking about is more than 44,100 different signal samples per second.

[Chris D]

The Nyquil theorem: Drink enough alcohol, and everything sounds the same. (and looks better!)