If PCM and TrueHD are suppose to be the same, why does PCM sound better? - High-Def Digest Forums
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Old 08-11-2007, 09:28 PM
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Default If PCM and TrueHD are suppose to be the same, why does PCM sound better?

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Originally Posted by blu-ray.com (review of the Fifth Element)
In theory, these tracks should sound the same, but the reality of the situation is somewhat different. For whatever reason, I found the PCM track to be much more robust. There is a slight variance in volume between the two tracks, with the TrueHD track being slightly softer. Once volume corrections had been made, the PCM track was still superior in many ways. In addition to the aforementioned richness and intensity of the PCM track, I also found dialog to be a bit more crisp and the entire surround soundstage more enveloping with PCM. I have no idea why this might be the case, and it remains to be seen on future release whether this disparity shows up again. But, in the case of The Fifth Element, I definitely recommend sticking with PCM. It should be noted that Dolby’s notorious Dialog Normalization is not active on Sony Blu-ray releases, so this would not account for the slight differences in the two soundtracks.
http://www.blu-ray.com/movies/movies...56&show=review

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Originally Posted by blu-ray.com (review of 300)
Some HDTV fans are excited by Dolby TrueHD. I have been to Dolby Labs in San Francisco where I was invited by a friend from Sony Singapore to compare the TrueHD and PCM content of a promotional blu-ray disc. We heard a difference that audiophiles would describe as a more realistic resonance with the PCM. The instruments reproduced using TrueHD had less bloom, but on low-end systems, this may come across as an advantage, so I am reluctant to criticize Dolby TrueHD. Those with golden ears and a reference quality system will definitely want to opt for PCM, though.
http://www.blu-ray.com/movies/movies...51&show=review

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Originally Posted by highdefdigest.com (review of the Departed)
Now, how do the PCM and TrueHD tracks compare? Given this historic opportunity, I decided to conduct a little experiment. I invited a friend over, who is a big movie and music buff, but not particularly technical. He knows good audio when he hears it, yet doesn't know a PCM from an RPM from R.E.M. In other words, he's Joe Six-Pack with a great ear. Anyway, together we conducted a "blind" audio test -- we select ten short sequences from the film, and listened to a compare of each. We took turns firing up each scene, and selecting which one sounded better, with no knowledge of which sample was the Blu-ray and which the HD DVD.

After writing down our answers on little scraps of paper (note that we didn't throw them into a hat -- we aren't that dorky), the results were interesting. Out of the twenty comparisons (ten for him, ten for me), we could only detect differences on four scenes total. But of those four, we both always preferred the PCM track, if only a smidgeon. For example, there is a scene in involving an attempted trade bust between the Costello character and a Chinese gang. There is a sound of a gun firing that we went back over a few times, and as silly as it sounds, the force and impact of the sounds was a shade more realistic in PCM. Also a beneficiary of the uncompressed mix is the music, as this is a film brimming with rock songs. The first scene we picked featured the Rolling Stone's "Gimme Shelter," and again the PCM track boasted a slightly more spacious feel to the music in all channels -- as if the very highest end of the frequency range was more palpable.

Granted, these are very slight differences and subjective preferences. Had we not blindfolded each other (figuratively speaking, of course) and been flipping back and forth between discs like one of those old Coke-Pepsi commercials, such deviations likely would have been imperceptible. It is also certain that the average listener wouldn't be able to tell the difference without possessing the ears of a dog. Still, in this case I give a slight edge to the PCM track, though a comparison between a single title hardly qualifies as the final word. If nothing else, it made me realize that if all the studios dumped this dueling audio format business and went all-PCM, I can't say I would be likely to complain...
http://bluray.highdefdigest.com/departed.html

Quote:
Originally Posted by highdefdigest.com (review of 300)
Right upfront, the PCM sounded a bit louder, but after some level matching, a direct A/B comparison of several scenes revealed only slight differences.
http://bluray.highdefdigest.com/300.html

I am not anti TrueHD as I really like the idea of not having lots of space taken up on a disc by PCM. Both PCM and TrueHD are in theory supposed to sound exactly the same but in reality this has shown to not be the case. Maybe companies like Warner and Sony know something we do not. Why include both the TrueHD and PCM soundtracks on Blu-ray titles like 300 and the Fifth Element? Maybe someone can explain from a technical view why a TrueHD soundtrack is not the equal of PCM.
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Old 08-11-2007, 09:53 PM
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I think it's all relative to yourself and your system.

I think DTS sounds better than DD5.1.
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Old 08-11-2007, 09:55 PM
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Dobyblue - where are you when we need you?
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Old 08-11-2007, 10:10 PM
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They do sound the same. Any difference is in the imagination of the listener.

The fatal flaw in these lossless algorithms is the transport from the player to the receiver. If you have a Blu-ray or HD-DVD player that outputs analog... you lose all quality offered by lossless. This is due to the extra analog-to-digital step:

Player (D-to-A) --> Analog signal over coax --> A-to-D in receiver --> DSP filtering in receiver --> D-to-A amplification in receiver

It is better to have digital transport:

Player (digital) --> HDMI --> D-to-A amplification in receiver

Only then would lossless (DTS-HD MA, TruHD, PCM) be able to shine. The signals output would be bit-for-bit exactly the same. Any difference would be a flaw in the receiver.
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Old 08-11-2007, 10:11 PM
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I had heard a term in one of the other forums called "dialog normalization" or something along those lines...if the studio turns sets the feature on, it can make the TrueHD track not sound as good as the uncompressed. If the studio leaves it off, however, the tracks should in theory be identical. I wish I knew more!

Also waiting for someone to explain more fully...
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Old 08-11-2007, 10:18 PM
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Quote:
Originally Posted by pkremer View Post
I had heard a term in one of the other forums called "dialog normalization" or something along those lines...if the studio turns sets the feature on, it can make the TrueHD track not sound as good as the uncompressed. If the studio leaves it off, however, the tracks should in theory be identical. I wish I knew more!

Also waiting for someone to explain more fully...
The ol' saying: garbage-in garbage-out applies here. If the studio messes with the audio before encoding... well... That isn't the fault of Dolby or DTS!
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Old 08-11-2007, 10:37 PM
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Quote:
Originally Posted by Treadstone View Post
I think it's all relative to yourself and your system.

I think DTS sounds better than DD5.1.

Agree, this is very subjective stuff here.
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Old 08-11-2007, 11:35 PM
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This reminds me. WHY do some single layer BD's use PCM while it seems almost NO dual layer HD DVD's do? It seems to me if space was such a concern then why are some BD people using a space hog like PCM on a single layer instead of TrueHD?
edit: I have a suspicion it's because these companies are too cheap to pay Dolby the royalty fee's for using their Lossless codec.
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Old 08-11-2007, 11:40 PM
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Quote:
Originally Posted by pkremer View Post
I had heard a term in one of the other forums called "dialog normalization" or something along those lines...if the studio turns sets the feature on, it can make the TrueHD track not sound as good as the uncompressed. If the studio leaves it off, however, the tracks should in theory be identical. I wish I knew more!

Also waiting for someone to explain more fully...
it makes it sound "not as good" because it is a feature designed to allow the dolby tracks on one disc to all be at the same levels as each other

when you reduce the levels of a lossless track it still remains lossless, but the overall dynamic is affected because the higher the volume levels the greater the dynamic

for example the cd has a maximum of around 94db, whereas an sacd has 120db

combined with the far superior data delivery and greater dynamic range sacd easily wins out over cd

in the case of truehd the only thing that changes is the dynamic range by reducing the levels to match those of the other dolby tracks - by turning the dn off you allow the same dynamic range as the original pcm track and therefore there is no difference

as long as dn is not used the most important thing becomes bit depth and then secondarily sample rate, so a 24-bit truehd track like the one upcoming on spider-man 3 will be substantially superior to the 16-bit pcm track on said disc (sony sets dn to -31 which turns dn off)
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Old 08-11-2007, 11:49 PM
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While watching 300, I watched some of the scenes in PCM and again in Dolby TrueHD and thought the PCM sounded better. This is not what I expected at all, and I don't have an expensive system either, but I deffinately could tell a difference.

PS. I too prefer DTS over DD.
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