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Old 10-15-2007, 12:24 AM   #1
stockstar1138 stockstar1138 is offline
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Apr 2007
Default PCM vs. Dolby TrueHD

Some idiot is trying to tell me that PCM and Dolby TrueHD sound exactly alike. Can somebody please provide me with a link to prove him wrong. He's quoting Bracke over at HDD, a known idiot.
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Old 10-15-2007, 12:34 AM   #2
jorg jorg is offline
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i didnt know there were links to obv things it like saying being dead and in a commom are in the same thing
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Old 10-15-2007, 12:46 AM   #3
Scrapanatchi Scrapanatchi is offline
Aug 2007

it's extremely hard not to say imposible to actually hear any diffences especially if the orginal source is decent. a blindtest wouldn't do much good either sence a compressed source usually cut unecsesary sound peaks which an uncompressed pcm doesnt i would say it saves disc space and sound almost identical...
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Old 10-15-2007, 12:50 AM   #4
BStecke BStecke is offline
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Really, there shouldn't be any difference, but sometimes there is. For instance, a higher bitrate TrueHD track will sound better than a lower bitrate PCM track. Once uncompressed, TrueHD should sound exactly like the master.

There are approximately 1 billion threads on this topic, as well . . . a search will turn up a lot.
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Old 10-15-2007, 12:53 AM   #5
bluseminole bluseminole is offline
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Originally Posted by stockstar1138 View Post
Some idiot is trying to tell me that PCM and Dolby TrueHD sound exactly alike. Can somebody please provide me with a link to prove him wrong. He's quoting Bracke over at HDD, a known idiot.
For all intensive purposes, most people--even those with critical ears--couldn't tell an audible difference. Perhaps if you have tens of thousands of dollars invested in equipment and exceptionally nice speakers, the differences could be heard, but even on some modestly advanced systems, the differences are just negligible.

I did notice, however, that between the PCM and TrueHD track on 300, the PCM was much louder than the TrueHD track, which gave it the impression of being a lot better. However, just bumping the volume up on the TrueHD track and then switching back and forth, there was no difference in quality--just volume.
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Old 10-15-2007, 01:37 AM   #6
Brain Sturgeon Brain Sturgeon is offline
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Sep 2007

I posted this about the PCM v. THD thing in a similar thread:
Bit for bit, PCM and TrueHD, assuming both are from the same master, theoretically should be the same. But, unless the audio encoder set the audio attenuation on the encoder to -31dB (instead of its default: -27dB), then Dialogue Normalization (set at -4dB at default) will have been applied to the soundtrack during the TrueHD encoding process and the soundtrack is no longer identical to the studio PCM master. Now, whether DialNorm is a bad thing or not is a controversial subject, but assuming that the original studio master is the best representation of the desired audio for the movie, then any modification of that, even if it is as simple as a -4dB attenuation of the center dialogue channel, would seem to be a detriment. And it does not appear to be as simple as a volume issue.

A quote by DaViD Boulet from an AVS thread:

"the problem with DN isn't that it lowers the dynamic range (volume) by 4 (or more) db... the problem is HOW it does it.

It does it by digitally recalculating the audio data to digitally down-scale the waveform.

That means that you will NEVER get bit-for-bit accuracy from a TrueHD stream that's been flagged with dialog-normalization.

And it can't be bypassed because Dolby won't allow any in-spec consumer gear to let the user avoid it! It doesn't matter that it's just a meta-data instruction flag: if Dolby REQUIRED that it's processing instructions be followed by your decoder, then the fact that the original PCM lossless data was represented prior to DN processing is moot."

So unless DialNorm is defeated during the TrueHD encoding, then it is not the same as the studio master.

I'd take the PCM over TrueHD unless the dialnorm flag has been defeated. If it has, then the two tracks should be theoretically identical. I have not, as of yet, had a chance to compare a PCM track to a TrueHD track where DN was defeated, so I can't give my opinion as to whether this bears out on "real world" listening.

If this does bear out and both sound identically good, then it makes sense to use TrueHD without DN over PCM, as TrueHD would allow anywhere from a 2:1 to 4:1 compression of data without loss of quality, leaving us more room for higher bitrate video (assuming bandwidth is available), extras, etc...

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Old 10-16-2007, 12:10 AM   #7
Clark Kent Clark Kent is offline
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Oct 2007

Warner titles do use dialogue normalization on Dolby TrueHD encodes, meaning that their tracks are slightly inferior to their PCM counterparts(another reason to buy the Blu-ray version over the HD-DVD version of Warner movies).

PaidGeek wisely got Sony to not use dialogue normalization on its Dolby TrueHD tracks, meaning that their Dolby TrueHD tracks(like on Ghost Rider) are mathematically identical to the original PCM track if the bitdepths are the same.
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Old 10-16-2007, 12:23 AM   #8
gvortex7 gvortex7 is offline
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I've posted this already in another thread, but I'll say it again.

Using the remastered Fifth Element as a perfect example since it has both PCM and Dolby TrueHD, I though PCM blew TrueHD away. It was a lot more dynamic sounding with my audio setup. I was switching back and forth between the two options for about 15 minutes, but the difference in quality was apparent from the get go.

I haven't checked the bit rates for either encoding format on The Fifth Element, but to me PCM was the clear winner.
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