Uncompressed PCM 5.1 Surround vs. Dolby TrueHD 5.1 / Can you "HEAR" a difference? - AVS Forum
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post #1 of 37 Old 08-29-2007, 11:36 AM - Thread Starter
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Blu-ray fans this thread is for you. I want to know if anyone can tell the difference between the two. The movies 300, Fifth Element(remastered), Ghost Rider, and Stomp the Yard all have both soundtracks. All excellent demo material. Let's talk about it...

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post #2 of 37 Old 08-29-2007, 11:48 AM
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Quote:
Originally Posted by kemiza View Post

Blu-ray fans this thread is for you. I want to know if anyone can tell the difference between the two. The movies 300, Fifth Element(remastered), Ghost Rider, and Stomp the Yard all have both soundtracks. All excellent demo material. Let's talk about it...

There is no difference. After you decode the TrueHD track, it is 5.1 PCM.

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post #3 of 37 Old 08-29-2007, 11:51 AM - Thread Starter
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Quote:
Originally Posted by littlesaint View Post

There is no difference. After you decode the TrueHD track, it is 5.1 PCM.

But can you HEAR the difference?

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post #4 of 37 Old 08-29-2007, 12:06 PM
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Quote:
Originally Posted by kemiza View Post

But can you HEAR the difference?

What "difference" are you talking about? TrueHD is PCM 5.1 stored more efficiently. They're bit for bit identical. Since there's is no difference, you can't hear something that's not there.

Sanjay

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post #5 of 37 Old 08-29-2007, 12:07 PM
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Quote:
Originally Posted by kemiza View Post

But can you HEAR the difference?

If there's no difference, why would I hear a difference?

I guess my simple answer to your question is no, I do not hear a difference, but I qualify that by saying there shouldn't be a difference to hear.

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post #6 of 37 Old 08-29-2007, 12:17 PM
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There is no difference....which is why it is so dumb that Blu-rays are being mastered with PCM tracks instead of TrueHD (even more dumb is Fox insisting on releasing titles with the only lossless track being a format not supported by a single player).
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post #7 of 37 Old 08-29-2007, 12:42 PM
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There is no difference. Unless when you write "PCM 5.1" you're really thinking of DTS or Dolby Digital 5.1 converted to PCM by the player.
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post #8 of 37 Old 08-29-2007, 12:44 PM
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OP- Did you mean DD 5.1 vs. TrueHD 5.1?
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post #9 of 37 Old 08-29-2007, 12:50 PM
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I wish bluray-1080p would get in on this one. So very entertaining he makes it! One could totally agree with what he says and he would still argue and say "hahaha you're wrong and stupid and I'm always right.
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post #10 of 37 Old 08-29-2007, 01:46 PM - Thread Starter
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Has anyone done an A/B comparison with Ghost Rider?

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post #11 of 37 Old 08-29-2007, 02:10 PM
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A particular title may have mastering differences between thr PCM and TrueHD tracks, but it is not due to differences between TrueHD and PCM, it is the encoding choices made by the studio; that is volume levels, dynamic range control, bitrate, etc. These are set independently of the audio formats themselves and up to whom ever is encoding the audio.

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post #12 of 37 Old 08-29-2007, 02:42 PM
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kemiza, do you know what it is that you are asking? Or not?

Could we have some clarification, please?

I would direct you to Post #8 of this thread.

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
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post #13 of 37 Old 08-29-2007, 07:55 PM
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one is the lossless compressed version of the other, right?

So, if there's any real sonic difference, something is broken.
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post #14 of 37 Old 08-29-2007, 07:57 PM
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Here's a thought. Decoded TrueHD is bit for bit identical to PCM 5.1 if the decoder makes no errors and has no drop-outs. Is there any chance that there is some level of error rate? I assume that low levels of errors would be covered by perfect error correction. But higher error rates and drop-outs would need to be concealed by interpolation. Hence there might be some level of bit discrepancy between the two and possibly audible under careful listening conditions.

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post #15 of 37 Old 08-29-2007, 11:54 PM - Thread Starter
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Quote:
Originally Posted by littlesaint View Post

A particular title may have mastering differences between thr PCM and TrueHD tracks, but it is not due to differences between TrueHD and PCM, it is the encoding choices made by the studio; that is volume levels, dynamic range control, bitrate, etc. These are set independently of the audio formats themselves and up to whom ever is encoding the audio.

This is a very valid point. Thank you.

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post #16 of 37 Old 08-29-2007, 11:55 PM - Thread Starter
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Quote:
Originally Posted by ekb View Post

Here's a thought. Decoded TrueHD is bit for bit identical to PCM 5.1 if the decoder makes no errors and has no drop-outs. Is there any chance that there is some level of error rate? I assume that low levels of errors would be covered by perfect error correction. But higher error rates and drop-outs would need to be concealed by interpolation. Hence there might be some level of bit discrepancy between the two and possibly audible under careful listening conditions.

Ed

Another valid point. Thanks ekb.

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post #17 of 37 Old 08-30-2007, 12:32 AM - Thread Starter
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A very reputable person in the audio/video world told me you can hear a difference between the two soundtracks. He played Ghost Rider on a PS3 & a Yamaha 1.2 receiver, using Klipsch reference speakers. He said the sound was identical on the high end but the Uncompressed PCM 5.1 was better on the low end(more bass). Anybody want to tell me what they think about this review? Does anyone own the movies I have listed at the beginning of this thread for comparisons? Once again this thread is about what do you HEAR!

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post #18 of 37 Old 08-30-2007, 01:11 AM
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I think a 'review' like that, done sighted, is pretty dubious.


if you do such comparisons sighted, then what you HEAR may be very much what you SEE and what you EXPECT --consciously or not.
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post #19 of 37 Old 08-30-2007, 01:40 AM
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If you look at your reflection in a square mirror Vs. a rectangular one does the image that is reflected still look the same?
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post #20 of 37 Old 08-30-2007, 07:15 AM
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Quote:
Originally Posted by ekb View Post

Here's a thought. Decoded TrueHD is bit for bit identical to PCM 5.1 if the decoder makes no errors and has no drop-outs. Is there any chance that there is some level of error rate? I assume that low levels of errors would be covered by perfect error correction. But higher error rates and drop-outs would need to be concealed by interpolation. Hence there might be some level of bit discrepancy between the two and possibly audible under careful listening conditions.

Ed

One aspect of lossless compression is there can be no errors, let alone interpolation. If there was, it would no longer be lossless. If you zipped up a word document and then unzipped it to find some letters are replaced because of errors, would you consider that acceptable? Hardly, and the same applies here. The checksum either matches or doesn't, and if it doesn't you need to stop and try again.

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post #21 of 37 Old 08-30-2007, 07:22 AM
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Quote:
Originally Posted by kemiza View Post

A very reputable person in the audio/video world told me you can hear a difference between the two soundtracks. He played Ghost Rider on a PS3 & a Yamaha 1.2 receiver, using Klipsch reference speakers. He said the sound was identical on the high end but the Uncompressed PCM 5.1 was better on the low end(more bass). Anybody want to tell me what they think about this review? Does anyone own the movies I have listed at the beginning of this thread for comparisons? Once again this thread is about what do you HEAR!

Again, this could be due to encoding choices made by the studio and not reflective of the two formats. I'm not criticizing your quest for opinions here, but the question in the title is a dead horse. You would need to focus on particular titles rather than the generalizing the two formats.

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post #22 of 37 Old 08-30-2007, 10:52 AM
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Quote:
Originally Posted by littlesaint View Post

One aspect of lossless compression is there can be no errors, let alone interpolation. If there was, it would no longer be lossless. If you zipped up a word document and then unzipped it to find some letters are replaced because of errors, would you consider that acceptable? Hardly, and the same applies here. The checksum either matches or doesn't, and if it doesn't you need to stop and try again.

I remember when CDs first came out and Audio magazine tapped into the error correcting chip and monitored how often correction was been performed and how often error concealment was being performed. And they were taking place at a realatively high rate. So I wouldn't say "there can be no errors". I think one difference between decoding and unzipping is that the decoding must be accomplished in real time.

Ed
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post #23 of 37 Old 08-30-2007, 11:10 AM - Thread Starter
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I would like to thank everyone for participating in this thread. Some of you are intelligent and very well informed on the subject. Does anyone own ANY of the movies listed on this thread for feedback? Could that person please step forward with a post on what you hear.

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post #24 of 37 Old 08-30-2007, 11:26 AM
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post #25 of 37 Old 08-30-2007, 11:52 AM
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Quote:
Originally Posted by ekb View Post

I remember when CDs first came out and Audio magazine tapped into the error correcting chip and monitored how often correction was been performed and how often error concealment was being performed. And they were taking place at a realatively high rate. So I wouldn't say "there can be no errors". I think one difference between decoding and unzipping is that the decoding must be accomplished in real time.

Ed

That's error correction for reading the PCM off of the physical media. When decoding lossless compression there can be no (and usually are no) errors. Here's a quote from Dolby Labs on MLP compression:


“The CRC system used for PCM is the wrapping used to protect the data delivered on the disc itself. There is no error correction global to the process from the point of the encoder input to the decoder output. For example, PCM data is often altered, usually without (the engineer’s ) knowledge, as it passes from one place to another. Low level bits may be truncated or the data may be resampled, even if the sample rate is not being changed…MLP data is self–checked such that it can verify that the final PCM being decoded from the MLP unpacker is identical with the data that was input to the MLP encoder. If the data has undergone any subtle changes along the way, the output stops. In other words, if the MLP decoder is outputting PCM, then it can be assumed to be the same you gave it. This assumption cannot be guaranteed for other PCM pathways..." "MLP Machinations"

The article is in reference to DVD-A, but it is the same compression used in TrueHD.

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post #26 of 37 Old 08-30-2007, 08:56 PM
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Quote:
Originally Posted by littlesaint View Post

That's error correction for reading the PCM off of the physical media.

I assume that it's possible and even likely that errors will be made reading the compressed TrueHD off the physical medium. What happens then if there is no error correcting?
Quote:


When decoding lossless compression there can be no (and usually are no) errors.

Isn't this a contradiction?

Ed
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post #27 of 37 Old 08-31-2007, 08:23 AM
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Quote:
Originally Posted by ekb View Post

I assume that it's possible and even likely that errors will be made reading the compressed TrueHD off the physical medium. What happens then if there is no error correcting?

Ed

I'm sure there is error detection and correction reading the physical media just as there is with CDs, but that has nothing to do with error detection during the decoding of the TrueHD.

Error detection does occur during the decoding process (parity bits, checksums, etc), but there is no correction. If an error is detected, the decoding stops. So, errors can happen (again very rare), but decoding will not continue if they do.

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post #28 of 37 Old 09-02-2007, 07:15 PM
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Quote:
Originally Posted by kemiza View Post

I would like to thank everyone for participating in this thread. Some of you are intelligent and very well informed on the subject. Does anyone own ANY of the movies listed on this thread for feedback? Could that person please step forward with a post on what you hear.

I compared the two in "300" BD.
I thought the subharmonics were a tad louder on the pcm.
Other than that they're nearly identical.

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post #29 of 37 Old 09-02-2007, 09:48 PM
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I thought the subharmonics were a tad louder on the pcm.

Wouldn't subharmonic be completely absent audio? How can one absent signal be louder than another?

Ed
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post #30 of 37 Old 09-03-2007, 04:12 AM
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Quote:
Originally Posted by ekb View Post

Wouldn't subharmonic be completely absent audio? How can one absent signal be louder than another?

Ed

sorry, did not actually think of what i wrote.
i meant low bass information between 20 to 40 hz.

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