[eric1514]

Hi all,


I purchased a couple of BD discs off the budget rack at Wallyworld (The Departed, Bram Stoker's Dracula), and both offer PCM 5.1 as an optional audio track along with DD 5.1.


I'm playing these discs with an LG BD370, set to "Primary Pass-Thru", connected via HDMI to a Yamaha RX-V465.


I understand, I think, that if I select DD 5.1, the Yamaha will decode the signal, decompress it and perform any nuances that Dolby applied along with any DSPs that I might have added. My questions are, what exactly is the receiver doing when it receives an uncompressed PCM signal and why would I even want to choose that option? Although I haven't listened to a lot of either soundtrack and doing an A-B comparison is next to impossible, my initial impression is that the DD track is much "fuller" than the PCM track.


TIA,

Eric

 

[sptrout]

PCM tracks are uncompressed digital recordings vs. the "lossy" or compressed DD 5.1. Remember that the "goal" of any lossy compression (DD or DTS, for example) is to provide audio that sounds as good as the original recording, which was PCM. Therefore, the 5.1 PCM tracks should sound better than any lossy format, but it is not uncommon for many not to be able to hear the difference. A statement to how good lossy DD or DTS can be.


BTW - - AVR decoders do not "decompress" lossy DD or DTS tracks, they just convert them from digital to analog. The only digital tracks that are uncompressed are DD's TrueHD & DTS-HD MA.

 

[bluesky636]



Quote:
Originally Posted by sptrout /forum/post/18166780


PCM tracks are uncompressed digital recordings vs. the "lossy" or compressed DD 5.1. Remember that the "goal" of any lossy compression (DD or DTS, for example) is to provide audio that sounds as good as the original recording, which was PCM. Therefore, the 5.1 PCM tracks should sound better than any lossy format, but it is not uncommon for many not to be able to hear the difference. A statement to how good lossy DD or DTS can be.


BTW - - AVR decoders do not "decompress" lossy DD or DTS tracks, they just convert them from digital to analog. The only digital tracks that are uncompressed are DD's TrueHD & DTS-HD MA.

First of all, a low bitrate lossy compression codec (legacy DD and DTS) when decoded will never sound as good as the original PCM soundtrack. Too much data has been thrown away. It is the comparison between high bitrate lossy compression codecs (DD Plus and DTS HD Hi-Resolution) and lossless compression codecs (DD True HD and DTS HD-MA) to the original PCM soudtrack where it is claimed a difference cannot be heard.


And, yeah, the decoder in an AVR most certainly does decompress lossy (low or high bitrate) DD/DTS codecs as well as the lossless codecs if the AVR is doing the decoding. The AVR will decompress and decode the codecs to PCM and then to analog. DD True HD and DTS HD-MA are also compressed, but use a lossless compression scheme.


If the BD player is doing the decoding than it will decompress and decode the lossy/lossless codecs to PCM and send the PCM stream to the AVR which will than convert the PCM stream to analog.


I suggest you do a little more research into lossy and lossless codecs to understand better how these things operate.

 

[sptrout]



Quote:
Originally Posted by bluesky636 /forum/post/18166945


First of all, a low bitrate lossy compression codec (legacy DD and DTS) when decoded will never sound as good as the original PCM soundtrack. Too much data has been thrown away. It is the comparison between high bitrate lossy compression codecs (DD Plus and DTS HD Hi-Resolution) and lossless compression codecs (DD True HD and DTS HD-MA) to the original PCM soudtrack where it is claimed a difference cannot be heard.


And, yeah, the decoder in an AVR most certainly does decompress lossy (low or high bitrate) DD/DTS codecs as well as the lossless codecs if the AVR is doing the decoding. The AVR will decompress and decode the codecs to PCM and then to analog. DD True HD and DTS HD-MA are also compressed, but use a lossless compression scheme.


If the BD player is doing the decoding than it will decompress and decode the lossy/lossless codecs to PCM and send the PCM stream to the AVR which will than convert the PCM stream to analog.


I suggest you do a little more research into lossy and lossless codecs to understand better how these things operate.

Actually, I understand very well how they work and have for many, many years. I think if you read what I said more closely you will see that we are saying nearly the same thing; you just a little better than my brief explanation.


1. I agree lossless tracks sounds to most to be far better than lossy, but as I am sure you have read, there have been blind A vs. B testing done where most listeners could not tell the difference. Not sure that I buy into that, but some so. Yet, you may be right that the testing was with higher bitrate CODECs, but I think it was with with standard DD & DTS. I do not have the time to find the link to the paper at this moment. In any case, many have written on this board that they cannot tell the difference.


2. An AVR cannot "decompress" a lossy track because that would mean that the AVR is recovering the bits that have been rejected when the audio is compressed in the first place, they do not. They just do the best they can to recreate what was eliminated. The DD & DTS tracks are "decoded" not "decompressed."


3. I agree that TrueHD & DTS-HD MA are lossless, compressed formats, and that the decoders on the user's side (either in the AVR or Blu-ray player) uncompress and then decode these tracks back to their original full PCM.


I think we are just mixing terms "decoded" & "compression" here more than anything. DD & DTS are "decoded" to PCM, and HD formats are "uncompressed" and then "decoded" to PCM. That is the way I keep things straight in my mind.


Here is the link to the article I was referring to: http://www.hemagazine.com/node/Dolby...compressed_PCM

 

[amicusterrae]



Quote:
Originally Posted by sptrout /forum/post/18167242


there have been blind A vs. B testing done where most listeners could not tell the difference. Not sure that I buy into that, but some so. Yet, you may be right that the testing was with higher bitrate CODECs, but I think it was with with standard DD & DTS. I do not have the time to find the link to the paper at this moment. In any case, many have written on this board that they cannot tell the difference.

just what I was about to say. This same debate occurred with SACD vs. redbook CDs. Some say they can hear a difference, but the ABX tests indicate otherwise. We're not talking about lossy MP3s. Now, I don't like the idea that "data has been thrown away." In the past disc storage limitations dictated this decision, but blu-ray has made it possible and economical to keep all the bits.


This probably isn't an intended benefit of the decision to include a MPCM track on a movie disc, but I like that with 5.1 MPCM, I could apply post processing in my receiver to matrix the back surround channels -- a la Logic 7 -- whereas I would be limited to Dolby IIx with the DD 5.1 track.

 

[bluesky636]



Quote:
Originally Posted by sptrout /forum/post/18167242


Actually, I understand very well how they work and have for many, many years. I think if you read what I said more closely you will see that we are saying nearly the same thing; you just a little better than my brief explanation.

That may be true.

Quote:
Originally Posted by sptrout /forum/post/18167242


1. I agree lossless tracks sounds to most to be far better than lossy, but as I am sure you have read, there have been blind A vs. B testing done where most listeners could not tell the difference. Not sure that I buy into that, but some so. Yet, you may be right that the testing was with higher bitrate CODECs, but I think it was with with standard DD & DTS. I do not have the time to find the link to the paper at this moment. In any case, many have written on this board that they cannot tell the difference.

Yes, the article you referenced is comparing the decoded results of lossless compression codecs (DD True HD/DTS HD-MA) to the decoded results of lossy compression codecs (legacy DD/DTS) on Blu-Ray. The fact that the medium is Blu-Ray is very important because the data rate of even the lossy legacy codecs is higher than that used on standard definition DVD.

Quote:
Originally Posted by sptrout /forum/post/18167242


2. An AVR cannot "decompress" a lossy track because that would mean that the AVR is recovering the bits that have been rejected when the audio is compressed in the first place, they do not. They just do the best they can to recreate what was eliminated. The DD & DTS tracks are "decoded" not "decompressed."

On this point I have to disagree. Quite simply, anytime you "compress" a file, you must go through a reciprocal "decompression" step to recover the data. That's a fact of digital life. The amount of data recovered during decompression is dependent on the type of compression used. "Lossy" compressed files, when decompressed will result in a file that is similar to but not identical to, the original file because data has been thrown away. Think JPEG compression. When you take a picture using JPEG compression, recreating the picture (decompressing the data) results in a picture pretty close to the original, but not quite. Some data has been lost. "Lossless" compressed files, when decompressed will result in an exact reproduction of the original file. Think TIFF compression. TIFF is lossless and when decompressed will result in an exact reproduction of the original picture.

Quote:
Originally Posted by sptrout /forum/post/18167242


3. I agree that TrueHD & DTS-HD MA are lossless, compressed formats, and that the decoders on the user's side (either in the AVR or Blu-ray player) uncompress and then decode these tracks back to their original full PCM.

See the above explanation. Any compression scheme, lossy or lossless, requires a reciprocal decompression scheme to recover the data.

Quote:
Originally Posted by sptrout /forum/post/18167242


I think we are just mixing terms "decoded" & "compression" here more than anything. DD & DTS are "decoded" to PCM, and HD formats are "uncompressed" and then "decoded" to PCM. That is the way I keep things straight in my mind.

Nope. As explained previously.

Quote:
Originally Posted by sptrout /forum/post/18167242


Here is the link to the article I was referring to: http://www.hemagazine.com/node/Dolby...compressed_PCM

There is an error in the article. The article says at the end: "The lossless, Dolby Digital Plus, and DTS-HD High Resolution compressed tracks were just a little more open and airy."


DD Plus and DTS HD High Res still use a lossy compression scheme. It is just "less" lossy than legacy DD and DTS.

 

[bluesky636]



Quote:
Originally Posted by amicusterrae /forum/post/18167460


This probably isn't an intended benefit of the decision to include a MPCM track on a movie disc, but I like that with 5.1 MPCM, I could apply post processing in my receiver to matrix the back surround channels -- a la Logic 7 -- whereas I would be limited to Dolby IIx with the DD 5.1 track.

DPL IIX works just fine to create back surround channels from 5.1 multichannel PCM. So does DTS Neo:6. I use DPL IIX all the time regardless of the audio format.

 

[sptrout]

OK blueske636 I am with you now. If the standard DD & DTS decoders did not uncompress the incoming digital stream to something as close to the original PCM as possible then everything would sound like Donald Duck. I must have had a "senior moment" (more like a senior 1/2 day

).


I like your comparison to JPEG pictures. I remember the very first time I started editing JPEG files, I worked a long time before going back and checking the resulting file sizes. I learned real quick that everytime I hit the "save" button my picture resolution got less and less. Nothing like learning the hard way.

 

[amicusterrae]



Quote:
Originally Posted by bluesky636 /forum/post/18168538


DPL IIX works just fine to create back surround channels from 5.1 multichannel PCM. So does DTS Neo:6. I use DPL IIX all the time regardless of the audio format.

I agree. I just prefer Logic 7

 

[bluesky636]



Quote:
Originally Posted by sptrout /forum/post/18169167


OK blueske636 I am with you now. If the standard DD & DTS decoders did not uncompress the incoming digital stream to something as close to the original PCM as possible then everything would sound like Donald Duck. I must have had a "senior moment" (more like a senior 1/2 day

).


I like your comparison to JPEG pictures. I remember the very first time I started editing JPEG files, I worked a long time before going back and checking the resulting file sizes. I learned real quick that everytime I hit the "save" button my picture resolution got less and less. Nothing like learning the hard way.

As they say: "A picture is worth a thousand words".

I use the JPEG/TIFF analogy a lot. People seem to be able to visualize that easier than what happens with a sound file. To complete the analogy, the original scene being photographed/PCM data stream I consider a "bitmap".

 

[bluesky636]



Quote:
Originally Posted by amicusterrae /forum/post/18169470


I agree. I just prefer Logic 7

I figured, but I have run across a few AVRs that don't let you apply DPL IIX to multichannel PCM due to DSP limitations. Wasn't sure if that was the case with you.