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Compressed vs Uncompressed Lossless (1 Viewer)

Wes K

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Specifically looking at the Harry Potter blurays, the first 5 films have a 5.1 LPCM track at a fixed 5.8Mbps, but the last 3 films have either a TrueHD or DTS-HD MA track.

Having just finished the 5th film and starting the 6th, I've been astonished by the increase in surround and LFE activity even though the TrueHD track varies at an average of 2-3Mbps. (According to my bluray player outputting bitstream)

My question is, does the compressed TrueHD decode with more info than a LPCM could have at 5.8Mbps?

Is the about TrueHD file size measured before it's decoded/expanded?
 

gadgtfreek

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I was always under the impression LPCM vs TrueHD/MasterHD were identical. Ive always bitstreamed TrueHD and MasterHD to an AVR, and the difference is obvious to me vs Dolby Digital 5.1 tracks, but not sure on LPCM.
 

Wes K

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I was always under the impression LPCM vs TrueHD/MasterHD were identical. Ive always bitstreamed TrueHD and MasterHD to an AVR, and the difference is obvious to me vs Dolby Digital 5.1 tracks, but not sure on LPCM.
I've read everywhere that they're all "bit by bit identical to the master" but it makes no sense to me that the sound design is drastically better when a compressed losses codec is introduced.
 

gadgtfreek

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I can say one thing, the few LPCM only movies I have, I never felt they were as good as TrueHD/MasterHD, but ya never know if that is just the way it was done.

Same thing with LPCM concerts.
 

Wes K

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I can say one thing, the few LPCM only movies I have, I never felt they were as good as TrueHD/MasterHD, but ya never know if that is just the way it was done.

Same thing with LPCM concerts.
It might just be how they did the sound design like you said, because the first 3 Pirates of the Caribbean movies are LPCM and they are fantastic.
 

Dave Upton

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LPCM is not completely lossless. The way LPCM works is that the lossless audio track is transcoded from DTS-HD or Dolby TrueHD/Atmos to PCM before leaving the player. This data is extremely close to the source, but isn't "bit perfect". This results in a sometimes minimal, sometimes substantially reduced amount of information for your AVR or processor. When you enable "bitstreaming" for audio on your player, you are sending the actual DTS/Dolby file directly to the AVR without unpacking it first, letting the much better DACs (Digital to Analog Converters) and chips in your processor/AVR do their job, which usually results in improved sound quality.

EDIT: PCM (also known as pulse code modulation)is an uncompressed format - it's basically the same as a wav or wave file on your computer. That means that even though it can handle 27mbps of info, that's not as much as you think with 8 or more channels and no compression.

DTS-HD:MA and Dolby TrueHD/Atmos are compressed, so despite their lower bitrates than LPCM, they carry more data. This is because they are significantly more efficient at storing audio data. The result is that the bit depth and sampling rate of the audio in these containers is often higher than LPCM would be due to bandwidth limitations. A TrueHD track could be 24-bit 192KHz, while LPCM is only 24bit/48KHz.

Bitstreamed lossless tracks can sometimes equate to 30-40 or more mbps or LPCM bandwidth, so the bitstreamed audio encode may be superior, and will often sound better and have more low level information. That's the difference you are hearing.
 
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Wes K

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LPCM is not completely lossless. The way LPCM works is that the lossless audio track is transcoded from DTS-HD or Dolby TrueHD/Atmos to PCM before leaving the player. This data is extremely close to the source, but isn't "bit perfect". This results in a sometimes minimal, sometimes substantially reduced amount of information for your AVR or processor. When you enable "bitstreaming" for audio on your player, you are sending the actual DTS/Dolby file directly to the AVR without unpacking it first, letting the much better DACs (Digital to Analog Converters) and chips in your processor/AVR do their job, which usually results in improved sound quality.
I think you misunderstood my question. Some Harry Potter blurays have an LPCM surround mix at 5.8 mbps that is sent straight to the receiver because it needs no decoding. The later Harry potter movies have truehd or dtshd ma which are sent to the receiver and decoded. (I know the decoding in bluray players is worse than a receivers).
 

Dave Upton

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I think you misunderstood my question. Some Harry Potter blurays have an LPCM surround mix at 5.8 mbps that is sent straight to the receiver because it needs no decoding. The later Harry potter movies have truehd or dtshd ma which are sent to the receiver and decoded. (I know the decoding in bluray players is worse than a receivers).
I edited to address this. Conventional lossless codecs like FLAC save 30-40% bandwidth, based on what we know the results are similar with DTS:HD and TrueHD, so that's why a lower bitrate compressed DTS-HD/TrueHD track can sound better than a higher bitrate uncompressed LPCM track.
 

Wes K

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I edited to address this. Conventional lossless codecs like FLAC save 30-40% bandwidth, based on what we know the results are similar with DTS:HD and TrueHD, so that's why a lower bitrate compressed DTS-HD/TrueHD track can sound better than a higher bitrate uncompressed LPCM track.
So a 2-3mbps compressed codec when decoded can contain more information than a 5.8mbps uncompressed? I'm just trying to understand if using a compressed codec equates to more surround/sound activity as a whole.
 

Dave Upton

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So a 2-3mbps compressed codec when decoded can contain more information than a 5.8mbps uncompressed? I'm just trying to understand if using a compressed codec equates to more surround/sound activity as a whole.
The answer is that it can, but not always. The person who does the encoding has many knobs they can touch which will result in a differing output file size.

This could be a combination of better mixing, more data (due to compression) or other factors. The important thing to remember is that the lossless compressed codes (Dolby TrueHD/Atmos and DTS:HD/X) have a higher theoretical max sound quality than LPCM due to compression.
 

Mark-P

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Just a thought, on the LPCM titles are you absolutely sure your receiver is receiving a 5.1 pcm stream and not a downmixed 2.0 stream?
 

Josh Steinberg

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I don't have a great memory for how these films sounded in their different configurations, but I wonder if sound design has just gotten more involved over the course of the series. Is it possible that the mixes from the latter films simply feature more surround and LFE effects because they were mixed that way? It wouldn't surprise me to discover that the sound design of a film originally released in 2001 was less expansive than one from a 2011 release.
 

Wes K

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I don't have a great memory for how these films sounded in their different configurations, but I wonder if sound design has just gotten more involved over the course of the series. Is it possible that the mixes from the latter films simply feature more surround and LFE effects because they were mixed that way? It wouldn't surprise me to discover that the sound design of a film originally released in 2001 was less expansive than one from a 2011 release.
You are probably right, and because it isn't that old and hasn't received a remix. Maybe they redid the sound design for the 5.1 dts-hd ma track on the Blu-ray that comes in the UHD release.
 

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