What's wrong with TrueHD?!?

[DaViD Boulet]

Just a general tutorial for anyone confused:

there are currently two "paradigms" of digital music reproduction:

1. PCM (pulse code modulated)
2. DSD (direct stream digital).

Most consumer and professional media works in PCM. Sony's SACD is one of the few consumer technologies that uses DSD.

The digital audio on CD, DVD, DVD-A, even your iPod and MP3 player is all build on the backbone of PCM.

Any technologies that use compression (lossy or lossless) because of space limitations start with a PCM signal before compression... and end up with a PCM signal *after* decompression. Only a PCM signal can be run through a d/a converter (leaving out Sony's SACD/DSD for the moment).

The difference between lossy and lossless compression is that with lossless you get back the *same* PCM signal after decompression that you started with. In theory, no loss of quality because of this. Lossy compression can't recapture the full quality of the original PCM, and so it's compromised by design.

[TauRus]

Originally Posted by werewuf

Okay here is the word: I just spoke to the local South San Francisco Bay Pioneer rep on the phone. Dolby THD and DTS HDMA are proprietary...

No one is claiming they are not proprietary.

Originally Posted by werewuf

What you get by decoding with their chips are their mixes, and it's different than when it's PCM. In his words "Then it wouldn't be Dolby or DTS" ...

Now, this is where it get weird - what do you mean by that? "Their mixes"??? There should be only one mix of tracks on the dis - the one designed by a sound engineer. If what you were saying was true, then that would mean that on a DolbyTHD the tracks are -remixed in a different way, which is obviously bogus. Again, there was a lot of misunderstanding going on in your discussion with the DTS rep.

Originally Posted by werewuf

... he said keep trying to get your point across because the mix is their product not just the bitstream" PCM, Dolby THD and DTS HDMA are different from each other.

You see, what he is implying through your interpretation, is that DTS is rearranging the audio signal, which is wrong. Their "product" is an intermediary audio package, a ".zip file" so to speak. Let's take a look in a very simplified way at what happens with the audio information:
1) Audio Authoring stage: Sound engineer mixes various audio tracks to a certain way. The tracks at that point are in PCM.
2) Audio Conversion stage: in order to fit the original PCM tracks onto a disc, the tracks are converted to DolbyTHD or DTS-HDMA or any other flavor. At that stage the files are in proprietary Dolby or DTS formats.
3) Disc Authoring stage: Multiple tracks are recorded on a disc, sometimes including PCM tracks, DolbyTHD and others.
4) Disc Playback stage: Now, here we have some variables. For simplicity let's just review the DolbyTHD scenarios, the same will apply to DTS-HDMA playback options.
4A - your player does not have any DolbyTHD decoding - therefore if you select a DolbyTHD track, your player only extracts core Dolby audio signal skipping all HD info, basically it decodes the DolbyTHD as a slightly improved Dolby EX track. The output is still a PCM track, but it is lacking the high definition information, therefore is not as rich as the master PCM, has less dynamic range, less sound stage, etc. So, in this case the decoding is lossy.
4B - your player has a DolbyTHD decoder, but it cannot output the DolbyTHD via bitstream - in this case once the DolbyTHD track is selected, the audio material is losslessly decoded back to PCM, theoretically must be identical to the original PCM mix, otherwise the term "lossless" should not even apply.
4C - your player has a DolbyTHD decoder, and it can either decode the DolbyTHD track internally (then scenario 4B takes place); or it can bitstream the original DolbyTHD track to the outside device (receiver / processor) where all the decoding takes place. So, in case you opt to decode the DolbyTHD track internally, then the output is PCM, if you elect to decode it externally then the output is bitstream.
5 - Receiver / Processor stage - Again we have two scenarios:
5A - the DolbyTHD track was decoded by your player internally and therefore the audio information was sent out as PCM. In this case receiver accepts PCM signal, applies some optional processing (bass management for example), then sends it off to the amp section. The story ends here.
5B - the DolbyTHD track was bitstreamed out of the player. Your receiver takes the bitstream, decodes it (if it has the capability to do so) to PCM, then possibly applies some additional processing like bass management and then send it to the amp.
This is of course a simple digram but should be pretty accurate as far the PCM to Dolby to PCM conversions.

Originally Posted by werewuf

... PCM, Dolby THD and DTS HDMA are different from each other...

Yes they are different things: PCM is an audio format, DTS and Dolby are audio compression technologies.

Originally Posted by werewuf

... The difference I heard from THD converted to PCM or DD with my old player was noticeable. When THD was played as DD (on some soundtracks) it did not have the dynamic range of full THD...

Again, as far as I know, THD or HDMA do not "improve" the audio compared to PCM. The differences in audio that you heard can be explained by a number of things: how your receiver is handling different signal types / inputs, post-processing, or possibly by the fact that the master PCM files and the PCM track on the disc are different, i.e. the master PCM had higher resolution than the PCM track that ended up on the disc.

I am happy to hear any corrections and comments if my statements were inaccurate. But this is what I believe to be the way things work with these new audio compression technologies.

[gandley]

no they dont improve the audio, but they save space and bitrate to get the same level of performence. If you read the MLP document i linked to it tells you exactly how its all done.

[gandley]

for 2 chaneel downmixing of multi channel audio

7 TWO CHANNEL DOWNMIX
It is often useful to provide a means for accessing highresolution
multichannel audio streams on 2-channel
playback devices. In an application such as DVD-Audio,
the content provider can place separate multi- and twochannel
streams on the disc. However to do this requires
separate mix, mastering and authoring processes and
uses disc capacity.
In cases where only one multichannel stream is
available, then there are very few options at replay – one
is to use either a fixed or guided downmix. However, to
create such a downmix it is first necessary to decode the
full multichannel signal; this contravenes the desirable
principle that decoder complexity should decrease with
functionality.
7.1 Performing mix-down in the lossless encoder
MLP provides an elegant and unique solution. The
encoder combines lossless matrixing with the use of two
substreams in such a way as to optimally encode both
the Lt/Rt downmix and the multichannel version.
This method is shown in Figure 17.
Downmix instructions are used to determine some
coefficients for the lossless matrices. The matrices then
perform a rotation such that the two channels on
substream 0 decode to the desired stereo mix and
combine with substream 1 to provide full multichannel.
Because the 2-channel downmix is a linear combination
of the multichannel mix, then strictly, no new
information has been added. In the example shown in
Figure 17 there are still only six independent channels in
the encoded stream. So, theoretically, the addition of the
2-channel version should require only a modest increase
in overall data rate (typically 1 bit per sample, e.g.
96kbit/s at 96kHz). Figure 18 shows an example where a
downmix is added to the 6-channel segment from Figure
12.
The advantages of this method are considerable:
§ The quality of the mix-down is guaranteed. The
producer can listen to it at the encoding stage and
the lossless method delivers it bit-accurate to the
end user.
§ A 2-channel-only playback device does not need to
decode the multichannel stream and then perform
mix-down. Instead, the lossless decoder only need
decode substream 0.
§ A more complex decoder may access both the 2-
channel and multi-channel versions losslessly.
§ The downmix coefficients do not have to be
constant for a whole track, but can be varied under
artistic control.

[bluseminole]

Originally Posted by Blu-Ray Buckeye

From Greg's reveiw at digitalbits:

The audio is no less disappointing. Encoded with both Dolby TrueHD and linear PCM tracks, Spider-Man 3 on Blu-ray is a breathtaking aural experience.

May I just point out that this is just horrible writing. He says the audio is "no less disappointing" then follows by saying it's "a breathtaking aural experience". Do people even proofread any more? When you say "no less disappointing" it means that whatever you were just talking about was disappointing and so in this.

When you say "no less disappointing" it means that whatever you were just talking about was disappointing and so is this.

[quetzalcoatl]

Where yes in theory these should all sound the same. I for one know they donot. I really think it is a simple as the fact of sending a bitstream of TrueHD or PCM is the fact that as a bitstream it is all being done by the same componet, the receiver. Now I think we all know sometimes things donot play well together. I just did a test with Surfs Up and the TrueHD track had a warmer feel than the PCM. And this should not happen in theory.
And with a sound meter they might be the same. But lets faces the facts that our ears are not sound meters. And audio is the most subjective thing in HT.

[werewuf]

Originally Posted by gandley

Im not getting that at all.

PCM is not very effiecent, so Dolby and DTS have come up with a way to store PCM with more compression to save space. i guess you have heard of MLP lossless audio which we now know as true HD

Meridian Lossless packaging is a lossless coding system for high quality linear PCM, thats right its just a repackaging system for linear PCM

This has gone on long enough that I just got of the phone with a Pioneer tech in LA. His words: PCM, THD, and HDMA are separate, proprietary encoding that differ from each other. With THD and the BDP-94 player, it is played through as PCM or DD. When it is, it is no longer THD. You are not getting the full encoding of Dolby's mix. The only way to get THD's full picture is with THD decoding, if it is read any way you are not getting it. If True HD as played through as PCM were exactly the same there would be no reason to have both versions of the soundtrack on the same disc. PCM and THD are not just two ways to open a file. Anytime there are more than one format of soundtrack you are going to have different mixes and different quality. That is what they are there for, also to facilitate the fact that the consumer has different generations of equipment that may or may not be able to play whatever formats are available.

[DaViD Boulet]

werewuf,

you're on the verge of getting it but still not quite there. He's talking about gear that cannot "fully decode" the TrueHD. Yes... if you have a player that can't FULLY decode the TrueHD, then it does one of two things:

1. passes the "lossy DD core" to your recevier.
2. converts the "lossy core" to 5.1 PCM and passes that to your receiver over HDMI (1.1 or higher).
3. convert to PCM from the lossy core and then dowmix to 2.0 for passing over old-fashioned digital.

Either way, you're not unzipping the lossless TrueHD file... just the lossy part.

If you have a player that CAN fully decode the TrueHD, then it can do one of two things:

1. pass this lossless file over HDMI 1.3 to a receiver that can decode TrueHD.
2. Extract the lossless file to PCM and pass in 5.1 over HDMI 1.1 or higher in decoded form (same quality).
3. Downmix the 5.1 to 2.0 and pass as stereo PCM over old-fashioned SPDIF.


You're talking about the first part. We're talking about this second part.
Making more sense?

True HD as played through as PCM were exactly the same there would be no reason to have both versions of the soundtrack on the same disc.

You are CORRECT! The reason that Sony is providing both is sort of a temporary experiement. It was to give them a chance to get used to mastering in TrueHD but they wanted to keep PCM going when possible for a while since not all BD players can fully decode TrueHD just yet. Paidgeek also said it was to offer a rare chance for guys like us to compare the two versions that, in theory, were supposed to be identical in playback. You can see where that has led!

But yes, if everything is working "right", then you'd never really have both on the same disc... just one or the other since they both represent the same PCM file (the TrueHD just packing it more efficiently).

[gandley]

They are different as far as packing technology goes but they all achieve the same goal. much like taking a movie's master and either encoding with Mpeg2 or AVC or VC-1.

so its simple, PCM gets coverted to MLP or in this case trueHD or DTS MA. (which in turn saves space and possible bit rate)

but to unzip the converted PCM file you need a trueHD decoder or a DTS MA decoder (so they can get the license fee). a PCM file converted to trueHD can not be converted by a DTS MA decoder, so they are different beasts that originate from the original raw PCM Source

Linear PCM can best be decribed as the raw signal again like a movie master. Blu ray has the capacity and bandwidth to pass linear PCM. However its not exactly efficent or intelligent but its high quality.

So thus came MLP which Dolby turned into TrueHD, which efficently and intelligently converts linear PCM to save capacity and peak bandwidth. DTS have there own technology to do the same thing.


I dunno, linear PCM needs a huge suitcase but trueHD and DTS MA can transport the same cloths with no creases in a briefcase.

[Brain Sturgeon]

Just to clarify, from how I understand how TrueHD works, there is no "Lossy DD Core" that it is built around. All of the TrueHD packets are lossless, with the first packet containing 2 channel lossless mix which is downmixed twice from the original 7.1 mix (7.1 to 5.1, then 5.1 to 2), the first extension packet containing the additional 3.1 channels to add to the first packet to produce a 5.1 lossless soundtrack (this is derived from the 7.1 to 5.1 downmix), and finally the second extension packet containing the final 2 lossless channels of the 7.1 mix. Therefore, the Dolby decoder should be doing all the work to produce either a 2, 5.1, or 7.1 lossless mix depending on how your player is set to decode the format. You cannot get a 5.1 DD soundtrack out of a TrueHD soundtrack no matter how you set up your player-- you would just be listening to the standard separate DD soundtrack that is mandatory on Blu-ray.

DTS-HD HR and MA are built around a lossy core (1.5 Mbps DTS), which is one of the major distinctions between these two formats.

[DaViD Boulet]

Brian,

right. Because TrueHD is built on MLP, it's not an extension from a Dolby Digital "core" at all, unlike Dolby Plus and DTS-HD/MA which build on a basic "core" plus extension data to acheive the higher quality.

HOWEVER,

on Blu-ray Disc, the way that the additional DD base-stream is required, it *acts* like a "core". For instnace, it doesn't need to be directly-accessible via a menu or listed on the package... just a TrueHD is all that needs to be "presented" to the user. If they can't decode it... then the standard Dolby stream is put in its place. But if you toggle through the audio options you won't find a trueHD and separate regular DD stream... only one stream, the trueHD, is "presented" to the user (the substitution is covert).

I use the term "core" in a venacular sense, the same way that 16x9 DVDs are not truly anamorphic, but that term gets used to describe the effective result to the end-user.

[Brain Sturgeon]

DaViD-- thanks for the info; I wasn't aware of the default to DD state that BD has when TrueHD is selected but can't be decoded/passed (e.g. if you try to bitstream TrueHD via TOSLINK on a PS3).

This whole issue begs the question-- assuming that the TrueHD and the PCM soundtracks are identical word lengths and sampling rates (and I understand that this is not always the case-- Spider man is an example of this with 16/48 PCM and 24/48 THD) then why include both same language soundtracks on the same BD? Doesn't this argue that the encoder knew that they were not the same? It would be like including the original file and a .zip file in an online download. Of course, the whole issue of DN clouds this whole thing since we know that DN definitely changes the soundtrack.

Anyways, just thinking out loud.

[DaViD Boulet]

Brian,

Paidgeek has already explained (in other threads) that Sony is only duplicating lossless redundantly like this (trueHD and PCM on the same disc) temporarily while they learn the ropes of mastering TrueHD and as a courtesy to consumers who still may not have full TrueHD decoding-capable hardware. He said they also thought it would offer a rare chance to give consumers the abiltiy to compare directly for themselves. Clearly we have... and clearly it's lead to some confusing impressions (ie, that the two "duplicate" lossless tracks don't sound the same).

In the future, Sony will drop PCM from TrueHD titles.

[AlexBC]

Originally Posted by LembasBread

So on The Fifth Element, audible differences w/ the TrueHD being superior are a little suspect. Paidgeek has stated that the TrueHD and LPCM tracks for that title are compressed from the same 16-bit master.

It has been stablished before that The Fifth Element's DTHD track is @ 48/20 upconverted from 48/16

Originally Posted by quetzalcoatl

I just did a test with Surfs Up and the TrueHD track had a warmer feel than the PCM. And this should not happen in theory.

From what I read Surf's UP DTHD track is 48/24 while the PCM is 48/16 just like Spider 3.

Maybe paidgeek can confirm this

[quetzalcoatl]

Well I have not watched the whole movie yet on my Blu-ray but I did about 15 mins then did the same 15 mins again changing the audio. And I must say I cannot disagree more with what was said.
Now granted I am listening to both of the uncompressed tracks in 5.1. And theTrueHD track has a much warmer feel. And sounds from off the screen are clearer.

My opinion is there is nothing wrong with the TrueHD track it is the better of the two avail.

[LembasBread]

Originally Posted by AlexBC

It has been stablished before that The Fifth Element's DTHD track is @ 48/20 upconverted from 48/16

Yes, but it's still from a 16-bit master recording. Unlike video, audio can't be "upconverted" - you can't add audio information that wasn't recorded to begin with. So while it's in a 20/48 TrueHD stream, it should still sound like a 16-bit track.

[shamus]

Just found this thread...
I noticed the PCM sounded a bit better myself. I was really surprised to learn the PCM track is 48/16 and TRU 48/24. If anything should have sounded better it should of been TRU...

Im using the Panny with everything set to PCM and sent VIA HDMI to a 7.1 system.(Denon receiver, RBH speakers)
I only compared the opening credits and will try the Mary Jane scene later.
To be fair... I didn't level match, and the difference was very minor and could only be heard "on the fly".

My amateur oversimplified opinion is anytime you try to compress and uncompress sound.... things can go wrong. I am very excited to hear DTS masters as it appears to be a real power horse!(and is hinted by Richard from R&B films to be superior to TruHD)

I do find it humorous that while the HD-DVD crew argues whether there is a difference between lossy and lossless, we compare the differences between just lossless formats!

[DaViD Boulet]

Yes, but it's still from a 16-bit master recording. Unlike video, audio can't be "upconverted" - you can't add audio information that wasn't recorded to begin with. So while it's in a 20/48 TrueHD stream, it should still sound like a 16-bit track.

Actually you *can* upconvert audio... in EXACTLY the same way you upconvert video. You interpolate new datapoints (or interpolate additional resolution with existing datapoints) via whatever algorithm you choose. You can simply "fill in between the dots" which is what the oversampling filter in your average CD player does. You can try to do sine-wave prediction via sophisticated algorithms that try to correct for 16-bit quantization error. In any case, you *can* interpolate and convert 16 to 20 bits.

This doesn't necessarily mean you've improved the sound. You might have worsened it... just like a bad scaler is worse than no scaler.

You can also just "pad with zeros" to increase word length.

All Dolby decoders output a 24-bit word regardless of the original waveform's resolution. Most do this by padding. But any additional DSP happens in the 24 bit realm and would result in "data" in the 8 additional LSBs.

Well I have not watched the whole movie yet on my Blu-ray but I did about 15 mins then did the same 15 mins again changing the audio. And I must say I cannot disagree more with what was said.
Now granted I am listening to both of the uncompressed tracks in 5.1. And theTrueHD track has a much warmer feel. And sounds from off the screen are clearer.

My opinion is there is nothing wrong with the TrueHD track it is the better of the two avail.

Can you share more? Did you notice a level-difference between the two tracks with the TrueHD being softer? Or were they they same perceived level?

I'm actually *hoping* that the problem lies with the way my PS3 is handling/downmixing compared to PCM and not something with the TrueHD stream itself.

[DaViD Boulet]

I do find it humorous that while the HD-DVD crew argues whether there is a difference between lossy and lossless, we compare the differences between just lossless formats!

I had thought the same thing.

[MacDaddyOJack]

I'm sure that the companies have to pay royalties to Dolby when they use the TrueHD compression, so my question is this: Why would you use the TrueHD compression if you have ample space for PCM on the Bluray disk?? It sounds like there are dialogue normalization issues on teh new TrueHD tracks, so why not just stick with PCM for those times when space is not an issue??