Original Dolby Digital track or downmix True HD? - AVS Forum
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post #1 of 17 Old 10-02-2008, 02:35 AM - Thread Starter
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The Blade Runner blu-ray has Dolby True HD and Dolby Digital tracks.

My sound system only copes with Dolby Digital and DTS.

Is is better to play the original Dolby Digital track off the disc or downmix the True HD to DTS (or Dolby Digital) in software?
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post #2 of 17 Old 10-02-2008, 06:47 AM - Thread Starter
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To clarify:
My sound system is connected by optical cable and is old (only capable of Dolby Digital and DTS not any HD formats).

The software blu-ray player can either:
1. output the Dolby Digital 5.1 track off the disc through the optical cable
2. take the Dolby True HD track and trancode it to either DTS 5.1 or Dolby Digital 5.1 and output through the optical cable

Presumably transcoding Dolby True HD to Dolby Digital is pointless, but if DTS has higher bitrate, then maybe Dolby True HD->DTS 5.1 is better than original Dolby Digital track?
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post #3 of 17 Old 10-02-2008, 07:01 AM
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Quote:
Originally Posted by mcarans View Post

To clarify:
My sound system is connected by optical cable and is old (only capable of Dolby Digital and DTS not any HD formats).

The software blu-ray player can either:
1. output the Dolby Digital 5.1 track off the disc through the optical cable
2. take the Dolby True HD track and trancode it to either DTS 5.1 or Dolby Digital 5.1 and output through the optical cable

Presumably transcoding Dolby True HD to Dolby Digital is pointless, but if DTS has higher bitrate, then maybe Dolby True HD->DTS 5.1 is better than original Dolby Digital track?

What player do you have that can transcode TrueHD to either DD or DTS? Many Toshiba HD DVD players had that capability, but I am not aware of any BD players that transcode. I believe a BD player will play a companion DD track if you select the TrueHD track for output over optical.

As to whether legacy DD or DTS is better, bitrates aren't all that meaningful. DD is more efficient. If you hear a difference, use the one you prefer when you have such a choice.
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post #4 of 17 Old 10-02-2008, 07:08 AM - Thread Starter
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I'm playing from a PC - I think any blu-ray player software available has this functionality eg. WinDVD, PowerDVD.

I was thinking from a technical perspective - is the transcoding process from Dolby True HD to DTS something that would degrade the sound?
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post #5 of 17 Old 10-02-2008, 10:55 AM
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Quote:
Originally Posted by mcarans View Post

I'm playing from a PC - I think any blu-ray player software available has this functionality eg. WinDVD, PowerDVD.

I was thinking from a technical perspective - is the transcoding process from Dolby True HD to DTS something that would degrade the sound?

Yes, of course.

TrueHD is a lossless encode where the output is identical to the original soundtrack. DTS and DD are lossy compression codecs. Some of the data they remove during encoding is not restored in decoding. There are lengthy (endless) debates about which lossy format produces better sound. Try them both and see if one sounds better to you.

Bitrate comparisons between the formats are not meaningful, as noted in my previous post. But, you will want the DTS transcode to be 1.5mbps and the DD one to be 640kbps. Those are the highest rates supported by the two formats.
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post #6 of 17 Old 10-03-2008, 12:11 PM - Thread Starter
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Thanks for your reply.

Beyond the degradation from the fact that DTS and Dolby Digital are lossy formats, is there any further degradation due to the process of converting one format to another?
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post #7 of 17 Old 10-03-2008, 01:02 PM
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Quote:
Originally Posted by mcarans View Post

Beyond the degradation from the fact that DTS and Dolby Digital are lossy formats, is there any further degradation due to the process of converting one format to another?

I'm not sure what you are asking, here. What "further" degradation might there be? Or, I guess a better question for us to ask is "what is the nature of the degradation that occurs upon downmixing?". Whatever it may be, it is the degradation that occurs. There are not different degradations. There is only degradation. (Does that make sense?)

But I think that your original question has not really been answered. That being, and I quote from your initial post, "Is is better to play the original Dolby Digital track off the disc or downmix the True HD to DTS (or Dolby Digital) in software?". I don't know the answer, but my inclination would be to think that utilizing the specifically mixed tracks (if they are indeed present) would be better than relying upon the software downmix. Excepting the difference in the surround channels between the 8 channel and 6 channel mix, I guess the crux of this question is "might there be other differences between the hirez tracks and the DD/DTS tracks besides the resolution?". I would suspect that this is the only difference. However, I suppose that if they are specifically mixed, perhaps even by different engineers, that this may not be the case.

The other question that sort of arose was "if the disc has a specific DD track, but no specific DTS track, but you can downmix the TrueHD to DTS, which is best?". This answer is more complicated. If the downmix to DTS is at a higher bitrate than the specifically mixed DD track, and that is the only difference, then, as BIslander hinted, it may be best to use the DTS downmix. But the answer may depend upon the downmixing algorithm that is used by your software as well as the quality of your software downmix. In other words, and sorry to pose another question, "excepting the resolution difference that may be present between the TrueHD to DTS downmix versus the specifically mixed DD track, might there be other differences between the two choices that would warrant using the specifically mixed DD track instead?". And I do not think the answer is so easy. Again, to pose yet another question, "excepting the difference between an 8 channel and 6 channel mix, if there really is some other mixing difference between the TrueHD track and the specifically authored DD (or DTS) track that is still present upon downmixing the TrueHD track, whether it be to DD or DTS, would it be better to utilize the downmix?" Again, even if there is some sort of mixing difference between the TrueHD track and the specifically authored DD (or DTS) track, I would expect it to be minor. It may be that the DD/DTS tracks that are included are simply downmixes of the original TrueHD track in the first place. In which case how the TrueHD track was downmmixed upon engineering versus how your software would downmix the TrueHD soundtrack might come into play.

In your specific example, I am tempted to say to try it all 3 ways; TrueHD downmixed to DTS versus TrueHD downmixed to DD versus the specifically authored DD track. But I hesitate, as I think it would be really hard to come to some decision that one could absolutely attribute to being solely due to those differences.

In other words, don't waste your time worrying about it and just enjoy the movie.

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post #8 of 17 Old 10-03-2008, 01:19 PM
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Quote:
Originally Posted by sivadselim View Post

I'm not sure what you are asking, here. What "further" degradation might there be? Or, I guess a better question for us to ask is "what is the nature of the degradation that occurs upon downmixing?". Whatever it may be, it is the degradation that occurs. There are not different degradations. There is only degradation. (Does that make sense?)

But I think that your original question has not really been answered. That being, "Is is better to play the original Dolby Digital track off the disc or downmix the True HD to DTS (or Dolby Digital) in software?". I don't know the answer, but my inclination would be to think that utilizing the specifically mixed tracks (if they are indeed present) would be better than relying upon the software downmix. Excepting the difference between 8 channels and 6, I guess the crux of this question is whether or not the only difference between the hirez tracks and the DD/DTS tracks is the resolution.

Doesn't it depend on whether there is any difference between the legacy DD track on the disc and the one created by the software transcode? What bitrates are used in both approaches? In most cases, the DD track on a BD will be encoded at 640kbps. Does the OP's software transcode at the same rate? Are all DD encoders/transcoders the same? I have no idea about that myself. The lossy process means some data is removed. If the two encoders remove different data, then the outputs will likely sound different.

This strikes me as a rather esoteric discussion among people (me, at least) who don't understand much about how these processes work. Besides, we're talking about lossy outputs here. How much different can they be? I suggest the OP try a few tests comparing the DD track on the disc with the transcoded TrueHD output and see if it makes a difference.
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post #9 of 17 Old 10-03-2008, 01:39 PM
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Quote:
Originally Posted by BIslander View Post

Doesn't it depend on whether there is any difference between the legacy DD track on the disc and the one created by the software transcode? What bitrates are used in both approaches? In most cases, the DD track on a BD will be encoded at 640kbps. Does the OP's software transcode at the same rate? Are all DD encoders/transcoders the same? I have no idea about that myself. The lossy process means some data is removed. If the two encoders remove different data, then the outputs will likely sound different.

This strikes me as a rather esoteric discussion among people (me, at least) who don't understand much about how these processes work. Besides, we're talking about lossy outputs here. How much different can they be? I suggest the OP try a few tests comparing the DD track on the disc with the transcoded TrueHD output and see if it makes a difference.

Yes, I added quite a bit to my post. Sorry for being so fickle. And esoteric.

As I pointed out, excepting the higher resolution and the difference in the 8 versus 6 channel mix, whether the TrueHD and specifically authored DD (or DTS) mixes are otherwise identical or not, I think it is possible that the software downmix of the TrueHD track could be different from the exact original intent of the TrueHD track. In which case, whether it is identical to the TrueHD track's mix or not, it may be best to use the specifically authored DD (or DTS) track. In other words, if it were me, I might be inclined to use the track that was specifically authored instead of a downmix. At least, then, you know that you are hearing exactly what an engineer intended and not what your software is spitting out.

But I agree with you 100%. This is some major hairsplitting which, in the end, is probably irrelevant. If mcarans finds he can hear some difference between the choices that he "thinks" sounds "better", then he should just use that and be done with it and enjoy the movie. But (and I hate to add this) he may find that his preference is specific to this particular disc, for whatever reason(s), and that that preference may be different with another disc.


LOL! OY! Why am I back here at AVS posting again?!?!?!?!

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post #10 of 17 Old 10-11-2008, 07:05 AM - Thread Starter
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Thanks to both of you for your detailed responses.

I've noticed since getting the Bladerunner blu-ray that another possibility on the disc is uncompressed PCM (Pirates of Caribbean At World's End). I've also now had a DTS-HD disc (Die Hard 4) that made it simple as it outputted fine as standard DTS. I think that DTS were pretty smart in going down this route as I'm inclined to say that the sound quality of this was better than Dolby Digital tracks on the other 2 discs.

I think you guys are right in suggesting that the track on the disc is likely in most cases to be better than software downmixing as it's likely that the studios will do a better job than a cheap transcoder.

Thanks alot.
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post #11 of 17 Old 12-08-2008, 12:15 AM
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Quote:
Originally Posted by sivadselim View Post


In your specific example, I am tempted to say to try it all 3 ways; TrueHD downmixed to DTS versus TrueHD downmixed to DD versus the specifically authored DD track. But I hesitate, as I think it would be really hard to come to some decision that one could absolutely attribute to being solely due to those differences.

Sorry for bringing this thread up again, looks like I'm going to be in a situation where I will soon have a blu-ray player (Samsung BD-P2500) connected to my old Onkyo receiver using 5.1 analog out. For the sake of this discussion, my BD-P2500 allows you to turn off L & R surr back channels and can process 24bit/192kHz. I will be receiving the blu-ray player sometime this week to do some real world testing...

My questions are:
1) Isn't it true that Dolby TrueHD is a Dolby thing, and so why are you guys talking about TrueHD being downmixed to dts??? It's mentioned like that in a few of the conversations here in this thread.

2) I was under the impression that you CANNOT select the original(core) DD or dts audio track when your blu-ray player is TrueHD or dts-HD compatible. From what I have read, it seems the original DD or dts tracks are "hidden" and not selectable from the blu-ray audio menus. Is this correct?

3) My other "real" concern is 24bit/192kHz or 24b/96kHz issues. If even possible that you can pass the original(core) DD or dts via TOSLINK optical cable to an old receiver that cannot do 24/192 or 24/96 processing, then isn't the audio quality degraded say compared to, the blu-ray player downmixing the DD or dts (either the uncompressed or the DD/dts(core)) since the blu-ray player is doing the processing in 24/192 or 24/96 ?

I thought the point in this original discussion was to figure out the downmixed quality vs. the original(core) DD/dts being passed thru to the receiver.

My apologies if some areas of my questions might sound like I am the poor fella who is confused.
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post #12 of 17 Old 12-08-2008, 12:19 AM
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Quote:
Originally Posted by mcarans View Post

To clarify:
My sound system is connected by optical cable and is old (only capable of Dolby Digital and DTS not any HD formats).

The software blu-ray player can either:
1. output the Dolby Digital 5.1 track off the disc through the optical cable
2. take the Dolby True HD track and trancode it to either DTS 5.1 or Dolby Digital 5.1 and output through the optical cable

Presumably transcoding Dolby True HD to Dolby Digital is pointless, but if DTS has higher bitrate, then maybe Dolby True HD->DTS 5.1 is better than original Dolby Digital track?

What receiver or amp do you have?

Does it have discrete 5.1 analog INPUTS ? And, does your receiver or amp have 24bit/192kHz or 24bit/96kHz audio processing?
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post #13 of 17 Old 12-08-2008, 07:59 AM
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Quote:
Originally Posted by work4mike View Post

1) Isn't it true that Dolby TrueHD is a Dolby thing, and so why are you guys talking about TrueHD being downmixed to dts??? It's mentioned like that in a few of the conversations here in this thread.

Transcoded, not downmixed. The original track gets decoded and re-encoded using a different codec. HD DVD did that routinely. BD does not use that approach. The OP in this thread was also talking about transcoding. Downmixing means reducing the number of channels - re-mixing a 7.1 track to 5.1, for example.

Quote:


2) I was under the impression that you CANNOT select the original(core) DD or dts audio track when your blu-ray player is TrueHD or dts-HD compatible. From what I have read, it seems the original DD or dts tracks are "hidden" and not selectable from the blu-ray audio menus. Is this correct?

DTS uses a core + extension structure. The core is DTS 5.1 and can be processed by any DTS decoder. The extension contains the other parts needed for things such as lossless dts-MA. When you select a dts-MA track, the player will use the portions that work for your player or interface to a receiver.

DD uses a separate, usually hidden, DD track. But, the process is the same. The player outputs the version that works for your player/receiver interface.

Quote:


3) My other "real" concern is 24bit/192kHz or 24b/96kHz issues. If even possible that you can pass the original(core) DD or dts via TOSLINK optical cable to an old receiver that cannot do 24/192 or 24/96 processing, then isn't the audio quality degraded say compared to, the blu-ray player downmixing the DD or dts (either the uncompressed or the DD/dts(core)) since the blu-ray player is doing the processing in 24/192 or 24/96 ?

There aren't any 192 kHz encodes. As for 96 kHz, most players have a setting to down-res PCM from 96 to 48 for receivers that can't handle the higher sampling rate. If your receiver can handle 96 kHz, then you won't have a problem. There are only a handful of 96 kHz discs to begin with. Almost all Blus are 48 kHz.
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post #14 of 17 Old 12-08-2008, 03:31 PM
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Quote:
Originally Posted by BIslander View Post


There aren't any 192 kHz encodes. As for 96 kHz, most players have a setting to down-res PCM from 96 to 48 for receivers that can't handle the higher sampling rate. If your receiver can handle 96 kHz, then you won't have a problem. There are only a handful of 96 kHz discs to begin with. Almost all Blus are 48 kHz.

Thanks for the great clarification. I am still learning as much as I can, but miss some of the details here and there...

If I may ask for your advice and opinions: Which way to connect is better? My old receiver (DD/DTS capable) can accept 5.1 analog inputs by connecting only 5.1 analog outs OR use the TOSLINK optical.

My Onkyo receiver has one unique feature, for DTS 24/96 material the audio is processed at 96kHz. ASSUMING this means "bitstream" as optical input to it, correct or no?

On the Samsung blu-ray, I can use EITHER the 5.1 (manual says to leave L&R surr back unconnected for any 5.1 receiver connections) or you can choose to send via TOSLINK optical out. (2 TOSLINK modes available in my case~ see below info from the player manual)

I do not understand what is going on in both these options since it seems that all the decoding is already done on the blu-ray anyways.

The Blu-ray TOSLINK out has 3 modes, but only 2 for me since I don't do HDMI:

1)PCM mode:
Decodes Primary, Secondary and Effect audio streams together into PCM audio.

Pros: You can enjoy Primary, Secondary and Effect audio together. You can also enjoy Dolby TrueHD sound even if your receiver cannot decode Dolby
TrueHD.

Cons: You cannot hear DTS-HD Master Audio sound with this setting
even if you have an HDMI 1.3 receiver which has DTS-HD Master Audio decoding capability. (Note: Samsung will add this as a feature in f/w upgrade)

Recommended choice if you have an HDMI 1.1 or HDMI 1.2 receiver which cannot decode DTS-HD Master Audio. Also recommended if you are
using an optical cable for audio and your receiver cannot decode
Dolby Digital or DTS.


2) Bitstream(Re-encode) mode:
Decodes Primary, Secondary and Effect audio streams together into PCM audio, then re-encodes the PCM audio into DTS bitstream.

Pros: You can enjoy Primary, Secondary and Effect audio together.

Cons: Audio quality may be lower than PCM or Bitstream (Audiophile) setups.

Recommended choice if you don’t have an HDMI supported receiver, but have a receiver with an Optical input that can decode DTS.
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post #15 of 17 Old 12-08-2008, 04:16 PM
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Quote:
Originally Posted by work4mike View Post

If I may ask for your advice and opinions: Which way to connect is better? My old receiver (DD/DTS capable) can accept 5.1 analog inputs by connecting only 5.1 analog outs OR use the TOSLINK optical.

Analog gets you lossless from a player that can do the decoding. Toslink is limited to legacy DD and DTS. However, the legacy formats are encoded at high bit rates on BD because of Blu's larger disc size and they rival the quality of lossless. Only you can decide whether one is better than the other.

Quote:


My Onkyo receiver has one unique feature, for DTS 24/96 material the audio is processed at 96kHz. ASSUMING this means "bitstream" as optical input to it, correct or no?

Most DTS decoders on BD ignore the 96/24 flag. So, the only way to get 96/24 processing is by bitstreaming it to your receiver for decoding. Most AVR decoders will process the 96/24 extension.

Quote:


On the Samsung blu-ray, I can use EITHER the 5.1 (manual says to leave L&R surr back unconnected for any 5.1 receiver connections) or you can choose to send via TOSLINK optical out. (2 TOSLINK modes available in my case~ see below info from the player manual)

I do not understand what is going on in both these options since it seems that all the decoding is already done on the blu-ray anyways.

See my comment above. If the player does the decoding, you can get lossless. But, of course, the player has to have the needed decoders. The Samsung doesn't do dts-MA yet.

If you bitstream over optical, you get the older DD and DTS codecs instead. in that case the tracks are not decoded by the player. Bitstream means the encoded track is sent to a processor for decoding.

Quote:


The Blu-ray TOSLINK out has 3 modes, but only 2 for me since I don't do HDMI:
1)PCM mode:
Decodes Primary, Secondary and Effect audio streams together into PCM audio.

This is worthless for you. Optical can only carry two channels of PCM. All you get is stereo, not 5.1 surround. PCM is worthwhile if you are using HDMI.

Quote:


2) Bitstream(Re-encode) mode:
Decodes Primary, Secondary and Effect audio streams together into PCM audio, then re-encodes the PCM audio into DTS bitstream.

This is the one to use.
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post #16 of 17 Old 12-08-2008, 06:11 PM
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Quote:
Originally Posted by BIslander View Post

Analog gets you lossless from a player that can do the decoding. Toslink is limited to legacy DD and DTS. However, the legacy formats are encoded at high bit rates on BD because of Blu's larger disc size and they rival the quality of lossless. Only you can decide whether one is better than the other.

Most DTS decoders on BD ignore the 96/24 flag. So, the only way to get 96/24 processing is by bitstreaming it to your receiver for decoding. Most AVR decoders will process the 96/24 extension.


.

BIslander, you have been truly awesome!!.

Thank you so much for the explanations and the clarity on this subject!
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post #17 of 17 Old 12-08-2008, 06:36 PM
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Glad I was able to help. Home Theater audio can be confusing at times.
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