HD-DVD audio nonsense

[richard plumb]

OK, can someone please help me get my head around the way audio works on HD-DVD, and how it compares to bluray.

It seems like if a disc has a Dolby TrueHD soundtrack recorded in 'advanced' mode, then this will not be passed down the HDMI, or the optical out.

Instead, the player decodes it into 7.1PCM, then re-encodes it to DTS and sends that down the optical cable.(this apparantly is player by player specific, some may recode to DD). It can also send this down the 7.1 analogue outs if the player has them.

this is apparantly so that it can 'mix' the audio in realtime, but I'm at a loss to understand why it would need to do that. :lease:

[sbowler]

Welcome to the "confused club" its another selling point, giving the consumer the idea that its a new vastly improved medium over old DD/DTS will we really hear a difference?

[DanielTS]

It seems like if a disc has a Dolby TrueHD soundtrack recorded in 'advanced' mode, then this will not be passed down the HDMI, or the optical out.

In advanced mode, every soundtrack (DD, DD+, Dolby TrueHD, DTS, DTS-HD) is decoded (and mixed) in PCM, and the PCM flow will be passed down the HDMI.

In HD disc players, the audio will be handled in the same fashion. Soundtracks decoded from the disc, as well as audio elements streamed or downloaded from an Internet connection or generated internally in the player, will be decoded in the player as digital PCM signals. PCM is the format players use to perform all internal audio processing operations, including mixing. In the mixing stage, streaming commentary, button sounds, and other non-disc-audio will be mixed with the native 5.1 or 7.1 soundtrack from the disc. The result will be the complete audio presentation as intended by the content maker.
http://www.dolby.com/images/consumer/technology/trueHD/fig1.jpg
http://www.dolby.com/consumer/technology/trueHD/AVRs/trueHD_avrs_1.html

Standard Content & Advanced Content (aka iHD) :
http://www.watch.impress.co.jp/av/docs/20051006/dvd09.jpg

Here is the one minute tutorial on HD DVD menu system/interactivity. There are two modes:

1. Standard. This your current DVD menu. If authored this way, the player should just send out the bitstreams as defined on disc.

2. Advanced. This is "iHD" subystem which all the US titles use (Japanese titles use #1). iHD allows for multiple audio streams/Picture-in-Picture. Each track can have its own encoding, sampling rate, etc. The player then is responsible to decode all and mix them. Now, if it does not compress them back, you have no way of sending multi-channel audio out of the S/PDIF connection as it is not fast enough for uncompressed (multi-channel). So Toshiba has chosen to use a DTS Encoder at maximum rate to preserve all the fidelity they can.

Hope this makes more sense now.

Amir
http://www.avsforum.com/avs-vb/showthread.php?p=7498142&&#post7498142

[richard plumb]

they do all that fuss so that they can mix in *button sounds*!?

and whats that about director commentaries? Surely that'd just be a separate track with a lower volume background audio mix? They can do that on itsy bitsy DVDs, surely they can do that with humungous HD-DVDs?

It seems completely arse about face to me

[ianh64]

and whats that about director commentaries? Surely that'd just be a separate track with a lower volume background audio mix? They can do that on itsy bitsy DVDs, surely they can do that with humungous HD-DVDs?

I think the point with mixing things inside the player is that, for example, with directors commentaries, you get full True HD soundtrack and the commentary is mixed with that. With DVD, I believe that the commentary is pre mixed with a lower quality soundtrack. In addition, there is the ability for the player to download low quality audio over the internet and this be mixed on the fly with high quality audio from the disc. I don't personally see much use in this at present but non the less, its a pretty powerful feature.

The biggest benefit that I see from this is that decoding the audio within the player frees up processing power downstream for the AV amp to concentrate on other things. This also means that an older AV amp does not need to know about the newer codecs - it only needs to beable to take a multi channel input, for example analogue or via PCM over HDMI 1.1 and the full benefit of True HD can still be experienced.

The latter is how some high end kit works - for example Meridian DVD players decode multi channel audio from DD, DTS and MLP (as used with DVD-A and is the core of Dolby True HD) and pass it via a 6 channel digital (at up to 96/24) link to their processors. The processor then upsamples the audio (at up to 192/24 for analogue) where jitter reduction, bass management, time alignment and room correction is applied. Without having to decode the signal within the processor, processing power is freed up to allow the processor to upsample. An alternative maybe that processing power if freed up that would allow cheaper processors to provide room correction.

[gorman]

I think that this is valid for current decoders which are unable to decode Dolby TrueHD and DTS*Whatever name their HD lossless format has*.

For a decoder capable of accepting those compression systems, I believe that you would get the audio stream non compressed straight through the HDMI cable. What you cannot get is the same stream through the SPDIF interface as, apparently, they're saying it doesn't provide enough bandwidth.

Personally, I have no intention of changing amp. Full bitrate DTS sounds really, really good. I'm not sure I could ABX it from the uncompressed sound.

[mr_yogi]

So if I understand this...

If you have an existing DD/DTS AV amp will the HD-DVD player "down mix" the Dolby TrueHD or DTS equivilent soundtrack on the HD-DVD disk to DD or DTS which can then be sent over standard optical/ Toslink(?) to the amp?

Or will the HD-DVD player output the analogue channels separatley which then feed the analouge inputs on the AV amp?:confused:

Thanks

[DanielTS]

So you have three choices for how to get the audio out of the A1/XA1. The way I view it is:

1) PCM over HDMI - Best (5.1 96/24)
2) Analog - Next Best (5.1 96/24 converted to analog)
3) SPDIF - Third Best (5.1 DTS)
if the disc is authored in Advanced Content mode.
http://www.avsforum.com/avs-vb/showthread.php?p=7498294&&#post7498294

And according to Amir from Microsoft all (actual) American HD DVD are authored in advanced mode.

[shaithis]

So if I understand this...

If you have an existing DD/DTS AV amp will the HD-DVD player "down mix" the Dolby TrueHD or DTS equivilent soundtrack on the HD-DVD disk to DD or DTS which can then be sent over standard optical/ Toslink(?) to the amp?

Or will the HD-DVD player output the analogue channels separatley which then feed the analouge inputs on the AV amp?:confused:

Thanks

I beleive you can do it either way.

I personally will be trying both but think I will stick with the analog connections for 7.1 as you can only get 5.1 with optical/TOSLink.

[ShornYeti]

This all sounds like a recipe for serious lip-sync issues, does HD have anything built in to the spec to deal with that?

[gandley]

if you use bitsream out via SPDIF dd+ etc will be forced to output DTS and not just plain DD with the new toshiba players. Mainly because DTS has higher bitrates.

as i posted elsewhere + more info on sound issues

The DTS issue is not really an issue at all, its just the way toshiba have implimented the sound decoders. If you use SPDIF out the sound will be converted to DTS even if you have selected DD+.

SSpears said

"All streams are decoded and if you are set to ouput bitsteam over SPDIF, it uses a real-time DTS encoder and re-compresses the audio"

More info here.
http://www.avsforum.com/avs-vb/showt...9&page=7&pp=30
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