Standard DVD can use three audio formats, these being two channel PCM (Pulse Code Modulation) mainly used for music/concert based disks and two lossy compression formats, DD AC-3 (Dolby Digital) and DTS (Digital Theater System).
Lossy compression means that in compressing the signal material that is not deemed important such as frequencies higher than human hearing abilities, or masked by other sounds is removed and lost forever.
So the uncompressed output will not be identical to the original source.
Lossless compression doesn't remove anything, just compresses the source resulting in a bit for bit duplicate of the original digital source when it's uncompressed and is therefore indentical to the source.
DD can provide up to six (5.1) channels and has a data transfer rate (bit rate) of 192 kb/s for stereo, and either 384 kb/s or more commonly 448 kb/s for 5.1 material.
Likewise DTS can also do 5.1 but has a higher bit rate of 768 kb/s and sometimes 1.5 Mb/s.
Just because the the bit rate numbers are higher for DTS doesn't mean that it's better than DD because DD uses more efficient compression so 448 kb/s DD is about the same quality as 768 kb/s DTS.
The new High Definition DVD formats, Blu-ray and HD DVD not only have a far superior picture when compared to DVD but much better sound as well.
This is because there's a lot more room on the disk so less compression, or even none is needed so bit rates can be much higher.
Sadly whilst we only had three audio formats to worry about with DVD there's now a total of seven available for Blu-ray and HD DVD.
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Movies (dialog, music and sound effects) are recorded, mixed, edited and everything else in PCM.
This multi channel PCM master track can be put directly onto Blu-ray and HD DVD disks with up to a maximum of eight channels (7.1) and in either 16 bit or 24bit format and at 48khz or 96khz sampling rates.
All the other audio formats use this PCM master track and compress it, using lossy or lossless algorithms so that it takes less room on the disk.
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| Summary of available formats |
| Format [1] | Compression | Channels | Bit Rate |
Blu-ray | HD DVD | Coaxial/Optical | HDMI 1.3 |
| PCM | None | 7.1 | 18.9 Mb/s | Mandatory | Mandatory | Yes (2 channel) | Yes |
DTS-HD
Master Audio | Lossless | 7.1 | 24.5 Mb/s Blu-Ray [2], [3]
18.0 Mb/s HD DVD [2], [3] | Optional | Optional | No | Yes |
| Dolby TrueHD | Lossless | 7.1 | 18.0 Mb/s [2] | Optional | Mandatory | No | Yes |
DTS-HD
High Resolution | Lossy | 7.1 | 6.0 Mb/s [3] | Optional | Optional | No | Yes |
Dolby Digital Plus
(DD+) | Lossy | 7.1 | 1.7 Mb/s [4]
1.5 or 3.0 Mb/s [5] | Optional | Mandatory | No | Yes |
| DTS | Lossy | 5.1 | 1.5 Mb/s | Mandatory | Mandatory | Yes | Yes |
| DD AC-3 | Lossy | 5.1 | 640 kb/s | Mandatory | Mandatory | Yes | Yes |
[1] Listed in order of data transfer rates and maximum channels available.
[2] Maximum but typical rates are in the order of 5-10 Mb/s.
[3] Includes a lossy 1.5 Mb/s core.
[4] For Blu-ray coded as an extension of a 640 kb/s DD AC-3 core.
[5] HD DVD with typically 1.5Mb/s being used.
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| Current usage of formats (Updated July 2008) |
| Format | Blu-Ray [1] | HD DVD [2] |
| PCM | 33.9% |  | 0.7% |  |
| DTS-HD Master Audio | 19.5% | | 0.2% | |
| Dolby TrueHD | 14.88% | | 23.6% | |
| DTS-HD High Resolution | 2.5% | | 2.8% | |
| Dolby Digital Plus (DD+) | 0.0% | | 82.3% | |
| DTS | 2.0% | | 5.5% | |
| DD AC-3 | 26.2% | | - [3] | - [3] |
[1] Source: www.blu-raystats.com/Stats/Stats.php
[2] Source: www.hddvdstats.com
[3] Not used for HD DVD because DD+ is instead.
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| Which format is the best? |
There's no easy or in fact correct answer to this question but PCM and the two lossless formats, DTS-HD Master Audio and Dolby TrueHD should be superior to all the lossless formats.
Having said that it's the general consensus amoungst people that know about these things that 3.0 Mb/s DD+ is audibly as good as any of the lossless formats or PCM but sadly most DD+ soundtracks use the lower 1.5 Mb/s bitrate.
Blu-ray with it's greater storage capacity tends to favour PCM and the lossless formats with 69% of all disks using these, 35% of which use PCM.
Lossless formats on HD DVD only account for 24% of all disks and the overwhelming choice for HD DVD is DD+ with 82% of all disks using it.
Not that you have to worry about choosing between the various audio formats or even have the option of doing so because apart from a very few disks, PCM, DTS-HD Master Audio and Dolby TrueHD are mutually exclusive on most disks.
So you'll usually get just one of these and one or both of the lossy formats such as DD or DTS.
And even though PCM, DTS-HD Master Audio and Dolby TrueHD should all produce identical bit for bit copies of the original PCM master and therefore should all sound identical to each other, there are other factors that come into it if you're trying to work out which one is best (in your system).
All players of both formats must provide support for PCM, that is decode it internally to analog or output it as PCM for processing by an AVR (Audio Video Receiver).
For a HDMI connection this is multi-channel but for Coaxial/Optical connections it's two channel (stereo) only.
Just about all AVRs (even old ones) will accept PCM input.
Support for Dolby TrueHD is pretty good as it's a mandatory format for HD DVD and whilst only an optional format for Blu-ray most Blu-ray players will either decode it internally to analog or output it as PCM or native bitstream for processing by the AVR.
Support for DTS-HD Master Audio is improving with several players offering similar processing choices as with Dolby TrueHD.
All players seem to support DD+ and of course they all handle DD and DTS and for current player audio specs this BD Player Audio Support Comparison on AVS forum is a good place to look.
Looking at the above table "Summary of available formats" you'll note that none of the new audio formats are available unless you're using a HDMI connection.
The exception being PCM which can at least output a two channel (stereo) signal via a coaxial or optical lead which could then be processed by any AVR to at least provide simulated surround effects by using Dolby Pro-Logic or similar decoding.
So if your AVR only has optical or coaxial digital inputs you'll be limited to two channel PCM or the legacy DD or DTS tracks on the disk.
But if this is the case then it's not all bad news as DD is 640 kb/s (only 448 kb/s on DVD) and DTS is 1.5 Mb/s (usually 768 kb/s on DVD) so you're still getting better quality audio than with DVD.
| Analog support and connections |
Most players available now include analog outputs for up to six channels (5.1) and some even support 7.1 that can be used to connect the player to any older AVR that doesn't support HDMI.
Or if you just prefer to use analog connections to your AVR as most good ones now include multi-channel analog inputs.
All players will decode PCM, DD and DTS to analog and more and more are offering internal decoding to analog of DD+, Dolby TrueHD and DTS-HD Master Audio.
| Analog, bitstream or PCM? |
Depending on how good your player is, specifically it's DACs and assuming it can internally decode the various formats there's a lot to be said for letting the player do all the decoding and sending the audio to your AVR as multi-channel analog.
Some people with audiophile leanings claim this gives superior audio quality by avoiding the use of digital connections and conversions (other than the first one).
However it should be noted that if any post processing is done in the AVR, such as speaker sizing, distance, bass management and any "soundfields" then it will no doubt be done in the digital domain and therefore the first thing the AVR will do to an analog input is convert it to digital.
So this in effect adds additional layers of analog to digital and digital to analog processing.
Or you can still let the player do all the decoding but instead of converting to analog send it to your AVR via a HDMI connection as PCM.
The advantage of this is that you're already (or should be) using HDMI for the video so it saves using six (or perhaps even eight) additional analog leads.
The third method, providing your player supports it is to simply output the audio from the player as a bitstream (raw digital data stream) and use the decoders (if present) in the AVR.
This is popular with some people because they get to see the audio format displayed on the front panel of their AVR's rather than just a generic "Multi-channel".
Apart from that and depending on the quality of your player and/or AVR there may, or may not be any advantages to using this method.
Supporting the use of this last method is a suggestion that HDMI is prone to jitter (although evidently the lastest spec HDMI 1.3a fixes this issue) and that this isn't good when sending PCM whereas it isn't a problem when you send bitstream via HDMI.
The jury is still out on this one though as the effects of possible excessive jitter on a multi-channel movie soundtrack may not be that noticeable.
And to add further confussion to this topic is a suggestion by at least one person that works for Dolby Labs and had a fair bit to do with the development of TrueHD is that it's better to decode in the player as it takes some of the processing load of the AVR.
For the record I bitstream from my XE-1 (because that's what it does) and I send PCM from my PS3 (because that's what it does) and they both sound fine.
| And that leaves us where exactly? |
Well hopefully not any more confused than when you started reading this.
There are not only lots of possible audio formats on Blu-ray and HD DVD but lots of options in getting them from the disk to our speakers.
And whilst you can get all stressed about not being able to use what you consider to be the "best" audio format or decode it in the way you would like to, even the lowest quality format offered, 640 kb/s DD AC3 is still an improvement on what we get on most SD DVDs.
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