Dolby TrueHD and DTS HD demystified
By Ben Drawbaugh 
posted April 26th 2007 3:26PM
posted April 26th 2007 3:26PM
There seems to be some confusion about the next generation HD movie discs and audio CODECs. Unlike the video CODECs used on both formats, the new audio CODECs are lossless which simply means without loss, or identical to the original. The three lossless CODECs supported by both formats are LPCM, Dolby TrueHD and DTS HD MA. At this point the question should be, if they are lossless than what is the difference? The difference for the most part is the number of bits. Both Dolby TrueHD and DTS HD use far less bits than LPCM, this leaves more space on the disc for other features. Of course audio is always more complicated than just CODECs, there is also the sample rate to consider and 
For DTS I think you are referring to DTS-HD Master Audio not DTS-HD High resolution audio. This is just clarification since DTS-HD gets confusing.
Good point, I added the MA to the end of the first mention of DTS HD.
LPCM is not being used at higher than 48kHz sampling rate because of the datarate/storage that would require.
Dolby TrueHD definitely supports higher sampling rates than 48kHz.
DTS-HD MA and Dolby TrueHD can support the same Bit depth and sampling rate as LPCM, i.e. up to 196kHz and 24bit.
Talk of 24/96 and 24/196 is all academic, though. Aside from studio music recordings, nothing is recorded at that fidelity. In the future, we might see some music releases with 24/96 DTS-HD MA or 24/96 TrueHD, but that's about it.
All modern movies are mixed at 24/48.
LPCM is not a codec. It's Uncompressed Linear PCM just like CD Audio. DTS-HD MA and TrueHD are lossless compression schemes aka codecs. Get your facts right. DTS-HD (without the "MA") is a very high bitrate, yet LOSSY codec. DTS-HD Master Audio (or "MA" as most of us call it) is lossless.
The primary complaint of LPCM is that it hasn't been used to deliver the full quality of master audio tracks, due to space and bandwidth concerns.
The DTS-HD MA and TrueHD lossless compression formats can deliver full 24/48 master quality audio in about the same bandwidth and space as LPCM at lower 16/48 fidelity.
There's some debate whether LPCM at downconverted 16/48 fidelity is really an improvement over 24/48 DTS @ 1.5Mbps (lossy). In some situations, it may be an improvement, and it others, it may be worse. Providing the full 24/48 audio master does away with such questions, becuase nothing is more faithful to the master than the master itself. Unfortunately, 24/48 LPCM requires more bandwidth than is available with most titles on BD25, and even some BD50 titles with MPEG-2. That's where DTS-HD MA and TrueHD come in; those codecs can losslessly pack the 24/48 LPCM stream, saving significant bandwidth and space.
yes , but how great would a 96/24 Blue Man Group concert be? :)
Also erroneous is the reference in the post to "16/24" sound.
ok....heres one thing that i dont understand, maybe someone can clue me in here. The main difference between the DTS and Dobly Digital formats of years past was the amount of compression that was basically put on the audio mix itself. That was, if my thinking is correct, the primary difference between the two formats. Now that we have the storage capabilities to do completely lossless audio, with no compression...why is there still a DTS-HD and DOBLY-HD. if my reason is faulted please someone let me know...
"Now that we have the storage capabilities to do completely lossless audio, with no compression...why is there still a DTS-HD and DOBLY-HD. if my reason is faulted please someone let me know..."
The link provided by engadget explains it.
But simply said, there isn't space to provide "completely lossless audio, with no compression" on most disks. Completely lossless audio for all modern films is 24-bit, 48kHz. But there isn't space for that on most disks used today. So what do studios do? They "downres" the 24-bit, 48kHz LPCM master track to 16-bit, 48kHz LPCM. It's still uncompressed audio, but it's no longer lossless compared to the master. It's lossy.
TrueHD and DTS-HD MA are lossless compression codecs -- like zip files -- which are used to "zip" the 24-bit, 48kHz LPCM so it can fit on every disk. That eliminates the need to "downres" the audio to lower / lossy resolution.
"They "downres" the 24-bit, 48kHz LPCM master track to 16-bit, 48kHz LPCM. It's still uncompressed audio, but it's no longer lossless compared to the master. It's lossy."
False. You cannot call 16-bit PCM lossy, and call 24-bit lossless. Any sampled audio is lossy by this defintion because even 24-bit sampling introduces some error from the original analog source. Down res-ing or lowering the bit-depth adds more error, but dithering can help keep it close to sounding like the higher bit-depth version.
No PCM is considered lossy ever. Lossy and lossless are terms that are only given to compression types. Lossy compression actually removes frequencies that are too hard for the human ear to even notice missing. Lossless keeps all frequencies but still manages to reduce the filesize.
The zip file is a good analogy. Asking why use TrueHD & DTS-MA over LPCM is like asking why software is zipped before you download it. When it is uncompressed nothing is lost it is bit to bit identical to the original. If the original sound track was 011101010101010101010101011111101011101011010110 then after decompressing TrueHD you will have exactly 011101010101010101010101011111101011101011010110.
LPCM offers nothing over TrueHD except it takes about about 2x the space. Either your player or receiver needs to support TrueHD and DTS-MA though. The good thing about HD DVD is that every single player MUST support TrueHD decoding. In 10 years when there is a $40 Apex HD DVD player it will support TrueHD. With BD TrueHD is optional and if neither your player or receiver support it then you can't listen to it.
Engadget one point of your article is 100% wrong. All three HD audios (LPCM, TrueHD, DTS HD-MA) support the same resolution. On both HD formats all 3 go up to 192/24 @ 7.1 channels. LPCM provides no higher benefit. Actually TrueHD supports up to 192/24 with 24 channels but both Bluray & HD DVD "limit" it to 8 channels (7.1)
Sorry for the confusion, I must of misunderstood the link. I crossed out that part.
Thanks
So Im still confused and stupid about this. It has nothing to do with the quality of the audio, just the space?
Why do they still record in the analog domain. With todays technology cant everything be done in the digital domain, hence without the need for A/D and D/A conversion.
"False. You cannot call 16-bit PCM lossy, and call 24-bit lossless. Any sampled audio is lossy by this defintion because even 24-bit sampling introduces some error from the original analog source."
By definition, lossy refers to a recording that is different from the original. Of course, all audio is lossy -- at some level -- compared to the original performance when A/D was done. What is the point of even mentioning that? The reality is that you never hear -- nor are you meant to hear -- the original performance. It is mixed and enhanced many times over for optimal performance in a multichannel environment. In many cases, what you get on the film's audio master may be very little like the original recording -- by INTENTION.
Most modern film mixing is done in the digital domain. Many film mixers never see an analog source in 2007. The are mixing recordings acquired and distributed on digital tape. Once mixed, the multichannel 24/48 master track -- already dithered from higher resolution sources to eliminate quantization noise -- is archived on D5-HD format along with the video.
Lossy compression refers a method of compression by which the compressed version is no longer identical to the soruce. Being uncompressed, PCM @ 16/48 is certainly not lossy compression, but it is lossy relative to the digital master stored in multichannel 24/48 on D5-HD. That digital master is straight from the studio mixer -- it is the highest quality track recording available for the theatrical release. All other encodings are derived from that track.
To the above, I'll just add that 16-bit doesn't automatically equate to lossy.
It is only in the past five years or so that it became standard industry practice to master and store theatrical multichannel mixes at 24/48. A decade ago, it was common practice to use 16/48. On those older titles, 16/48 is as good as it gets.
However, if you see a newer movie released on Blu-ray or HD-DVD with 16/48 track, you aren't getting the full quality of the multichannel digital master.
Is it really necessary to capitalize CODEC in 2007? I know it's short for compressor-decompressor -- but it's not an acronym.
It's a bit like the obnoxious PLAYSTATION3.