DTS-HD MA - WITHOUT! - a core

[deleted user]

Turns out you can encode DTS-HD MA - WITHOUT! - the core, saving valuable disk space. Just set the "Core Bit Rate" to "No Core".


This eliminates the two main problems I've always seen with DTS-HD MA, which made me never use it:

1. DTS-HD MA with a core is incredibly bloated and no good alternative to FLAC. However without the core it's only slightly bigger than FLAC and completely acceptable.

2. You never know whether your player is playing the true lossless audio or the core. For example, VLC will only play the core, but not tell you about it. So you think you're listening to the lossless audio, but you're not. However without a core, this is impossible. VLC will simply output only silence. MPC-HC will play it properly (yay!).


And if you really want a fallback for hardware that can't play DTS-HD MA, you can just include a format of your choice, like AC-3 or AAC. But of course the obvious goal is for people to listen to the lossless audio, so hey!

Now, my only question would be whether a coreless DTS-HD MA is properly compatible with receivers. Anyone care to test it out?

[bronan]

Ugh! Thanks for the info, didn't realize VLC had that limitation. This is why I just stick with PCM

[zoidberg]

I was under the impression that the core was an integral part of the format (and that of Dolby TrueHD) ie the core is first decoded and then the remaining data is added to reconstruct the original sound losslessly. Correct me if I'm wrong but surely removing this core would reduce the efficiency of the codec

[deleted user]

I was under the impression that the core was an integral part of the format (and that of Dolby TrueHD) ie the core is first decoded and then the remaining data is added to reconstruct the original sound losslessly. Correct me if I'm wrong but surely removing this core would reduce the efficiency of the codec

That's what I thought too, but the official DTS Suite allows you to encode without a core and the resulting file is much smaller. Seems that merely nobody ever tried it, and official Blu Rays always use a core because of compatibility.

To me it makes sense that the efficiency without a core would be higher, since the Core is there for compatibility reasons and the lossless part has to be put on top of that to encode the difference between the lossy and the lossless. I would think it's logically more efficient to just losslessly encode the entire signal, as you don't have to stack two codecs on top of each other. And the results, from my small number of experiments, seem to confirm that.

Part of the reason why it's bigger with a Core might be that encoding something with a lossy codec creates compression artifacts and if you're then encoding the difference between the lossless and the lossy signal, those compression artifacts in and of themselves become a kind of reversed "detail" that has to be encoded in the lossless difference signal instead of just encoding the full lossless signal itself.

As for TrueHD, it's entirely different if I understand it correctly. TrueHD Blu Rays tend to have an AC-3 fallback, but the TrueHD itself does not have a lossy core but is its own codec. Which is probably why TrueHD files tend to be smaller than DTS-HD MA files.

[schorman]

Interesting! Never tried that before.

Edit: Which version of the Encoder Suite are you using? The one I have does not allow "No Core" under the dropdown box for Core Bit Rate.

Edit #2: Just saw that it shows up when you set it to "Digital Delivery" instead of Blu Ray for compatibility.

[deleted user]

Alright, I decided to go a little bit more scientifically about this.

For one, I noticed that the "No Core" option isn't available for some channel configurations. For example, 4.0 doesn't appear to be possible without a core. Also I noticed that the "No Core" option only appears in the "Digital Delivery (.dtshd)" mode, not in the "Blu Ray disc" mode, so that again raises the question about Blu Ray compatibility, which I unfortunately can't test myself (lacking a burner/player).

As a little more advanced experiment, I took the Gremlins LD PCM and did a few DTS-HD MA encodes as well as a FLAC encode. For this I had to convert it to 48kHz, since DTS-HD MA doesn't appear to support 44.1 kHz. For the sample rate conversion I used iZotope 64 bit SRC.

Bit depth was left at 16 bit.

Results

PCM raw 44.1 kHz - 1.04 GB
PCM 48 kHz - 1.13 GB
FLAC raw 44.1 kHz - 487 MB
FLAC 48 kHz - 496 MB
DTS-HD MA No Core - 509 MB
DTS-HD MA 255kbps Core  - 644 MB
DTS-HD MA 384kbps Core - 670 MB
DTS-HD MA 768kbps Core - 766 MB
DTS-HD MA 1509kbps Core - 1.16 GB

Size of cores (extracted using TSMuxerGUI):
255kbps Core - 193 MB
384kbps Core - 291 MB
768kbps Core - 583 MB
1509kbps Core - 1.11 GB

Size of difference signal (rough calculation using the rounded sizes):
255kbps lossless difference: ~451 MB (~70 %)
384kbps lossless difference: ~379 MB (~56.6 %)
768kbps lossless difference: ~183 MB (~23.9 %)
1509kbps lossless difference: ~44 MB (~3.7 %)

It would be certainly interesting to do more tests with different types of sources and bit depths, but for now this is what I've done.

Especially Cinema DTS should be worthy of such an experiment too. I've noticed excellent compression rates of Cinema DTS using FLAC, so low that some people questioned me whether it was truly losslessly recompressed. I imagine coreless DTS-HD MA might be able to compete. This is why I've always argued against encoding Cinema DTS as lossy DTS; a 1509 kbps encode of a Cinema DTS track likely will be of similar size as a lossless FLAC encode.

I think the results are fairly interesting and nicely demonstrate the wastefulness of DTS-HD MA with a core. The 768kbps Core alone is already almost 100 MB bigger than a FLAC or coreless DTS-HD MA encode, and still needs 183 MB worth of difference signal on top of that to reach true losslessness.

Even with a mere 255kbps Core, the core almost approaches the size of a lossless FLAC encode, and the overall track is some 150 MB bigger than the pure lossless encode.

And at 1509kbps Core bitrate, the DTS-HD MA encode is actually bigger than the raw lossless PCM and more than twice the size of the pure lossless encodes!

[deleted user]

Interesting! Never tried that before.

Edit:  Which version of the Encoder Suite are you using?  The one I have does not allow "No Core" under the dropdown box for Core Bit Rate.

Edit #2:  Just saw that it shows up when you set it to "Digital Delivery" instead of Blu Ray for compatibility.

Yup, you have to choose Digital Delivery. And it doesn't work for some channel configurations, but does for the most important ones (2.0,5.1).

I only just found out about these limitations myself. Would be interesting what happens when such a track is nevertheless muxed into a Blu Ray.

Do you guys typically burn Blu Rays of projects or do you put them on USB sticks or whatever? I reckon that if it's just in an mkv and streamed to a receiver, it should still be able to decode it, since it's a perfectly fine official encode.

[bendermac]

7.1, 5.1, 5.0, 2.0 work without a core

[deleted user]

Alright, I did a quick experiment with the first reel of Two Towers Cinema DTS 5.1, decoded with the foobar2000 plugin, with the old version that also extracts the LFE:

Two Towers Cinema DTS Reel 1 16 bit 44.1 kHZ (48 kHz conversion using iZotope 64-bit SRC, as DTS-HD MA cannot be encoded at 44.1 kHz)

Results
PCM raw 44.1 kHz - 618 MB
PCM 48 kHz - 673 MB
FLAC raw 44.1 kHz - 209 MB
FLAC 48 kHz - 217 MB
DTS-HD MA No Core - 243 MB
DTS-HD MA 768kbps Core - 327 MB
DTS-HD MA 1509kbps Core - 393 MB

Size of cores:
768kbps Core - 112 MB
1509kbps Core - 220 MB

Size of difference signal (rough calculation):
768kbps lossless difference: 215 MB (~65.7%)
1509kbps lossless difference: 173 MB (~44%)

As I suspected, the 1509kbps Core alone is around the size of the FLAC encode, in this particular case even a little bigger. On top of that DTS-HD MA adds 173 MB to achieve losslessness when you use a core. The coreless DTS-HD MA sits at an acceptable 243 MB.

Note that this is 16-bit audio, and it's also a specific case. Cinema DTS has a full spectrum, but it's still a lossy codec (most here know this, but for anyone who doesn't). I think it's lossy in a very particular way that makes it easy to recompress, which explains the excellent lossless compression results that closely compete with the full-bitrate lossy DTS.

[bendermac]

I did also a test

Source: 24bit DTS-HD MA (2hrs16min)

Source DTS-HD MA with Core: 4.657.030.416 bytes
New DTS-HD MA without core: 4.086.208.096 byte
New FLAC: 4.020.259.960 bytes