Ask questions to Audio insider Sir Terrence

[Sir Terrence]

Originally Posted by Ian_S

Somewhere else, not AVS for once, someone is claiming that DTS-HD MA is not always lossless, and that if (somehow) you have a source that requires more than 24.5Mbps, the codec will deliver a lossy mix at 24.5mbps...

From my understanding of the codec, I do not think this is true.

Now I don't see how DTS could describe the DTS-HD MA extensions to the core as lossless extension if the above is true.

The spec describes the encoder as lossless up to 24.5mbps. It does not say anything about bitstreams above 24.5mbps, and quite frankly, bitstreams that large cannot be handle by ANY of the lossless codecs. I cannot see any instance where you need any more bandwidth that each of the lossless codecs offer.

So, my question, daft as it seems is a) is DTS-HD MA guaranteed lossless to whatever you put into the encoder, and b) if you exceed the available bandwidth will the encode just fail, and leave it up to you to manipulate the source to reduce it's bandwidth requirements?

As far as I know, "B" is the right answer. "A" is not possible as the spec of the codec only supports bitstream bandwidth up to 24.5mbps

Sorry if it's a daft question, but I would like a categoric answer if possible...

Thanks for your time!

Ian, this is a pretty useless angle for an arguement. Honestly, I can see no situation where you need a bitstream that is greater than 24.5mbps. That is an awful lot of data that would need to be stored. There is no way you are going to get that much audio data on a disc without the video suffering greatly. At 24/96khz spread out over 6 channels, that would equal to 4 bitstreams running simultaneously. Can you really see a need for that?

[mark antony]

Hi Sir Terrence,

I realise it's a year off, but as Fantasia (&2K) are due next year, do you know what Disney is planning to do about the audio on Fantasia?

I know the current dvd is a marvel given the limitations of the surviving audio sources, but i'm sure any kind of lossless track is gonna show up the flaws even more, might they give us the 1982 re-recording as an alternate track or even re-record it again as they're are supposedly numerous issues with that (apart from it not being Stokowski!)

Thanks

M

[Sir Terrence]

Originally Posted by mark antony

Hi Sir Terrence,

I realise it's a year off, but as Fantasia (&2K) are due next year, do you know what Disney is planning to do about the audio on Fantasia?

I know the current dvd is a marvel given the limitations of the surviving audio sources, but i'm sure any kind of lossless track is gonna show up the flaws even more, might they give us the 1982 re-recording as an alternate track or even re-record it again as they're are supposedly numerous issues with that (apart from it not being Stokowski!)

Thanks

M

Mark,
I know that Terry Porter is working on the project, but I do not have any more information than that. When I get back to work (I am on medical leave), I will make sure to get more information to bring back here.

[Ian_S]

Thank-you for your reply Sir Terrence.

I totally agree that ever getting to having 24.5mbps of compressed bitstream audio is rather unlikely, but such are discussions when someone claims that DTS-HD Master Audio is not always lossless.

Rather than increasingly pointless 'debate', I just wanted a categoric answer that DTS-HD MA was infact always lossless. Not sure if I have that or not.

The quotes I was surprised by are:

BTW, dts hd MA is often mistakenly believed always to be lossless, but pedantically, this is not true. dts hd MA supports lossless encoding (6 channels up to 192 kHz, 24 bit or 8 channels at 96 kHz, 24 bit), but does not actually make any guarantee: a dts hd MA track may legitimately be lossily compressed. This can be contrasted with Dolby TrueHD, which is lossless by definition. In practice, current Bluray disks with dts hd ma typically are losslessly compressed, but we may well see this change as providers scramble to get multiple languages and extras on to a single disk, at the cost of quality.

The point is not that dts hd MA is not lossless, but rather than the actual spec doesn't insist on lossless encoding - it permits a lossy encoding. It's carefully formulated in the general marketing papers like this (quote from the white paper, accent from me):

If you think about the dts hd MA encoding:

then you can see that this contradicts the requirement for guaranteed losslessness (e.g. Meridian Lossless Compression).

A compression scheme can only reduce the size of some of its possible inputs, at the cost of others. You can't squeeze 2**n possible bit patterns of length n into less than 2**n bit patterns, except by discarding bits.

The trick in compression algorithm design is to recognize the more common domain-specific "patterns", at the cost of rare ones. The end result however remains that the maximum output size of any compression algorithm is at least 1 bit longer than its input (you can always choose an input pattern that forces expansion). Any system that allows imposition of a maximum data rate that is lower than its inputs is necessarily not guaranteed to be lossless.

As I said, I was being pedantic; for all practical purposes current Bluray films with dts hd MA tracks are losslessly encoded. I do not own a crystal ball.

If anyone knows someone from DTS who might care to comment it would be useful

[Sir Terrence]

Originally Posted by Ian_S

Thank-you for your reply Sir Terrence.

I totally agree that ever getting to having 24.5mbps of compressed bitstream audio is rather unlikely, but such are discussions when someone claims that DTS-HD Master Audio is not always lossless.

Rather than increasingly pointless 'debate', I just wanted a categoric answer that DTS-HD MA was infact always lossless. Not sure if I have that or not.

The quotes I was surprised by are:

If anyone knows someone from DTS who might care to comment it would be useful

Ian,
This you can just dimiss as technobabblespeak. If you compare the waveforms of a lossless PCM stream, and an identical encoded Dts-HD master audio stream, they are identical in every way. This is just Dolby fanboyism on techno steroids. There is no need for anyone from Dts to comment on this bull. Walk away from this quickly, there are other things in audio to focus on instead of a carrier codec. Both DTHD and Dts-HD MA are lossless, and there is no "more lossless than the other" point to make on this.

The master audio extension is built off the core data at a bit rate of 1509kbps. It cannot be built off of any bit rate but that one. The scaleable charactistics of the core do not come into play in this example because only one data rate can be used with the lossless extension. Secondly, most releases do not have a ton of languages on disc. I have seen some disc with a ton of languages, and they also included a PCM uncompressed track as well which is less efficient in many cases to Dts-HD MA. So all of the arguements made in those comments are not realistic in the real world.

[PeterTHX]

Originally Posted by Sir Terrence

The master audio extension is built off the core data at a bit rate of 1509kbps. It cannot be built off of any bit rate but that one.

What about the few titles like Suburban Girl and some European ones that use the DTS core of 768kbps?

[mark antony]

Originally Posted by Sir Terrence

Mark,
I know that Terry Porter is working on the project, but I do not have any more information than that. When I get back to work (I am on medical leave), I will make sure to get more information to bring back here.

Thanks, hope you get well soon

[Sir Terrence]

Originally Posted by PeterTHX

What about the few titles like Suburban Girl and some European ones that use the DTS core of 768kbps?

Peter,
If the film is mostly dialog, and places little or no demand on the encoder moment by moment, it may only take a core bit rate of 768kbps to maintain lossless. Using the 768kbps core as the foundation for lossless encoding allows for the encoder to run losslessly at a variable bit rate that is less than 1.5mbps core for far less demanding mixes. This does not make the audio lossy just because it runs at that rate. The soundtrack may only need a peak data rate of 900kbps to maintain losslessness during its more demanding passages, so there is no need for a 1.5mbps core.

I don't dwell on exceptions, I dwell on common practice. Only fanboys pick such irrelevant points like this to dwell on. You and I know that common practice has shown that 1.5mbps is the only "core" used in most releases. Aside from that, it may not always take a core data rate of 1.5mbps for a soundtrack to be lossless. It is all in the moment by moment demand the signals place on the encoder right?

[Jeff Kleist]

A good thing to look at is how a VBR FLAC encode runs on the winamp bitrate meter. I've had spoken words stuff running as low as 78kbps

I recently got the German Death at Funeral Blu, and the German dub is DTS-MA while the English is vanilla DTS. They sound identical, except for the bad acting, unnatural sound and general disagreeableness of a dubbed film that is all about the post work on that dialog. Musical passages and non-dialog is essentially the same.

That's the same reason why you can fit a "quiet" 2.5 hour film with lossless on a BD-25 and not worry about it. Less bits for the same result

[PeterTHX]

Originally Posted by Sir Terrence

I don't dwell on exceptions, I dwell on common practice. Only fanboys pick such irrelevant points like this to dwell on. You and I know that common practice has shown that 1.5mbps is the only "core" used in most releases. Aside from that, it may not always take a core data rate of 1.5mbps for a soundtrack to be lossless. It is all in the moment by moment demand the signals place on the encoder right?

Highlighted what I was asking about:

The master audio extension is built off the core data at a bit rate of 1509kbps. It cannot be built off of any bit rate but that one.

I know if it's an MA track, it's lossless. What I was asking about was your statement that the core must be 1536 and cannot use another yet there are tracks that use 768 as the core rate. Rare, but they exist. Just as I've seen companion TrueHD tracks at 448 kbps instead of the recommended 640.

[Bobby Henderson]

Originally Posted by PeterTHX

What I was asking about was your statement that the core must be 1536 and cannot use another yet there are tracks that use 768 as the core rate. Rare, but they exist.

Peter, I don't know why you keep bringing up that point other than to make a negative comment about DTS. The BDs you mention with those 768kb/s cores are niche titles, not mainstream Hollywood releases.

Until American studios commonly using DTS-HD M.A. (like Universal, Fox, Lionsgate, etc.) start using 768kb/s cores in some sort of sporadic or even commonplace fashion the DTS-HD Master Audio format is not going to be a low bit rate minefield that viewers with older receivers need to avoid.

[PeterTHX]

Originally Posted by Bobby Henderson

Peter, I don't know why you keep bringing up that point other than to make a negative comment about DTS. The BDs you mention with those 768kb/s cores are niche titles, not mainstream Hollywood releases.

You're looking at something that's not there.

I simply asked if they have to be 1536 how can others be 768, albiet rare, niche or whatever.

I never said it wasn't lossless or anything.

If anything, there was a rumor that MLP (on which TrueHD is based) wasn't always lossless. Not true of course.

[Penton-Man]

Welcome back Sir T.

[Sir Terrence]

Originally Posted by PeterTHX

Highlighted what I was asking about:



I know if it's an MA track, it's lossless. What I was asking about was your statement that the core must be 1536 and cannot use another yet there are tracks that use 768 as the core rate. Rare, but they exist. Just as I've seen companion TrueHD tracks at 448 kbps instead of the recommended 640.

My angle was not that it cannot be done, its that it is not done as a common practice. The common practice for use of Dts-HD MA is to use the 1509kbps core. 1536kbps is not a data rate used on DVD, and quite frankly neither is 768kbps. Using the 48khz sample rate, 754kbps is the lower core data rate used. 768kbps is used for the 44.1khz sample rate found on laserdisc.

[Sir Terrence]

Originally Posted by Penton-Man

Welcome back Sir T.

Gee, Thanks PM LOL

[PeterTHX]

Originally Posted by Sir Terrence

My angle was not that it cannot be done, its that it is not done as a common practice. The common practice for use of Dts-HD MA is to use the 1509kbps core. 1536kbps is not a data rate used on DVD, and quite frankly neither is 768kbps. Using the 48khz sample rate, 754kbps is the lower core data rate used. 768kbps is used for the 44.1khz sample rate found on laserdisc.

Ah. So 754 can be used as a core.

I guess it saves a couple of gig of space, and a tad more bandwidth.

I was thinking and I'm sure the rumor of DTS-HD MA not being lossless comes from several manufacturers referring to both DTS-HD HR (lossy) and DTS-HD MA (lossless) as simply "DTS-HD"

[Sir Terrence]

Originally Posted by PeterTHX

Ah. So 754 can be used as a core.

I guess it saves a couple of gig of space, and a tad more bandwidth.

I was thinking and I'm sure the rumor of DTS-HD MA not being lossless comes from several manufacturers referring to both DTS-HD HR (lossy) and DTS-HD MA (lossless) as simply "DTS-HD"

754kbps can be used as a core if the maximum overall bit rate remains below 1.5mbps to save space. The ability to use a variable bit rates below core 1509kbps does save a bit of space on the disc. However I would not recommend using this core bit rate with alot of action going on. In practice it is usually best to stick with 1509kbps core bit rate for MA lossless.

[Marquoz]

Sir Terrence,

You seem more knowledgable about the digital conversion then most other people. I was driving home wondering about natural disasters. I live in New Orleans, and after Katrina, a lot of people purchased generators. If its large enough, people will have power via generators, but no access to cable. Those people won't have a digital converter, so I was wondering is there a provision to allow TV companies to temporarily broadcast on the analog channels during an emergency to get the EBS out to more people, or are those people with cable basicly out of luck, and have to rely on a radio?

David

[Joe Cain]

Originally Posted by Marquoz

Sir Terrence,

You seem more knowledgable about the digital conversion then most other people.

On a related note, a buddy of mine is TD at a local theatre complex and it was only this week he realized he needed to investigate whether or not their Shure & Sennheiser wireless mics were going to be affected by the local broadcast transition. I hadn't thought about it---my only wireless gear are some inexpensive in-ear monitors which have fallen out of favor---but as I poked around on Sennheiser's site checking on available frequencies for given equipment in various locales, I wondered: could this transition could be a nightmare for unprepared bands or stage productions on tour?

[Sir Terrence]

Originally Posted by Marquoz

Sir Terrence,

You seem more knowledgable about the digital conversion then most other people. I was driving home wondering about natural disasters. I live in New Orleans, and after Katrina, a lot of people purchased generators. If its large enough, people will have power via generators, but no access to cable. Those people won't have a digital converter, so I was wondering is there a provision to allow TV companies to temporarily broadcast on the analog channels during an emergency to get the EBS out to more people, or are those people with cable basicly out of luck, and have to rely on a radio?

David

David, they are basically out of luck, or have to depend on radio. After the switch over takes place, the spectrum for analog broadcast will be(or is already) auctioned off.