Ask questions to Audio insider Sir Terrence

[Tok]

Originally Posted by srrndhound

Which does your statement mean?
1) The peak rate of the streamed compressed file can match the source PCM rate, or
2) The peak rate of the decoded output PCM can match the source PCM rate.

When decoded, the output is equal to the source PCM, correct? So the decoded stream is PCM at a constant bitrate. The peak rate of the compressed track MAY match the datarate of the source assuming a 0% compression efficiency for short bursts when the MLP/DolbyTrueHD codec rules cannot throw out or combine data. The FIFO buffer was done specifically to overcome DVD-A's shortcoming of max read rate of 9.6Mbps because a MLP stream with 6 channels at 24-bit/96kHz could hit peaks equal to the CBR of the source (13.8Mbps). Theoretically the buffers could be exhausted but MLP/TrueHD is a well designed codec that handles real world audio very well.

Again what I am saying is if the uncompressed source is 18Mbps the possibility exists that the peak data rate for the compressed track MAY BE 18Mbps.

Sounds to me like you are making assumptions that compression will always be greater than a 1:1 ratio so the the bitrate will always be lower than the possible maximum. Your example with a 10.2 makes sense in that the LFE channels would never require information above a certain frequency and there are periods of long droughts of LFE activity (ie. a lot of 0s can be thrown away and the sub channel bitdepth can be truncated in the stream).

[srrndhound]

Originally Posted by CraigW

Again what I am saying is if the uncompressed source is 18Mbps the possibility exists that the peak data rate for the compressed track MAY BE 18Mbps.)

Yes, that is a possibility when encoding pathological signals. We agree. All I am saying is that this is not the basis upon which 18 Mbps was selected for the TrueHD bitrate, as you have asserted. It is merely a coincidence, based on the fact that format makers decided to support 8ch/96/24. But as I have said, TrueHD is not constrained to that specific setup. It can use any bit depth from 16-24 in 1-bit steps, and a range of sample rates and channel configurations, all within the 18 Mbps boundary. We considered the entire scope of capabilities before we selected 18 Mbps.

Sounds to me like you are making assumptions that compression will always be greater than a 1:1 ratio so the the bitrate will always be lower than the possible maximum.

I only assume it because this has been born out in practice with DVD-A, and by all the TrueHD streams thus far encoded. None have reached as high as the source PCM rate.

[Tok]

Originally Posted by srrndhound

It is merely a coincidence, based on the fact that format makers decided to support 8ch/96/24. But as I have said, TrueHD is not constrained to that specific setup.

Okay, my bad. But I would be hesistant to use any lossless compression system that could not theoretically reach the max data rate that may be required. I never meant to imply that DolbyTrueHD was always 8ch/96/24.

The reason the MLP included the FIFO buffers was because peaks above the maximum DVD transfer rate could occur.

So I guess why did they limit DTHD to 18Mbps when there could be opportunities for BD audio discs where the full the BD transfer rate could be fully dedicated to audio? Imagine the possibilities...

What is the typical compression efficiency for DolbyTrueHD?

Originally Posted by srrndhound

I only assume it because this has been born out in practice with DVD-A, and by all the TrueHD streams thus far encoded. None have reached as high as the source PCM rate.

I would suspect that movie soundtracks compress more easily than multi-channel music tracks due to the fact that all channels are not consistently active at one time. Typically with movies the fronts take the majority of the workload where multi-channel music takes full use of all channels

[srrndhound]

Originally Posted by CraigW

But I would be hesistant to use any lossless compression system that could not theoretically reach the max data rate that may be required.

I'm not sure what you mean. As long as it compresses losslessly, how is that a problem?

So I guess why did they limit DTHD to 18Mbps when there could be opportunities for BD audio discs where the full the BD transfer rate could be fully dedicated to audio? Imagine the possibilities...

18 Mbps is a generous allocation for audio. Are you pining for Hamasaki-san's 22.2 system?

What is the typical compression efficiency for DolbyTrueHD?

About 2:1 for music, and at least 3:1 for movies, sometimes 4:1.

I would suspect that movie soundtracks compress more easily than multi-channel music tracks due to the fact that all channels are not consistently active at one time. Typically with movies the fronts take the majority of the workload where multi-channel music takes full use of all channels

Correct.

[Tok]

Originally Posted by srrndhound

I'm not sure what you mean. As long as it compresses losslessly, how is that a problem?

That's the key: as long as it compresses losslessly. A very complex multichannel recording may exceeed the max bandwidth. Again it is a very low probabilty, but still a possibility. It is just a personal opinion that I would not use it.

But realistically what are the chances we would ever see a BD with more than 8ch/24-bit/96kHz. Few very users out there even have a 7.1 setup and most users run out of space where to place additional speakers.

Originally Posted by srrndhound

18 Mbps is a generous allocation for audio. Are you pining for Hamasaki-san's 22.2 system?

Speakers everywhere.... And my amps go to 11

DD in the cinemas is over 15 year old. What are the chances that Dolby delivers a system to replace lossy DD with TrueHD at the local multiplex? I know that some digital cinemas are already using lossless, but is there a simple lowcost way to deliver TrueHD to traditional celluloid based cinemas.

It has gotten to the point that I rarely go to the cinema anymore because the picture and audio quality are lacking. I saw Kung Fu Panda(great movie BTW) with the kids and all I could think of was how much better the BD would be. The only theatrical experience I have been satisfied with in the last year was the IMAX presentation of The Dark Knight.

[srrndhound]

Originally Posted by CraigW

That's the key: as long as it compresses losslessly. A very complex multichannel recording may exceeed the max bandwidth. Again it is a very low probabilty, but still a possibility. It is just a personal opinion that I would not use it.

There have been times when MLP was not able to compress sufficiently to fit DVD-A. It was caused either by an excessively hissy source being quantized at 24-bits when 16 would have been more than generous, or ultrasonic birdies caused by a poor quality A-D. When it fails, the file is discarded. There is no "almost lossless" option.

But realistically what are the chances we would ever see a BD with more than 8ch/24-bit/96kHz. Few very users out there even have a 7.1 setup and most users run out of space where to place additional speakers.

I've seen a lot of new homes coming prewired for "surround sound" by putting 5 speakers in the ceiling. Install a normal 7.1 system on the floor and you've got 12.1, with the option for height. But until Sir Terrence and other mixers make soundtracks with height info, it's not easy to derive signals appropriate for those overhead speakers. But hey, 3D sound might be a nice companion to 3D movies.

DD in the cinemas is over 15 year old. What are the chances that Dolby delivers a system to replace lossy DD with TrueHD at the local multiplex? I know that some digital cinemas are already using lossless, but is there a simple lowcost way to deliver TrueHD to traditional celluloid based cinemas.

Digital cinemas use LPCM. I'm not aware of any using lossless. I'd guess the chances are zero that film-based media will find a way to carry 10x the audio bandwidth.

[Tok]

Originally Posted by srrndhound

Digital cinemas use LPCM. I'm not aware of any using lossless. I'd guess the chances are zero that film-based media will find a way to carry 10x the audio bandwidth.

It's amazing how advance a home theater has become in the last few years compared to the average multiplexes.

For a few thousand dollars, I have a better image, better sound, comfortable seats, and no sticky floors

[saprano]

I was talking about this terrence, yea i see a dialog normalization option, but they dont use it right? somebody on AVS posted this and said they do infact use it.

[gearyt]

Originally Posted by CraigW

It's amazing how advance a home theater has become in the last few years compared to the average multiplexes.

For a few thousand dollars, I have a better image, better sound, comfortable seats, and no sticky floors

and you can put the show on hold for "those" breaks of necessity

[gearyt]

Originally Posted by CraigW

Few very users out there even have a 7.1 setup and most users run out of space where to place additional speakers.

you'dd be surprised on how many of those we are...

I have 7.1 in my master bedroom !!

[didihala]

Originally Posted by gearyt

you'dd be surprised on how many of those we are...

I have 7.1 in my master bedroom !!

>>> you'dd be surprised on how many of those we are...<<<

Ahem... hear hear!

----------------------------
Pioneer PDP-5050HD
Sony STR-DA5300ES
Sony BDP-S300
Sony BDP-S550 (poor man's BDP-S5000ES)
etc., etc.

[Sir Terrence]

Originally Posted by saprano

I was talking about this terrence, yea i see a dialog normalization option, but they dont use it right? somebody on AVS posted this and said they do infact use it.

First my friend, stop arguing with people over there, save your breath. Second I would ask which titles have dialog norm used on them, so I could verify that they are correct. I cannot speak for the entire industry, but Disney has not used dialog norm on their titles with Dts HD MA as the audio codec.

[that1guystudios]

Sir Terrence...I've heard you work for Disney.
Are you aware of any restoration work being done on the audio or video for a Blu-Ray release of Mary Poppins? I know Terry Porter is working/getting ready to work on Fantasia right now, but I've been seeing a lot of info - some of which may be conjecture or rumors - about a full-blown restoration/reconstruction of Poppins from it's original elements,
since the last restoration left the colors slightly muted and the framing was incorrect. And from an audio standpoint, the 5.1 Home Theater mix added a lot of new sound effects. Speaking of which, do you know who mixed the 5.1 remix for Poppins' 40th anniversary DVD?

[dred]

Dear Sir,
Please keep reviewing Blu-Ray concerts. Personally, I think your reviews are spot on. The only knock I have against the Rush disc is that when I saw the tour, Geddy's bass was a little more ballsy and deep in person than on the disc. I know Geddy's tone could be considered "clacky" anyway, so it's not that big of a deal. Isn't having exceptional concerts on Blu-Ray great? Even better when it's a tour you saw and can go back to the disc to relive fond memories. Keep up the good work.
Kindred

[Sir Terrence]

Originally Posted by that1guypictures

Sir Terrence...I've heard you work for Disney.
Are you aware of any restoration work being done on the audio or video for a Blu-Ray release of Mary Poppins? I know Terry Porter is working/getting ready to work on Fantasia right now, but I've been seeing a lot of info - some of which may be conjecture or rumors - about a full-blown restoration/reconstruction of Poppins from it's original elements,
since the last restoration left the colors slightly muted and the framing was incorrect. And from an audio standpoint, the 5.1 Home Theater mix added a lot of new sound effects. Speaking of which, do you know who mixed the 5.1 remix for Poppins' 40th anniversary DVD?

I will check into any information about Mary Poppins(one of my favorite disney titles) and get back to you. I have been on a medical leave of absence since early December, so I am a little out of the loop at this moment.

If I am not mistaken Terry Porter did the remix for the 40th anniversary DVD. I could be wrong, but if I remember correctly(and that is suspect), he was slated for the remix work back then.

[Sir Terrence]

Originally Posted by dred

Dear Sir,
Please keep reviewing Blu-Ray concerts. Personally, I think your reviews are spot on. The only knock I have against the Rush disc is that when I saw the tour, Geddy's bass was a little more ballsy and deep in person than on the disc. I know Geddy's tone could be considered "clacky" anyway, so it's not that big of a deal. Isn't having exceptional concerts on Blu-Ray great? Even better when it's a tour you saw and can go back to the disc to relive fond memories. Keep up the good work.
Kindred

As a mixer, I realize there are times when the bass has to be throttled back to increase clarity and maintain balance in the mix. Aside from that, mixes headed for the harddrive or digital recorder are usually different than mixes created for the house. So while live you hear ballsy and deep, for the recording you may have a little more controlled less fat sound for the reasons I mention above. In all of the concert videos I have personally worked on, I have never seen the house mix ever used for a recording. The intent is so different, they probably would not translate as well in the home. When mixing for the live environment, you want a sound that is huge and impactful. A mix for the home has to be toned down a bit, as we sit closer to the speakers, and the speakers are not as large, and cannot move as much air as a line array used in live venues.

Thanks for the compliment on the reviews. Look for many more concert video reviews in the upcoming months. I have about 16 of them slated for review from all genres of music including classical.

[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...

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.

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?

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

Thanks for your time!

[Jeff Kleist]

Obviously sir T can give you what you're looking for

But you can do a Dolby TrueHD 192/24 5.1 track in 12mbps (half that)

And that's a fact

24mbps with a lossless compression should be more than adequate

[Ian_S]

Hi Jeff, it's not really about what real world bandwidth is required, more is it technically possible to have a lossy DTS-HD MA encode because you've exceeded the max bitrate.

I know it stretches reality a little to suggest there is something out there that will breach such limits, but let's suspend reality for a while.

I'll happily punt the question to Dolby TrueHD as well.

My understanding is that neither TrueHD or DTS-HD Master Audio support lossy encodes, but I'd like a definitive answer on that if possible from those who really know as opposed to those who think they do, and I'm not assuming you're the latter!!

[Jeff Kleist]

Uncompressed 192/24 audio is 28mbps at 5.1 channels. Just for reference.