Axiom Home Page Forums General Discussion Home Theater Dolby TrueHD and DTS Master HD question

Yeah and that's what I'm talking about. Although I understand that the end result is practically inaudible, the fact that it is compressed is to me not quite the 'ultimate'. IMO the uncompressed audio track is the absolute standard (it can be played at a higher bit rate, no?), and anything else is a step backward... it might be a 1 millionth of an inch of a step backward, but a step backward all the same. So what I'm wondering is, why did they stop where they did with the BluRay? Because it seems they left room for improvement. Which means somewhere down the road, whether it's 2 years, or 10 years or 20 years, they will come out with a new format and tout, "now you can listen to your movie soundtracks UNCOMPRESSED, along with full bandwith video"!!!

I don't see why they didn't just go ahead and do that now? It seems to me they stopped short of giving us everything we could ever want, just so they can upgrade it later. I'm sure they didn't have to stop where they did. They could have given the new disk 15, 20, 30% more volume to squeeze in everything it would take to give us the very best video along with uncompressed audio.

I'm quite sure that would have been possible. I guess we'll just have to wait for the next generation to come out.

No, you're still not grasping it. It isn't just "practically inaudible", it's exactly the same thing. Digital recordings(such as the CDs which we've had for almost 30 years)use the pulse code modulation(PCM)process. THD and MHD take the PCM bits and "squeeze" them into about half the space. Then when they're decoded("unsqueezed")what you have is exactly the same PCM bits that you got from the recording.

Additionally the lossless, compressed tracks can actually offer higher sampling rates than raw PCM, because there is a max-bitrate allowed for an audio track. At 192 kHz, 24-bit, with 6 channels (5.1; the sub-effects channel still has to be stored as full-range) PCM would exceed that, but TrueHD and DTS-HD MA with their compression can stay under the limit.

Think of it this way. What's better downloading a ZIP file of a document and unzipping it, or downloading the document straight? They are both the same in the end, because the ZIP file compression is lossless.

Ok I'm sorry, I thought it was the other way around. I thought the PCM was readable at a higher bit rate.

Mica, you may find this helpful with trying to grasp this stuff. I wrote it a while back when HD-DVD and BR was rolling out..... Some info is dated.

http://www.axiomaudio.com/boards/ubbthreads.php?ubb=showflat&Main=13094&Number=181379#Post181379

I tend to refer to lossless compressed sound like a Zip file.

We are all pretty familiar with Zip files. It is a way to take some files and compress them into a smaller space by removing unnecessary bits. You can often take a file and make it half as big as it was before.

When you unzip the file, it appears exactly the same as it was before. Your email, your word document, your family pictures, come out exactly the same as they were before you zipped them. If it was a lossy compression, you would lose parts of your emails and your kid's pictures would be without their face.

Lossless compression works the same way as zipping a file. PCM audio has a lot of unnecessary information that just takes up space but doesn't do anything. It is a pretty bad way to pack in your information. It is like letting your wife pack the van before a trip. She is probably terrible at it and fits it all in the van improperly and wastes space. When you go back in and pack the van yourself, you find all sorts of ways to pack the van with more efficiency to get more stuff in a smaller space. When you get to your destination, you didn't have to leave the dog behind because you couldn't fit it in the van.

So, there is no technical way that a lossless PCM track can sound any different than a lossless TrueHD or DTS Master soundtrack. The dog still has his nose and your email still says the same dumb gossip that it started with.

That said, even lossy compression sounds great to me. In a blind test with friends, not one of us could determine reliably what was lossy vs lossless. Could we determine a difference? Sure we could. Each had a slightly different sound. Most apparent was that each had a different volume level. But we couldn't determine which one was the lossless vs which one was the lossy. I don't bother myself with it. I will listen to whatever is the default track. I will even rip some disks to a player that can't pass HD audio and it makes no difference to me whether it is lossless or lossy.

On a side note, some of you also talk about video. I think it should be made clear that video is always compressed. A non-compressed hour of video takes something like 2TB. That is Terra Bytes. That is one of the largest harddrives available for each hour of video. A BD is most often compressed using the h.264 compression scheme which as you can see, results in a fantastic picture. it is pretty hard to find compression artifacts in many of the compressed h.264 video streams available today.

Ok, I'm starting to get it now. Thanks guys.

I'm quite sure in 10 years time we will have discs that are 100 percent uncompressed audio and video. I mean think back to the 80's and the Commodor 64... that was a 64 MEGA BYTE hard drive... a digital watch has more memory than that these days. Back then you wouldn't even fathom having an external hard drive that had two Terra Bytes worth of storage on it.

And at the rate of technology in 10 years time our cell phones will probably be able to pack 500 or so Terra Bytes in a mini-SD card. So by then we will have all the space available to put fully uncompressed video and soundtracks on one tiny disc. I wouldn't doubt it for a second.

Excellent explanation, autoboy. Especially the van part, although I see it when she packs the dishwasher. One minor quibble, with the family pictures. JPEG and GIF formats incorporate compression too. On a Mac in iPhoto (probably most other programs too) it asks what quality you want when you save it. Obviously higher quality = bigger files = less loss. You can tell when a GIF has too much loss - it gets blotchy. Interesting how the left brain stuff (music, pictures, video) tolerate loss and right brain stuff (words, numbers, programs) don't.

A Commodore 64 with a hard drive? I think I was in the wrong 80s!

Not to mention 64MB... that would have been outrageous then. It was 64K of memory.