Question about uncompressed PCM on Blu-ray

[Kev_85]

Ive noticed that when I watch a bluray and check the mb per second for the audio output its at 4.6 mp per sec. Although today I watched Flags of our Fathers and it was 6.9 I think. Is it just me or is these numbers low? I remember reading that DTS-MA can go as high as 25mb per sec, which is a huge difference from the numbers I mentioned

[GasCat]

Originally Posted by Kev_85

Ive noticed that when I watch a bluray and check the mb per second for the audio output its at 4.6 mp per sec. Although today I watched Flags of our Fathers and it was 6.9 I think. Is it just me or is these numbers low? I remember reading that DTS-MA can go as high as 25mb per sec, which is a huge difference from the numbers I mentioned

You're right they are fairly low. The numbers do vary throughout the movie. What audio output did you select in the setup menu of the disc?

[phloyd]

48000 * 6 * 16 = 460800 = 4.6 Mbps

48000 * 6 * 24 = 691200 = 6.9 Mbps

How many more bits are you looking for? For 6 channel audio, there are no more bits.

For there to be more bits you would need to have more channels or 96kHz or higher sample rate or both.

[hmurchison]

Originally Posted by phloyd

48000 * 6 * 16 = 460800 = 4.6 Mbps

48000 * 6 * 24 = 691200 = 6.9 Mbps

How many more bits are you looking for? For 6 channel audio, there are no more bits.

For there to be more bits you would need to have more channels or 96kHz or higher sample rate or both.

Exceeeeeeeellent. Gotta love posts where you know people have learned something. Thanks phloyd.

[powerSURG]

I'm going to sound like a total newb, but here it goes--I'm still using an old (3yrs) surround sound set up with an optical connection--I can set certain BDs to 5.1 PCM and see it register at 6.9Mbps on the PS3 but I'm wondering, can fiber/optical handle 5 channels of PCM? Am I confused??? lol Is my receiver just utilizing two channels while the PS3 pushes out 5?

[Zaphod]

Optical connections can only output 2 channel PCM. Optical connections do not have the bandwidth to carry 5.1 channel PCM.

[phloyd]

Originally Posted by GasCat

The numbers do vary throughout the movie.

This is not correct for PCM - the datarate does not vary.

[dobyblue]

PCM uncompressed uses a constant bitrate.

For 5.1 a 16/48 should register 4.6 Mbps and a 24/48 should register 6.9 Mbps.

16/48 7.1 PCM will register 6.1 Mbps.

We've seen DTS-HD tracks getting up past 3 Mbps on Reservoir dogs for instance.

You don't want the bitrate to be more than what the source provides for. DTS-MA and TrueHD will not use constant bit rates like PCM but rather variable bit rates. They are capable on Blu-ray of 24.5 Mbps but you won't see peaks that high until they're doing 24/96 7.1 encodes and even then I'd be surprised.

They're taking advantage of the bandwidth, don't worry. I'm sure at some point you'll see a 5.1 24/192 PCM recording done, likely for music, and that should get up pretty high. It would probably be audio only though.

24/192 7.1 PCM = 36.864 Mbps (too high)
24/192 5.1 PCM = 27.648 Mbps (maximum LPCM bandwidth)
24/96 7.1 PCM = 18.432 Mbps

The maximum LPCM support for an audio stream on Blu-ray as of March 2005 was listed as 27.648 Mbps. It can support PCM at 24/96 7.1 or 24/192 5.1

DTS-HD is limited to 24/192 at 5.1 and 24.96 at 7.1 as well with a bandwidth cap of 24.5 Mbps. However if 24/192 5.1 can be recorded in PCM and fit in the specs, great news!

http://www.blu-raydisc.com/assets/do...2955-13403.pdf

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[Kev_85]

Interesting replys. Thanks guys

[GasCat]

Very interesting. I was obviously looking at a different sound format. Thanks for the corrections Phloyd and Dobyblue.