What is PCM

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matty_60618
Dolby Digital
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Joined: Sat Sep 06, 2008 8:36 pm
Location: Genoa City, WI

What is PCM

Post by matty_60618 » Sat Sep 06, 2008 8:41 pm

Can anyone give me an answer in laymans terms what PCM is and if it is better than TrueHD or HDMaster Audio?

DAve
LPCM
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Joined: Sat Feb 23, 2008 2:48 am
Location: Santa Clara, CA

Post by DAve » Sun Sep 07, 2008 9:39 am

PCM stands for Pulse Code modulation.

In reality the audio wave form is a continuously changing voltage level that eventually drives a speaker making sound.

For PCM, they take samples from the voltage 48,000 times a second - which is generally enough to 'join the dots' afterwards and recreate the original audio waveform accurately.

Sometimes they use 96,000 samples, which is considered better but obviously is twice as much data.

The samples are quantized to roughly 64,000 levels for 16 bit or 16M levels for 24bit PCM.

Both TrueHD and DTS-HD Master Audio will take this PCM data and compress it, conceptually in a way that will allow the original data to be recreated exactly.

So, conceptually both are identically equivalent to PCM.

On the down side, there are opportunities in TrueHD for example to add dialog normalization, which does make it sound different from the original PCM data.

On the downside for DTS-HD Master Audio, it appears that their method is so complicated, it is actually difficult to decode with the 'simple' micro processors found in BD players.

So, to summarize:

PCM is best, and is the format for the audio masters.

TrueHD and Master Audio are capable of being identical, but can present challenges of their own.

matty_60618
Dolby Digital
Posts: 2
Joined: Sat Sep 06, 2008 8:36 pm
Location: Genoa City, WI

Post by matty_60618 » Thu Sep 11, 2008 9:48 pm

Thanks DAve that helps clear things up. So then by those standards a disc with 7.1 PCM would be a better reproduction of the intended sound than one offering HD Master 7.1. I tend to find that 7.1 Master has heavy and sometimes overpowering base.

DAve
LPCM
Posts: 420
Joined: Sat Feb 23, 2008 2:48 am
Location: Santa Clara, CA

Post by DAve » Fri Sep 12, 2008 12:09 am

Conceptually they should be the same, but it seems that people do feel that there is a difference between them.

Some feel that there is some 'cheating' going on with DTS and it always seems 'louder' than Dolby encodes of the same material.

It is one of those little mysteries I guess :D

With TrueHD that uses the dialogue normalization function, there is no surprise that it sounds different...

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