What is PCM?

[gordon cunningham]

could anybody give me a short explanation of the difference between the main audio codecs: i dont know if this is the right terms


tru-hd?

what is PCM?

[bootman]

http://en.wikipedia.org/wiki/PCM

[HDJK]

In somewhat simpler terms :

PCM is the uncompresssed digital audio signal, which gets converted to analog by either the receiver or the player.

Dolby Digital or DTS are compression methods to lower the size and bandwith of the audio stream (resulting in quality loss).

Dolby TrueHD and DTS HD Master Audio compress the signal, but only in size (like a zip file) and get converted back to PCM; hence they are called lossless codecs.

So everything ends up as PCM before it gets converted to analog, just with loss or without.

[Blu-Style]

So,

#1
• PCM ist the best right ?

# 2
• DTS HD / True HD

#3
• DTS

[DealsR4theDevil]

Originally Posted by Blu-Style

So,

#1
• PCM ist the best right ?

# 2
• DTS HD / True HD

#3
• DTS

PCM and DTS HD / True HD are equal. DTS HD / True HD compress the audio track but in the end it is uncompressed or "decoded" back to PCM. DTS HD / True HD are compression methods that do not lose any quality. Dolby Digital and DTS compress the PCM as well, but those methods lose quality.

[Blu-Style]

Ah Ok.

Can you really hear the difference between those

Or do you hear it only with a really good 5.1 / 7.1 sound system ?

[DealsR4theDevil]

Originally Posted by Blu-Style

Ah Ok.

Can you really hear the difference between those

Or do you hear it only with a really good 5.1 / 7.1 sound system ?

Doesn't have to be "really good," but you do need a sound system with a receiver that can decode the lossless tracks (not all can). DTS HD / True HD compress the audio in order to save space. You need a reciever capable of decoding (uncompressing) those audio codecs.

[bkbluray]

If there is no quality difference between Dolby TrueHD, PCM, and DTS-HD MA, then why don't all studios release titles with PCM as a standard?

[gvortex7]

Originally Posted by bkbluray

If there is no quality difference between Dolby TrueHD, PCM, and DTS-HD MA, then why don't all studios release titles with PCM as a standard?

Because PCM is uncompressed and can take up a lot of space. Sometimes studios don't want to be in a situation where they have to compromise audio quality for video quality or either one of those because of extras/special features.

[Brain Sturgeon]

Originally Posted by bkbluray

If there is no quality difference between Dolby TrueHD, PCM, and DTS-HD MA, then why don't all studios release titles with PCM as a standard?

Space constraints. TrueHD allows for 2:1 to 4:1 compression without (theoretically) any loss in sound quality. I presume DTS-HD MA would have a similar compression ratio. If there is no loss in AQ, then this is a good thing, since you would have more space for more video, multiple audio soundtracks, extras, or what have you.

However, although these lossless compression codecs theoretically should sound transparent to the LPCM master, I don't think this has been completely proven in real world listening yet. Some of the listeners here have noted differences between TrueHD and the LPCM tracks on movies like 300 and the remastered The Fifth Element that happen to have both. Unfortunately, AQ is obviously a very subjective thing, so an objective measure of these things will be nigh impossible. It will also be interesting to see if there is a difference between THD and DTS-HD MA in real world listening-- the recent release of Spielberg's CEOTK has both of these tracks.

One of these days, I've got to try doing a detailed listening of the same soundtrack under LPCM vs THD vs DTS-HD MA to see if I can hear a difference.

[kknight]

http://forums.highdefdigest.com/showthread.php?t=3860

Dolby® TrueHD is Dolby’s next-generation lossless technology developed for high-definition disc-based media. Dolby TrueHD delivers tantalizing sound that is bit-for-bit identical to the studio master, unlocking the true high-definition entertainment experience on next-generation discs. When coupled with high-definition video, Dolby TrueHD offers an unprecedented home theater experience that lets you enjoy sound as stunning as the high-definition picture.

DTS-HD Master Audio is capable of delivering audio that is a bit-for-bit identical to the studio master. DTS-HD Master Audio delivers audio at super high variable bit rates -24.5 mega-bits per second (Mbps) on Blu-ray discs and 18.0 Mbps on HD-DVD - that are significantly higher than standard DVDs . This bit stream is so "fast" and the transfer rate is so "high" that it can deliver the Holy Grail of audio: 7.1 audio channels at 96k sampling frequency/24 bit depths that are identical to the original. With DTS-HD Master Audio, you will be able to experience movies and music, exactly as the artist intended: clear, pure, and uncompromised.

Uncompressed PCM 5.1: Found on a large number of Blu-Ray discs but not supported on HD-DVD, uncompressed PCM 5.1 is simply that: an uncompressed version of the film’s standard 5.1 to 7.1 soundtrack. This is exactly what the name says, uncompressed, raw audio.

----------------------------------------------------------------------------

I always thought DTS-HD Master Audio sounds the best.

[bkbluray]

Thanks. That makes more sense now.

[WickyWoo]

One of these days, I've got to try doing a detailed listening of the same soundtrack under LPCM vs THD vs DTS-HD MA to see if I can hear a difference.

The new Digital Video Essentials should have just that comparison on it

[Gio]

Originally Posted by gvortex7

Because PCM is uncompressed and can take up a lot of space. Sometimes studio don't want to be in a situation where they have to compromise audio quality for video quality or either one of those because of extras/special features.

thats another reason why HD-DVD sucks
they sacrafice audio quality for extras (look at transformers)
since their discs have limited space, comparred to BLU-RAY

[gvortex7]

However, although these lossless compression codecs theoretically should sound transparent to the LPCM master, I don't think this has been completely proven in real world listening yet. Some of the listeners here have noted differences between TrueHD and the LPCM tracks on movies like 300 and the remastered The Fifth Element that happen to have both. Unfortunately, AQ is obviously a very subjective thing, so an objective measure of these things will be nigh impossible. It will also be interesting to see if there is a difference between THD and DTS-HD MA in real world listening-- the recent release of Spielberg's CEOTK has both of these tracks.

Audio quality differences between PCM, TrueHD and DTS HD are determined by what bitrate they're encoded at on specific movies. All things being equal, they should all sound about the same. It has been my experience that many listeners/viewers don't have the right equipment to be able to fully test all those audio formats thus thinking that one is superior to the other when in fact that may not be the case.

[gvortex7]

Originally Posted by Gio

thats another reason why HD-DVD sucks
they sacrafice audio quality for extras (look at transformers)
since their discs have limited space, comparred to BLU-RAY

But, I believe HD DVD still thinks to this day that the 30GB max capacity is more than enough to hold a high quality (bitrate) audio/video encode and some special features on one disc. That seems a bit naive.

[gordon cunningham]

when i asked this question initialy, i thought i might get an explination that would leave just staring at the screen. but the main man (HDJK) has come up trumps for lakies like myself. give the man a clap

[Brain Sturgeon]

Originally Posted by gvortex7

Audio quality differences between PCM, TrueHD and DTS HD are determined by what bitrate they're encoded at on specific movies. All things being equal, they should all sound about the same. It has been my experience that many listeners/viewers don't have the right equipment to be able to fully test all those audio formats thus thinking that one is superior to the other when in fact that may not be the case.

Agreed. The issue with the word length is also a bit confounding. I think there have been BD's (The Fifth Element maybe?) where the LPCM was 20 bit and the THD soundtrack was 24 bit, but they both derived from an identical master. How much does this impact the two if they are born of the same "father"?

The volume setting of the individual tracks can also have a huge impact on your perception of the sound. Just a couple of dB difference can make it sound like one track is much better than the other, and there usually is a bit of a difference in SPL between each of the soundtrack. Matching the levels with an SPL meter when comparing tracks becomes very important to eliminate this perceptive issue.

Originally Posted by WickyWoo

The new Digital Video Essentials should have just that comparison on it

I've got that one on my list (even if Joe Kane seems to be pro HD-DVD, or, at least, was in the past). That one, 300, TFE, and, CEOTK are on my "compare soundtrack" list, if I can ever get the time to do this. Hell, I've still got a stack of about 25 BD's sitting in their shrinkwrap.

My audio rig is pretty discerning, so if there is a difference between these tracks, it should be noticable-- of course, there is the issue as to whether my ears are discerning enough.

[gvortex7]

The volume setting of the individual tracks can also have a huge impact on your perception of the sound. Just a couple of dB difference can make it sound like one track is much better than the other, and there usually is a bit of a difference in SPL between each of the soundtrack. Matching the levels with an SPL meter when comparing tracks becomes very important to eliminate this perceptive issue.

Very true as well.

[jorg]

pcm or lpcm is the penical of audio lol its totaly uncompressed meaning no qaulity loss in compresion