Dolby Digital Or Pcm?

[astral]

Not strictly Thai related but..................

I find that some of my HD satellite channels here in the Middle East transmit a pure Dolby signal.

My Yamaha A1010 says fine, I do not have to do anything.

Other transmit a PCM signal and the decoder has to do the work..

Two questions I guess.

1. What does True transmit?

2. Does it really make any difference?

[David006]

Guess you might want to google digital sampling, PCM and Dolby for a good insight...

All signals through the air are analog..it is impossible to transceive digital format signals through air or space without a carrier like a laser beam.

Short range laser transmission of digital data signals ( 1gb ++) through free space is currently used in telecommunications but is subject to atmospheric degradation..........sort of like your tv remote.

...analog ( wavy line signal) are sampled/encoded (into square wave on/off signals ..all those 0s and 1s....reasonably analogous to Morse code maybe ) and then decoded.

.all use Pulse Code Modulation ( essentially the process of assigning a value to various points on the curves of analogue signals) in various schemes including Dolby digital.

Does it make a difference?....everyone says so but at the end of the day it is the receptors ( your eyes and ears) which must perceive the quality of the ultimate analog signal transmitted by your TV screen or speakers methinks..if your half deaf and blind like me ....then....lol

Anyways look it up if your interested ...all clever stuff

[Benjie]

Does the PCM come out in 5.1 or just stereo?

if it's 5.1 then PCM should be your best bet as it's uncompressed. However, generally it's always better to trust your ears.

[astral]

@David006

I think you misunderstood my question

I wasn't asking how it is done, just why.

Are there any TV's that can handle Dolby without a builtin decoder?

If not, I do not see the point of transmitting a DD signal. Better to

transmit PCM with embedded DD and let the user decide on the decoding box.

Strangely enough the sports channels, which are labelled as Dolby,

fail to light up the rear speakers at all.

Both DD and PCM film channels do contain surround data, though I have a feeling that

many films are being broadcast with stereo sound, even though the

video is HD

I will be asking the satellite provider for more info and explanation.

[tinfoilhat]

dolby digital has a whole lot of different formats, not all are surround.

also, it depends what your decoder is doing. my amp has a series of settings that allow you to play a 2channel dolby signal through 5.1 via a matrix plays certain frequencies through specific speakers for example mixing right and left channels to play through the center.

.

[astral]

It seems to be down to what the provider is putting on the audio stream.

A film can be in stereo, then the ads suddenly have surround.

Lazy technical work is my guess.

Same with sporting events, where surround would add to the atmosphere.

With the DD signal my amp just says Straight and that is it.

I can select different venue settings, 2 channel stereo or 7 channel stereo

but no access to the different DD or Neo settings

[samuijimmy]

It seems to be down to what the provider is putting on the audio stream.

A film can be in stereo, then the ads suddenly have surround.

Lazy technical work is my guess.

Same with sporting events, where surround would add to the atmosphere.

With the DD signal my amp just says Straight and that is it.

I can select different venue settings, 2 channel stereo or 7 channel stereo

but no access to the different DD or Neo settings

I've not used True visions in a about 2.5 years now, so no idea about what they provide anymore, but on Astro, some of the HD programs are broadcast in surround stereo...(HBO etc)...

I think it depends on the source provider not the local provider as to how these programs are broadcast. Some times the full surround can be a bit intense

I've got the telly set up through the speaker system so it does make a difference, if settings are correct... usually I find I can't be bothered!

[PattayaPete]

True broadcasts all channels with PCM sound and also Dolby Digital and Dolby Digital Plus on the HD channels.

PCM stand for Pulse Code Modulation and is a digital loss less format. It can contain two channels (stereo) or surround channels (5.1 surround sound). True do NOT broadcast PCM surround, it is always stereo or mono. Actually I don't think any broadcaster transmits PCM surround as it is bandwidth intensive.

The PCM sound can be encoded with Dolby Digital Pro Logic. True does this on some channels. Dolby Digital Pro Logic is a way to emulate surround sound and does a pretty good job of it. It is not as good as the true surround sound of Dolby Digital, but it's not bad. To receive the surround sound you need to have an amplifier or TV that can decode Pro Logic. If you don't then you will just get normal stereo.

As PCM is a loss less format it should sound the best however the DD Pro Logic will not be as convincing as a true surround format like Dolby Digital. CDs you buy in the shop are encoded with PCM stereo sound.

Dolby Digital is a true surround format. It contains 6 discreet channels often described as 5.1. They are Left, Centre, Right, Left Rear, Right Rear and LFE or Bass channel. To fit all this information into the signal it has to be compressed and so it is a lossy format. That means the sound you get is not exactly the same as the sound that was recorded. Similar to what MP3s do to CD tracks.

So Dolby Digital will not have the fidelity of a PCM signal but will have real surround sound. Most people can not hear the difference in fidelity so if you like surround then it is a good choice. Of course you will need an amplifier that can decode dolby digital to actually hear the surround channels.

Dolby Digital plus is a newer version of Dolby Digital and it improves the accuracy of the compression process making it less lossy than vanilla Dolby Digital. Once again you need an amplifier that can decode Dolby Digital plus to decode the signal.

Bottom line - if you are listening through your TV speakers or a stereo amplifier PCM is the best choice. If you listen through a multi channel home theatre amplifier Dolby Digital Plus will be your best choice if your amp supports that format (only newer ones do). If not then use Dolby Digital.

Edited December 14, 2012 by PattayaPete