Dolby Digital Help!

[Dave L]

I am currently taking part in a discussion over at the DigitalSpy Forum regarding the ability of Sony DigiBoxes to provide DD 5.1 sound and as I am getting a little out of my depth technically, I thought I would ask on here for a little clarification on my argument.

Backgroud
The Sony 760 DigiBoxes have an Optical Audio Out which currently supplys a PCM sound stream. It is being debated, whether it would be possible for this Optical Out to supply a DD stream instead, should one be broadcast by Sky. There is currently no way to select a DD Audio stream in the SkyDigital EPG and it has been argued that even if there were, because there is no onboard DD decoding in the DigiBox it would not be able to produce DD sound.

My Argument
I have said that, as I understand it, the DigiBox does not need to be able to decode/process the DD stream in any way, it only needs to be able to pass it onto an External Receiver for decoding and thus the ability to select a different Audio stream within the EPG software would provide DD sound to those of us with DD Receivers. I have based my arguments on old type DVD players which did not have any onboard DD decoding and required an external Receiver in order for the viewer to enjoy DD sound.

In a Nutshell
A digibox does not need any facility to process DD sound other than the ability to select which Audio Stream it outputs and a Digital Out to allow the encoded stream to be passed on.


Is this correct?

[sideshowbob]

Sounds eminently sensible to me. Whether it's factually correct or not, I've no idea.

[Cable Monkey]

If DD is broadcast, and there is no means of selecting sound, then DD programming may only be transmitted on channels enabled as part of the sky plus package. It would be the simplest way to do it, and unfortunately makes the Sony question mute. Anyone out there with greater technical knowledge of the system?

[Dave B]

I agree with you as well, the Sony box would need a software upgrade and then for Sky to pull their finger out :D

Dave

[Dave L]

The availability of DD on a non Sky+ system is not in question, simply the ability of the Digibox to pass on a DD sound stream without knowing anything about it.

It has been suggested that DD cannot simply be passed as a Binary stream and that the object that creates the Light signals for the Optical out would need to understand what a DD 5.1 output should look like.

Surely this is not correct as an Optical out produces an encoded signal not a decoded one. Why else does my DVD player have one optical out and 6 phone Audio outs for connecting to an amp. Is the first not for encoded and the second for decoded?

[MikeK]

If you remember, early DVD players couldn't ouput a DTS bitstream, even though one was on the disc.
I suspect it's the same with digiboxes.
Unless it's designed to specifically detect and lock onto a DD signal, I don't think it will handle it.

Don't forget, the actual sound transmitted for stereo now, is in MPEG (ie compressed) form, but is converted to PCM by the STB, for ouputting to a suitable amp.
With the decoder inside the STB, even if they sent 5.1 MPEG, at best it'd still only be decoded to stereo PCM, as that's all the decoder can do. At worst (which is what I believe), is that if they did send 5.1 MPEG, then you would get nothing, as the STB decoder wouldn't understand it.

Personally I think you are on a loser there - I can't see any way that older STBs will be able to output a DD 5.1 signal.

[Anthony.S]

I think Sky will send the DD soundtrack in a different MPEG stream much like a foriegn soundtrack on a DVD. Without a software upgrade there would be no way of telling the box which stream to output.