Audio Question for Gurus

[bluedog]

I'm new to MCE but I've had a bit of experience with DVB HTPC with other software (Nebula DigiTV).

Can someone please explain how MCE is handling the audio streams, as it seems very different to the way I've come to expect it.

My understanding of DVB is that we have a multiplex of SD and HD streams. OFTEN, the SD stream comes with an MPEG audio stream, and the HD stream comes with a DOLBY 2.0 audio stream. Each audio stream has its own clock that can be used to syncrhonise the relevant video stream to it.

I have a SPDIF connection to my Dolby Surround Amplifier. The amp tells me what sort of stream its getting. The amp recognises Dolby but it does not recognise MPEG audio. Software on the HTPC needs to convert the MPEG audio to PCM so that my amp can understand it.

So, with other (non MCE) software, I have noticed that when I watch SD channels, I usually see "PCM" on my amp. When I watch HD channels I usually see Dolby 2.0 on the amp (and, very occasionally, DD5.1).

With MCE however, if I select SPDIF (in Settings -> DVD -> Audio) and then watch an SD stream, my amp shows Dolby 2.0. But I would have expected to see "PCM" on the amp. Or are all the stations sending DD2.0 on SD now?

I'm very confused, and it seems important because I and a few others are noticing that audio is unreliable when in SPDIF mode. I find that I have to select "2 spkrs" for my audio configuration to get reliable audio (in this case, the amp sees PCM).

So the short question is - Why do I see DD2.0 when watching an SD channel? Shouldn't I be seeing MPEG converted to PCM?

The long question is - please tell me how MCE works all this.

If it makes any difference, I'm using PowerDVD 6 as my decoder.

Cheers
Simon

[arkay]

Hi Simon,

It's a good question and one I hadn't really put much thought into.

My take on it is that the stations are broadcasting DD2.0 which is reall yonly prologic in a DD stream as well as mpeg audio.

Prior to RU2 MCE had no concept of how to decode (or passthrough) a DD stream and MS puts some hacks in place with RU2 to make it work. SInce then I have always got DD2.0 on my amp on some SD channels. I say some because not all broadcast AC3 on SD.

You will only ever see DD2.0 on SD channels. 5.1 comes in only on HD which I think is what differentiates the two audio wise.

The mpeg stream IS still there but MCE is grabbing the DD2.0 in preference if it exists. The stupid thing is that there is no where in the interface to select a "preferred audio format" for watching and/or recording. Something I will definately be bringing up with the Vista Beta Team at MS.

Cheers,
Arkay.