audio settings - 5.1, downmixing, etc. 5 questions!

[hiohaa]

Okay. My vu+duo outputs to my amp via the hdmi and optical.
its a 5.1 amp. i am running the latest vix image.

Q.1 that means i turn 'digital downmix' off in the a/v options right?
Q.2 downmix is for people with 2 stereo speakers right?
Q.3 when i turn downmix On - the sound is much louder. Why?
Q.4 when im watching a film on say, bbc HD, you get a choice of 2 audio streams, mpeg and AC3. AC3 is the better one right?
Q.5 does AC3 output in 5.1? is it equivalent to DTS?

thanks.

[deckymckeown]

Okay. My vu+duo outputs to my amp via the hdmi and optical.
its a 5.1 amp. i am running the latest vix image.

Q.1 that means i turn 'digital downmix' off in the a/v options right?
Q.2 downmix is for people with 2 stereo speakers right?
Q.3 when i turn downmix On - the sound is much louder. Why?
Q.4 when im watching a film on say, bbc HD, you get a choice of 2 audio streams, mpeg and AC3. AC3 is the better one right?
Q.5 does AC3 output in 5.1? is it equivalent to DTS?

thanks.

1. Yes with your connection as you describe downmix should be turned OFF to get dolby 5.1 to output properly from vu+ duo to amp
2. Correct, downmix will turn the dolby 5.1 to off
3. Not sure, perhaps someone else can answer this one
4. AC3 is dolby digital 5.1 and yes is better quality
5. DTS is a different format than dolby digital. Some amps can play dolby only and not the DTS format like my panasonic surround system for example

[Rob van der Does]

3- AC3 has it's own volumelevel "encrypted" in the bitstream; as such it has nothing to do with a downmixed volume level (so indeed they can be different).
4- Hmm, can't say that AC3 is better per definition. Normally Yes, as modern movies tend to have much attention to sound quality. But when downmixing it, it may/may not be better then the MPEG-stream. But I doubt you will hear that difference.