Can someone explain DD 5.1 sound on iMac?

[imacken]

I have a new 27" 3.4GHz iMac and am confused by the sound.
I am using an optical cable from the iMac to a multi-channel receiver. When I watch a DVD in OS X, I don't get DD5.1 sound from my receiver, I can only force DPL by pressing a button on the receiver.
However, I do get DDD5.1 being automatically detected and decoded in my receiver when I use the same DVDs in my Bootcamp/Windows 7 partition!
Can anyone explain to me what is going on?
Thanks.

 

[NoKarma]

Using Perian or VLC might help there.

 

[imacken]

Thanks, Perian didn't help, but VLC did.
Why does VLC do DD but DVD Player (which shows DD Licence on the 'about DVD Player' menu) not?
All seems weird to me.

 

[NoKarma]

Take a look into the settings of the DVD app, there is a combobox that allows you to select how you want audio to be put out. See if there is a direct output option.

 

[imacken]

Right! I had looked into that before, and the 'Audio' option was greyed out in Preferences. However, when I tried again a couple of minutes ago, it was changeable and now it works!
I guess I must have been trying to change it previously when there was a disc playing.
Thanks a lot.

 

[imacken]

OK, I'm still confused here.
1) DVDs with DD5.1 play OK through DVD Player and the DD is detected on my receiver OK and full surround is working
2) if I try to get DD5.1 from audio files (with DD), I only get stereo
3) no games I've tried, e.g. Dragon Age 2, Portal 2, produce surround sound.
Even on Windows, if there was no native multi-channel sound, setting the receiver to 'Fourpoint 5.1 Mix' would produce a pseudo DD effect.
Why is this so difficult on a Mac?

 

[theSeb]

OK, I'm still confused here.
1) DVDs with DD5.1 play OK through DVD Player and the DD is detected on my receiver OK and full surround is working
2) if I try to get DD5.1 from audio files (with DD), I only get stereo
3) no games I've tried, e.g. Dragon Age 2, Portal 2, produce surround sound.
Even on Windows, if there was no native multi-channel sound, setting the receiver to 'Fourpoint 5.1 Mix' would produce a pseudo DD effect.
Why is this so difficult on a Mac?

It's exactly the same on Windows as in OSX. You have to change it in your sound preferences, if I recall correctly.

 

[imacken]

It's exactly the same on Windows as in OSX. You have to change it in your sound preferences, if I recall correctly.

No, you don't.
Any games, DVDs, etc. just play automatically in multi-channel sound in Windows.

 

[theSeb]

No, you don't.
Any games, DVDs, etc. just play automatically in multi-channel sound in Windows.

Hmmm. Is that new in Windows 7?

 

[theSeb]

Have you done this?

http://guides.macrumors.com/Configuring_5.1_Surround_Output_in_Mac_OS_X

Configuring the soundcard for discrete multichannel output

Most, if not all generic USB and FireWire audio devices default to 2 channel output in Mac OS X. It is very simple to change the settings in Mac OS X to allow for multichannel audio output:

Start "Audio MIDI Setup", located at /Applications/Utilities/Audio MIDI Setup
Change both the "Default Output" and "System Output" to your external device. If you would like to use the device as an input, also change the "Default Input".
Change "Properties for" to the external device
Click on "Configure Speakers"
Click on "Mulitchannel"
Select "5.1 Surround"
At these point connect your device to your amplifier or receiver. If you are unsure of which output goes to what input, do the following:

Have the device connected to the receiver, and the receiver set to the multichannel analog input
Click on the bubble that says "left front". This will play static out of the front left output, if the static is playing out of the wrong speaker, change your connections so that the static is playing out of the front left speaker. Remember that it only plays static for a short period, and you'll have to click the bubble again.
Repeat the above step for each other bubble until each bubble plays static out of the correct speaker.
Click "Apply" and "Done"
Mac OS X is now configured for multichannel audio playback.