Dolby Digital from computer

[marshalex]

I'm looking at a way of gettin dolby digital output to my home cinema speakers (sony HT-SS1100). I've got an Asus P6T mobo with optical and coaxial out. Would i need a new soundcard that supports dolby digital encoding or could i get software to do the same thing?

[CX23882-19]

Do you want Dolby Digital for movies or for games? For the former, you simply need to select SPDIF Passthrough if your DVD/video playback software. For the latter, I believe that you will need a sound card with something such as Dolby Digital Live (DDL). Some onboard sound chips support this too.

[marshalex]

games and watching videos. i've seen a few soundcards with built in dolby digital live. which ones are the best? dont really want to be spending much on one

[NightshadowUK]

Could you not just run an optical lead from your motherboard into the back of your DVD player and let that do the decoding?

[marshalex]

i have done this but it doesn't give dolby digital sound all the time. the only way i'm getting surround sound at the moment is by the prologic II encoding on the amp

[NightshadowUK]

It can only give Dolby Digital when the games / movies you're playing are kicking it out.

If it's receiving a stereo source your DVD player will use Pro Logic II to upmix the signal into surround sound.

[marshalex]

right fair enough. can i get a sound card that will encode the stereo sound into dolby digital, like the sound cards that come with dolby digital live?

[aidanjt]

Dolby Digital is just an encoding scheme for audio. 5.1 PCM works just as well through a S/PDIF connector.

[NightshadowUK]

Haha mate I think you mis-understand. To keep it simple I'm going to stick to 5.1 surround sound.

If compatible, the decoders in soundcards / AV receivers / Home Cinema DVD players do just that, decode the 6 channels of audio from a Dolby Digital / DTS track on a DVD and send the seperate signals to each of your speakers. You can't create Dolby Digital / DTS tracks, they have to already be present. All decoders do is unpack signals.

If a proper surround sound signal isn't present, there are techniques that exist (such as Dolby Pro Logic) which do their best to create 6 channels (5.1) from a stereo source, and while not perfect, they do a pretty good job of creating surround sound.

You're best option is to run an optical cable from your motherboard to the back of your DVD player. That way if you're playing something which has a Dolby Digital or DTS track present, it will decode it and you'll get perfect surround sound.

EDIT: 'CX23882-19' is right:

Dolby Digital Live converts any audio signal into a Dolby Digital bitstream for transport and playback through a home theater system. With it, your PC or game console can be hooked up to your Dolby Digital-equipped audio/video receiver or digital speaker system via a single digital connection, eliminating the confusion of multiple cables and ensuring the integrity of the audio signal.

Source: http://www.dolby.com/consumer/techno...olby_live.html

[marshalex]

ah right fair enough. i didn't realise it was all down to the signal. thanks for clearing that up

[NightshadowUK]

No problem matey, glad I helped.

[CX23882-19]

A single SPDIF link (i.e. a single coaxial or optical cable) only has the bandwidth to carry a stereo (2-channel) uncompressed stream. In order to send 5.1 down it, you must encode to a compressed format such as Dolby Digital (AC3) or DTS. This compressed DD/DTS stream is then decoded by the external receiver and output to your speakers.

With movies, the audio tracks are already in Dolby Digital or DTS format, so all you need to do is select "SPDIF Passthrough" (or simply "SPDIF") in your DVD software (e.g. PowerDVD or WinDVD). This will send the compressed stream from the DVD disc straight to your A/V receiver over the coaxial or optical cable.

With games, the audio is generated in real-time. In the case of surround sound this means that there are 6 independent uncompressed channels. These are then passed onto your sound card. If you use the analogue outputs on the sound card these channels are simply output to the appropriate analogue outputs.

If you use digital output on a regular sound card/chip, these 6 channels will be mixed down to basic 2-channel stereo. It may contain Dolby Pro-Logic or Pro-Logic II so that a suitable receiver could extract the surround information but it is not 6 discrete channels - it is still a stereo stream with matrix information. Pro-Logic can produce surround sound, no doubt about that, but the rear channel is mono and bandwidth limited (in terms of frequency response). I haven't tried Pro-Logic II but I believe it sounds better. Windows Vista will encode Pro-Logic (compatible) stereo if you enable "Virtual Surround". For Pro-Logic II you would need a sound card with support for it.

If you use digital output on a sound card/chip with "Dolby Digital Live", the 6 channels received by the card (from the game) are encoded into AC3 format by the sound card. The resultant stream contains 6 discrete channels of compressed audio similar to those on a DVD. DDL does create a Dolby Digital stream so that it can be decoded by an A/V receiver.

So, if you want 6 discrete full-bandwidth channels you need a sound card that can encode in Dolby Digital Live. The "true" Creative X-Fi cards (not the cheapest models) support this via a plugin that can be purchased from Creative. Some Realtek chips also support this but unless you see the option in the Realtek control panel on your system, yours probably doesn't.

Apologies if this is confusing, but the bottom line is that if you want true 6-channel audio from games over a digital connection you're going to need a card that supports Dolby Digital Live (DDL).

[Golden Dragoon]

AI haven't tried Pro-Logic II but I believe it sounds better.

A lot lot better, it is almost night and day the difference between them.

[Agent]

Dolby Digital is just an encoding scheme for audio. 5.1 PCM works just as well through a S/PDIF connector.

You can't dump 5.1 PCM uncompressed down S/PDIF, there is no where near enough bandwidth. The stream has to be compressed in some way. Most commonly Dolby Digital or DTS

http://forums.hexus.net/audio-visual...mp-please.html
http://forums.hexus.net/audio-visual...333-spdif.html

I've covered this a few times as it's a very confusing subject.

You can however put MPCM down a HDMI cable, but not optical.

I'm going to do a detailed sticky on this I think

[PodgePapin]

I got 5.1 for my blu-ray films from my pc to my Yamaha RX-V361 using PowerDVD, i got version 7 with my BD dvd drive, just a matter of selecting spdif in sound options (It didn't work at first but after playing about it works great now). Son't know about games yet though. And thats with my onboard sound too

[handscombmp]

You need to get a Dolby Digital Live Card.
Thats it.
End of story.

Depanding on your budget there are lots of them about but if you want a top notch one go for the Auzentech Prelude
If you want something cheaper butgood for gaming still (eg. EAX5) i'd get the Creative X-Fi Titanium (i'm planning to get this at one point as i'm in the exact same position as you)
If something a little cheaper still the Asus Xonar cards get very good right ups