5.1 Sound via HDMI in Steam OS?

[ChojinDSL]

Here's something I've been wondering about. I guess it's a bit of a niche issue, but then again considering that SteamOS and SteamMachines are intended for the living room, this might crop up more often.

I have a soundcard which has a Dolby Digital 7.1 and DTS 7.1 encoder chip, which allows any game with positional surround sound, to produce a dolby digital or DTS stream, which can be sent to a reciever via HDMI, coax or optical cable and then have the reciever decode it into separate discreet channels.

This only works for windows. As far as I know, this has to do with licensing issues regarding the Dolby Digital and DTS encoding codecs.
Under Linux you, with the same sound card, you would need to connect the six discreet analog outputs to the respective inputs of your reciever. If your reciever even has the required inputs.
e.g. Subwoofer -> Subwoofer, Front L/R --> Front L/R, etc.
This of course means a lot of cables going from your soundcard to the receiver.

How will this be handled on SteamOS and the SteamBoxes?
Will realtime positional audio be possible via HDMI or optical/coax like on consoles?
Will valve perhaps implement proprietary closed-source drivers for audio hardware, to deal with the licensing issue with regards to Dolby Digital/DTS?

[adolson]

On my Arch Linux desktop, I can output 5.1 surround over my GeForce's HDMI output.

SteamOS on this same machine seems to only do 2.0 stereo out, but I could probably find somewhere to change it if I poke around.

[darkkterror]

I'm not sure about potential licensing issues with Dolby Digital and DTS, but 5.1 or 7.1 Linear PCM should certainly be possible. In fact, 7.1 LPCM is all I really care about for SteamOS. I have a HDMI cable going from my Geforce GTX 780 to a 7.1 Onkyo receiver, but SteamOS currently only ouputs 2.0 stereo. I currently see no (easy and braindead-simple) way to change this. Right now I have to rely on my receiver's Dolby PLIIx mode to upsample the 2.0 audio to 7.1.

[m33k]

should be able to bitstream out and then the decoding would be done by the reciever, No license necessary.

[richi902]

5.1 LPCM works out of the box on linux, but only with nvidia driver.
to get 7.1 to work you need to edit a file somewhere, cant remember where exactly but it dosent work out of the box because the guy responsible for that(pulse audio?) dosent like the fact that 7.1 isnt a set in stone standart, eventhough everyone uses the same channel order.

[TheAngryMonkey]

I'm getting 5.1 surround with my GTX 550ti under SteamOS

[richi902]

how?

[ChojinDSL]

Keep in mind that I'm not talking about playing movies with a DD5.1/7.1 or DTS track. Thats just a passthrough to your optical/coax or hdmi output.

But I'm specifically talking about games and positional audio. e.g. Things that are behind you in the game, actually produce sound via the rear speakers, and such. Proper 3D sound when hooked up via reciever to multi-speaker sound system.

Most PC Gamer's setups (I imagine) simply have a surround sound set of computer speakers, which are hooked to the different analog outputs of their sound card. Usually, those are 3 jacks. Front L/R, Rear L/R and Center/Subwoofer.
In a case like that, dolby digital or whatever never is a factor, since the audio never goes to reciever via a single cable like coax/optical or hdmi.

In such cases, directX/directSound usually handles sending the proper audio to the separate channels.

Most onboard soundcards I've seen, don't actually have a realtime Dolby Digital encoder, and as such would only send Stereo Sound to your speakers IF hooked up via hdmi/coax/optical. This is ignoring movies, where the soundtrack is actually encoded to DTS or Dolby Digital. In such a case the Movie's audio track is simply passed through to the reciever, which then decodes the Dolby Digital/DTS stream.

As far as I know, this doesn't happen with games. I could be wrong of course, and maybe it was simply an odd combination of occurances that led me to believe it is indeed so.

Anyway, the way I work around it is, I have a dedicated sound card in my Gaming PC which has a feature (Dolby Digital Live I think it's called), where it encodes the discreet channels in realtime into a compliant dolby digital audio stream, when listening to the hdmi/coax/optical port.

The same dedicated sound card works under linux as well, but lacks the realtime dolby digital/DTS capability, due to restrictive licensing issues with the drivers.

[ChojinDSL]

I would be curious if anyone has actually managed to get proper 3D sound via HDMI/coax/optical under Linux or SteamOS when GAMING.

[adam.cluff]

I have noticed the same thing and even in Half Life 2 under sound options it only has 2 channel audio as an option as where If I run it in windows I have all the way up to 7.1. Would this be more of an Nvidia issue as the sound stream data transmitter is built into the video card?

[richi902]

i can use 5.1/7.1(7.1 adfter editing that specific file) fine on ubuntu desktop in games!
i have my nvidia gtx 650ti boost connected via hdmi to my sony receiver, and it shows 7.1 lpcm on its display. only valve games lack 5.1/7.1 support so far, its because valve dosent want to add it now, maybe in the future, they have said so on their github page. i have tested serious sam 3, euro truck simulator 2 and a few others all have 5.1/7.1 support.

[Toastmaster]

Originally posted by richi902:

i can use 5.1/7.1(7.1 adfter editing that specific file) fine on ubuntu desktop in games!
i have my nvidia gtx 650ti boost connected via hdmi to my sony receiver, and it shows 7.1 lpcm on its display. only valve games lack 5.1/7.1 support so far, its because valve dosent want to add it now, maybe in the future, they have said so on their github page. i have tested serious sam 3, euro truck simulator 2 and a few others all have 5.1/7.1 support.

Thanks for the info. All linux compatible games I own in steam are coincidentally 2D platformers or Valve games, so its really hard to know where the problem is originating. I'd say it's pretty frustrating that the Valve specific games don't support surround, since games like L4D2 are especially useful in surround. The game offers 5.1 channels but its for analog only. Personally, I'm using SPDIF, so I'm at a disadvantage where I can't rely on the same un-compressed PCM passthrough that HDMI uses.

[richi902]

surround over spdif is not supported on normal desktop linux. you can only use it to bit-stream movies to your receiver on linux via VLC for example. you either have to use a analog surround system with the 3? or 4? connectors which you plug into your back of the computer or hdmi.

[Phalkon13]

Normal sound cards will not push surround sound for games unless you have speakers plugged in via the 5 different analog audio jacks. You need a card that will re-encode (just NVidia card to HDMI or Optical will not work on normal video cards / sound cards).

There are cards out there that do it for Optical, but it doesn't sound as good as Analog cables.
(The Asus Xonar DX is one of them that does re-encoding for video games to support surround sound across the TOSLINK/Optical port)

[borg_7_of_9]

I'd also like to know as over HDMI I'm only getting 2ch I can set 5.1 but it seams no games are 5.1/7.1 CH even steamos is playing its crap sounds in 2ch