Optical Digital Connection

[stigweed]

I've got a beautiful 5.1 Sony DVD/Radio system (DAV-S400). The only audio inputs are 2 separate stereo analogue phono connections and an optical digital connection.

I can't find any info on the optical connetion. I don't know if it supports 5.1 or just stereo? I heard the the Sony PS2 has a 5.1 digital optical output is this true? Does anyone know if this is likely to be a 5.1 input on my DVD system?

If so, the next step is optical out on my soundcard. I've got 5.1 through the separate analogue jacks on the motherboard, but there's also an SPDIF header on the board. I heard somewhere about an SPDIF->Optical converter - is this even possible or do they carry completely different data formats? I'd rather not shell out for a semi-pro Audigy type thing with the drive bay with all the knobs and connectors when all I want is the optical output.

edit: OK I've found the converters on maplin but it doesn't say if it'll carry 5.1, it just says suitable for home cinema. Next step is the spdif riser card, can't find any in the UK yet.

The idea being Doom3 in 5.1 without shelling out for another set of (inferior) speakers when I've already got Sony wired round my room. Saves on wires, saves on money can't wait to get freaked out when the slipgate to hell opens up in my bedroom. Good luck trying to sleep, neighbours...

Edit2: Found some for Gigabyte Motherboards. My mobo manual says which pin is + and which is - so I can always bodge it...

[cadaveca]

i've got the answer for you
you'll never get 5.1 from a game digitally to your stereo....i spent over 2000 on my sony stereo hoping i would be able....i have both digital and analogue 5.1/6.1 inputs...the digital allows my stereo to do the processing, the analogue is just a stright passthrough to the individual amps.....but hte problem is this...D3D does not deal with sound digitally...so unless your games say DTS sound on them..you have to go analogue.
you can get 2CHANNEL STEREO whilst palying your games, and then let your stereo do some environment processing to get the sinutaed surround, but you won't hear individual footsteps in either of the rear channels.. it'll just be louder in one than the other.
i'ma sound purest....using 6 guage wire for all my speakers should help you understand just how important sound clarity is to me...
i'm the resident gigabyte guy u guess... and eventhough i have a pro2 ...even the nnxp does not offer D3D digital surround sound....that's up to the game maker and microsoft.

[cadaveca]

spdif is sony/phillips digital interface.....and you'll only get stereo digital.. i don't think i was clear on that. dvd's you might get surrond on...but you have to connect both the analouge stereo connections as well as the coaxial line to get the signal there properly. i don't understand this, as i don't have to do that with my audigy, but i do with the gigabyte onboard.

[cadaveca]

and yes, you can connect the ps2 and get true 5.1 to your dream system...
it's really all about the sender's source when it comes to spdif...the type of input has no real bearing. all spdif input/output will do 5.1....@ 44.1khz.

[Aedan]

SPDIF and Optical are actually the same thing, just one as electricity and one as light. They're compatible, so the converters will work.

The nForce 2 boards with Soundstorm (MCP-T) can create a Dolby Digital stream (AC3). I've personally done this, so I know that it works.

[cadaveca]

but does it do it in a game? i doubt it.
i tried to get a shuttle sn45g with the soundstorm to do the optical thing to my stereo(sony str-db930) and it was no go....
but...aedan..if you CAN get D3d 5.1.....PLEASE LET ME KNOW HOW!
ac-3 is fine optical..but it only nets you 4.1 in D3d..not 5.1

[Aedan]

Originally Posted by cadaveca

but does it do it in a game? i doubt it.

Yup, works fine in game. Set up the Dolby Digital Encoding, enabled Create Center Channel, Create LFE Channel. That's 5.1

[cadaveca]

ahh.... then you are not getting dolbydigital 5.1....you are getting dolbysurround 5.1....
i thought that there was no difference, but i got an awesome demo @ the hometheater place that I normally shop at, and boy, does the spatialization effects ever differ.
i have a coaxial to optical converter..no diff...
so i guess yes, you are getting 5.1....but it is not the same effect as taking the 3 1/8th inch jacks and going direct for me....but who knows...could just be my stereo....but i am not into believing that....


what you are doing is having the onboard (soundstorm) do the processing...i wan my STEREO to do the processing....i paid that 2000 so that i could have the option. I haven't tried my turtlebeach card yet tho....

[cadaveca]

which brings me to what my point was.....you are still not going to be able to get that 5.1 if you have a gigabyte board and no other soundcard...yes, if you have soundstorm you can get 5.1...but most likely it won't all make it to your dream system.....like i was saying..for it to work you need both the analogue and the coaxial connectors for a gigabyte board to do spdif PASSTHROUGH...which is the best that gigabyte has to offer. this connection scheme is not a valid one for dreamsystems.

[stigweed]

OK I'm getting slightly confused. You're saying the SPDIF or optical output will never be in proper dolby digital from i)games (because of D3d), ii) any soundcard (even if there's software doing it for you) or iii) just the gigabyte motherboard?

I looked into the Asus motherboard I've got. The CMI8378 chipset for the sound only does stereo on it's spdif output. It's a common chip, maybe that's why you're needing to use the analogue as well? (was going to nick my Dad;s GF's soundcard as it has an spdif plug but its the same chipset).

I've found a gamers sound card (i.e. cheapish at ~£30) the Terratec Aureon 5.1FUN or something which seems to have some good reviews (considering it's so cheap, got editors choice at one site) and it has an Optical connector on the back panel.

Suppose I bought this. Are you saying that D3d software and games would only do dolbysurround 5.1 and not the superduper dolbydigital5.1? What about Doom3 which from the start was always going to do true 5.1 (through EAX if I remember???) -would that work? Are you saying that technology demos and DVD software would produce true dolbydigital5.1 on the SPDIF?

To be honest, with the older games, I'm not bothered about true surround but Doom3 and HL2 are going to rock with it.

one review: http://www.pcw.co.uk/products/hardware/1139957

[stigweed]

Originally Posted by cadaveca

but i got an awesome demo @ the hometheater place that I normally shop at, and boy, does the spatialization effects ever differ.

could that be because they were showing you an amazing system? Or was it truly because of the format? My DVD is only a budget system but it's still pretty good and is probably better than most of the 5.1 setups that are sold from computing/gaming type sites. That's the kind of quality I'm looking for, but true separate channels would be good rather than as you said having one rear speaker do something louder than the other

[cadaveca]

Originally Posted by stigweed

OK I'm getting slightly confused. You're saying the SPDIF or optical output will never be in proper dolby digital from i)games (because of D3d), ii) any soundcard (even if there's software doing it for you) or iii) just the gigabyte motherboard?



Suppose I bought this. Are you saying that D3d software and games would only do dolbysurround 5.1 and not the superduper dolbydigital5.1? What about Doom3 which from the start was always going to do true 5.1 (through EAX if I remember???) -would that work? Are you saying that technology demos and DVD software would produce true dolbydigital5.1 on the SPDIF?

ok..sorry for the confusion, but there are many things at play here.
spdif/optical are the one and same..optical can go up to 96khz i beleive...while analogue has a lower limit? i'll check and see..... but basically, they all use the same "codec". anyway, either format can deliver mono all the way up to 7.1....not too sure on the 7.1 ....but i know that 6.1 for sure.
the limitations on getting the 5.1 to your dream system work like this.....no current games offers dolbydigital 5.1......eax and whatever are similar, but differing ways to encode the DOLBYSURROUND mix. kinda like thx, dts, and DD.
so...dolby surround, albeit 5.1....is not 5.1. there are no channel-specific sounds....you won't hear those footsteps behind coming from JUST THE RIGHT REAR....you'll hear it on the right front as well. dolby digital, however, does offer this difference. and it makes a difference. but here's the kicker....you HARDWARE has to be able to take that dolbysurround and get it into DIGITAL to send it through spdif...and becomes 4.1 by the time you get it to your dream system. Unless, of course, you have hardware like the audigy2 that has a built-in doblydigital encoder....
so...farcry...dolby digital. hopefully your card has an OPTICAL out that offers DOLBY PASSTHROUGH so that your dreamsystem gets a signal it understands. in order for you to get the surround on your system, the dream system has to do the decoding, not your soundcard. and that is where the gigabyte hardware fails....no passthrough. although there is spdif output...you only get stereo. btw...the codec on my board offers 5.1 spdif out...but the included pci panel connector does not...
i can't really comment on hl2 and doom3...they are not out yet, but yes, unless your card will encode the EAX into dolbydigital or dts, you WILL NOT GET TURE 5.1...of course, you could always use the stereo input and have the dreamsytem decode it to SIMULATED 5.1....and that sytem does not a bad job.
in regard to the demo i saw.. it was a Dolby Digital demo direct from Dolby(whoever they are)...showcasing the difference between dolby surround and dolbydigital.

[Aedan]

Originally Posted by cadaveca

ahh.... then you are not getting dolbydigital 5.1....you are getting dolbysurround 5.1....
i thought that there was no difference, but i got an awesome demo @ the hometheater place that I normally shop at, and boy, does the spatialization effects ever differ.

There is no Dolby Surround 5.1 standard. Dolby Surround (and Dolby Pro Logic) is the older analog matrix surround standard that provided 4 channel surround. This works by doing some tricks with the stereo signal to multiplex a single rear channel and a single center channel on top of the stereo signal. Soundstorm is capable of doing this for receivers that can only handle older surround encoding. As there is only a single rear channel, sound positioning is much poorer with Dolby Surround than with Dolby Digital (AC3). As the matrix processing is a bit 'leaky' there's also some audio steering going on to try to attach sounds to particular channels. This further weakens the sound positioning, and makes for a less immersive experience. If you're using Dolby Surround, most receivers will indicate they're picking up a PCM bitstream, and then processing it with Pro Logic or Pro Logic II.

My receiver indicates that it's picking up an AC3 encoded bitstream. That on it's own indicates that the receiver is getting all 5.1 channels. AC3 is a fairly complex protocol that does some compression in order to fit the audio into the bandwidth of the bitstream available. Hence, ALL AC3 encoders have to do processing, if only to manipulate the audio into an AC3 bitstream.

If you haven't told Soundstorm to encode AC3, then you may well find that your receiver is running in Dolby Surround mode instead. This sends the Dolby Surround encoded data over two channel PCM information via SPDIF.

As far as I'm aware, Soundstorm is the only sound solution for PCs that's capable of encoding Dolby Digital.

[Aedan]

The SPDIF format is designed to run up to 96KHz sample rate in stereo with 24bit words. There is NO difference between the coax and optical, other than the fact that one is photons and one is electrons. The optical version works by pushing the SPDIF signal into an LED. Running flat out, the SPDIF format has a maximum bandwidth of 3.1MHz.

Dolby Digital (AC3) is an extra protocol (or CODEC) that can run on top of SPDIF that uses compression to fit all 5.1 channels into the space available.

EAX is a Creative standard for handling things like reverb, occlusion and other 'environmental' effects. This allows a programmer to hand EAX a normal sound, and have EAX alter the sound to fit with the supposed enviroment that the sound should have been in. For example, a game has the sound of gunfire in it. This sound is recorded 'plain'. You, the player, are in a ship, and open fire. The game then hands EAX the plain sound, and informs EAX of the type of enviroment. EAX then adds the reverb etc to make the sound sound like it was in the ship.

THX is a certification for sound reproduction quality. It is not tied into any particular encoding standard. As long as the sound is reproduced very well, the THX certification can be awarded. It does not concern itself with how the data gets from A to B, nor what kind of CODEC was used, or the type of connection between the equipment.

DTS is a competing encoding standard to Dolby Digital. It also provides a compression system to fit 5.1 channels into the bandwidth offered by SPDIF.

Dolby Digital EX is the extended version of Dolby Digital that uses further compression to fit up to 7.1 channels in the bandwidth offered by SPDIF.

Right, that out the way! nVidia's Soundstorm is the only system that I'm aware of that can ENCODE Dolby Digital, and fit those 5.1 channels of sound into a real AC3 bitstream. All other solutions that offer SPDIF (Optical or Coax) either send just the stereo information, or provide Dolby Surround encoding, which is far inferior to Dolby Digital.

Rumour has it that Realtek have implemented a solution that uses the CPU to do the Dolby Digital encoding, and offered it as an addon to their AC97 CODECs. However, there are licenses fees involved in producing a Dolby Digital encoder, so I suspect that few people have taken them up on that offer. Incidently, this is one of the reasons why MCP-T nForce2 boards cost more than MCP nForce 2 boards. Each MCP-T chip requires payment of the Dolby Digital encoder royalties to Dolby!

[stigweed]

One of the reviews for the Terratec Aureaon 5.1 Sky (the higher-end card than the 5.1 Fun) said it did Dolby Digital AC3 encoding. But that's the only mention, its not in the official specs and I can't afford one really.
http://www.biosmagazine.co.uk/article.php?id=245
I don't know if they're just assuming that because it's optical it has AC3.


What is ment by passthrough? Is that when the card just outputs a signal generated by software and leaves it in its current format? If this is disabled/unavailible, does that means that the card recieves the sound from it's driver and attempts to encode it for output (at a lower spec)?

EDit: what do you reckon to this:
http://cgi.ebay.co.uk/ws/eBayISAPI.d...ayphotohosting
Trust brand , description says Doly Digital 5.1 (AC3) PCI Sound Card. Google search for the item confirms "Dolby Digital" spec. Confusion thickens...

[Aedan]

Passthrough allows a program to pass an already encoded AC3 stream out of the SPDIF port. For example, a DVD player can pass the already encoded AC3 stream from the DVD to the receiver.

[stigweed]

From a review of the Trust 514DX:
"There was no distortion from the S/PDIF signal from a CD-ROM drive. However, stereo is the best you can get with the optical output, unless you have a separate Dolby Digital Surround Sound decoder. When using the separate Sony STRDE485 Decoder with the optical out, the 5.1 Digital capabilities could be seen - and the quality was ideal for gameplay and DVDs."

I take it this is likely to be on the passthrough?

[Aedan]

With Dolby Digital there's two items... First is the Decoder, that can take a Dolby Digital stream and decode it into the 5.1 channels of sound. Secondly there's the Encoder that can take 5.1 channels of sound and turn it into a Dolby Digital stream.

The Trust card appears to be based on a CMI8738 chip, which can decode Dolby Digital (with help from software). CMI make no claims to be able to do Dolby Digital encoding, so I suspect that it can't encode, but can pass through already encoded material.

Edit: Terratec make no claims for Dolby Digital encoding, so I presume it's just passthrough.

[Aedan]

Originally Posted by stigweed

From a review of the Trust 514DX:
"There was no distortion from the S/PDIF signal from a CD-ROM drive. However, stereo is the best you can get with the optical output, unless you have a separate Dolby Digital Surround Sound decoder. When using the separate Sony STRDE485 Decoder with the optical out, the 5.1 Digital capabilities could be seen - and the quality was ideal for gameplay and DVDs."

I take it this is likely to be on the passthrough?

To be honest, I dunno. Trust themselves stop short of claiming anything other than 'Dolby Digital'. CMedia, the people behind the chip driving the Trust card make no claims about Dolby Digital Encoding either.

Edit: Oh yes they do, but not on the products datasheet! The CMI8738's driver looks like it can encode Dolby Digital, as long as you don't mind the CPU doing the work.

[Aedan]

That means that any product with SPDIF and a CMI8738 might be able to do Dolby Digital encoding, as long as the right driver is present.