Problem with SPDIF input

[shaboodles]

I have been doing a lot of looking around on this topic but never found the answers I am looking for so I am going to explain my issue and hopefully someone on here can help me. I just bought this adapter http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=200290666672 to hook my xbox 360 and verizon HD box up to through both SPDIF ports. The problem I am having is that I am not getting sound from it.
By shaboodles at 2009-01-07 as you can see in this picture the realtek monitor is picking up the signal from the input.
By shaboodles at 2009-01-07 but in this menu i can not adjust the volume of the input for recording or playback (Im not sure if this really means anything)
My motherboard is a Gigbyte GA-MA770-DS3P. I have Logitech 5.1 speakers hooked up to the analog green, orange, and black outputs. So my guess is that the motherboard can not decode the SPDIF input to output through those ports. The motherboard does have SPDIF outputs so would I need to use those in order to get sound from the SPDIF inputs? If so that would mean that I would have to get a new set of 5.1 speakers that have SPDIF inputs.
Any feedback would be greatly appreciated. Thank you.

[Nelson37]

The lack of volume control is standard and is supposed to happen.

I would try AC3Filter to see if that will give you a real-time conversion. Many sound cards have spdif-passthru as the only option.

[shaboodles]

Nelson37, thanks for your reply. i actually do have ac3filter and other filters since I like to watch movies on my pc as well. I had forgotten to mention this so i apologize. But i found a technique of using the program "graphedit" to make a filter looking like this

By shaboodles at 2009-01-07
I actually got sound through but there was lots of static and choppiness to it. But when I set my xbox to output stereo I get good sound but it is delayed. I tried changing some of the settings around in Ac3filter but no cigar. I guess the only true way for this to work is to use the SPDIF outputs on the motherboard. But please feel free to let out any other ideas you may have. thank you very much.

[Nelson37]

I can tell you that my X-Fi card can do it, but I think it has an on-board decoder. Sounds like you're almost working, but in software only.

You could try playing an audio-only AC3 file using the same method, it should play a little better with the reduced CPU load of no video. Also perhaps try a lo-bitrate sound file, for the same reasons.

Do you get the same results using different players? At a minimum, there should be a noticeable affect on the sound. VLC versus PowerDVD, for instance.

Have you tested both sources, and can you test both into a standard amp to verify correct output?

Can you test the Coax input on the motherboard, if present? With either source?

A straight pass-thru to a secondary Dolby decoder should work.

I have not used the onboard Realtek hardware in this way, but have read a LOT of posts about sub-standard sound quality with this hardware. I HAVE experienced brief, occassional static and "pops" with other substandard hardware. Sounds like yours are more frequent and regular.

[shaboodles]

I tested it on my family room home theater system and got good results. The sound was clear and right on queue with the video. i set the option to pass through the SPDIF-in to the SPDIF-out in realtek and that seems to be the only legit way to get this working however, the current sound system I have for my computer does not have any SPDIF inputs so its either a new sound card or sound system. But before i spend more money Ill look into your ideas thank you so much for your help.

[shaboodles]

oh and i forgot to mention that i have tested both sources and i got the same results with the static and choppiness.

[dLee]

According to the Gigabyte spec sheet, the onboard audio is the Realtek ALC888 codec.

http://www.gigabyte.com.tw/Products/Motherboard/Products_Spec.aspx?ProductID=2939


According to the Realtek spec sheet for ALC888:

"The ALC888 series are high-performance 7.1+2 Channel High Definition Audio Codecs providing ten DAC channels that simultaneously support 7.1 sound playback, plus 2 channels of independent stereo sound output (multiple streaming) through the front panel stereo outputs."

http://www.realtek.com.tw/products/productsView.aspx?Langid=1&PFid=28&Level=5&Conn=4&ProdID=135

So it seems that when using an SPDIF input, it will output a stereo downmix through the front panel output only (in addition to the 7.1 passthru via the SPDIF out).

The rule with Realtek is that you should download the drivers from the realtek.com.tw site and install those - not the ones that came with your MB or computer - although I doubt that it will achieve the result that you're looking for.

A receiver or speaker system with SPDIF inputs and decoding will be required.

[shaboodles]

dLee, thanks for your feedback. I did decide to purchase a sound card with SPDIF inputs and onboard decoding since i found it cheaper than buying a whole new sound system. So hopefully this works, if not, then i guess it is not meant to be. Thanks again i appreciate everyone for giving me their ideas.

[dadudster]

Ok, so I have been looking into the problem related to AC3 streams not playing through the SPDIF input on the Realtek ALC888 chip. I am fairly positive that I now know the exact problem as to why we are not getting the audio stream, and unfortunately, the news is not good.

I downloaded the datasheet for the ALC888 chip and have been looking at how it handles the signal that comes in through SPDIF.
The chip IS capable of recognizing AC3 streams that are passed into it. However, most AC3 streams that are passed through SPDIF are copyright protected. This copyright protection is specified simply by a bit that is provided in the PCM stream that is wrapping the AC3 packets. The bit is also verified using a cyclical redundancy check (meaning a hardware device that can flip this bit is not easily obtainable).

Now, like I said, the ALC888 chip will recognize if a stream is AC3, but it will also read the copyright protection bit.
You can verify this on your own by simply plugging a device that is outputting Dolby Digital directly into the SPDIF input and goto the Realtek HD Audio Manager ---> Digital Input tab ---> Digital Audio Input tab. You will see under Sample Rate: "AC3 48Khz". You will also see under Copyright Protection: "No Copy".

And now we have arrived at the crux of the matter. It is not a lack of technical ability that is preventing us from using our PCs as a receiver. It is POLITICS!

My belief is that when the copyright protection is in "No Copy" mode, the Realtek chip will either:
1. Not pass the signal, or
2. Pass the signal, but not indicate to directshow that the signal being passed is AC3. Instead it just defines the signal as a 2 channel PCM signal.

My guess is that it is the 2nd thing, because AC3Filter still recognizes that it is receiving some sort of signal, but it is handling it as if it was 2 channel PCM instead of an AC3 packet wrapped in a PCM stream.

So in order to fix this, I think, one of the following needs to happen:
1. Realtek has to change its policy and allow copyright protected AC3 signals to be specified in directshow (not likely to happen for legal reasons I think).
2. Someone needs to modify the ALC888 codec to force it to specify a stream coming into SPDIF as being an AC3 signal (this will only work if your signal is, in fact, AC3).
3. Create a modified AC3 Filter that will just ASSUME the signal being passed to it is an AC3 signal wrapped in a PCM stream (probably the most doable option, but I don't know if it will actually work).
4. Add support for hardware decoding of AC3 streams to the d2audio chip and just pass the stream straight from the Realtek chip to the d2audio chip (the best solution overall because it would allow ALL AC3 signals regardless of source to be hardware decoded, but I'm not sure if it is possible or something d2audio is planning on doing).

Regardless, this is what I have found out in my day of research.

In case you want to look further into what I have discovered here are some links:
The ALC888 Datasheet
A patent by Hughes Electronics which provides some great info on how AC3 packets are wrapped in a PCM stream

[INFRATOM]

To get sound from a source you have to go to the properties of the volume control and select record or playback in this case is record then it shows you the controls, select digital in or whatever your source is then you can hear from the source. When you are recording I suggest you mute the other ones specially mic if you have one connected.
If you want to buy a sound card look into ASUS they have nice ones. Make sure you don't buy Auzentech the driver comes with spyware and a license manager if you remove it software gets disabled through license manager and you have to format your windows to recognize it again.

[Nelson37]

The signal passed over an SPDIF is a two-channel PCM stream, regardless of what it carries. It is sort of like a ZIP file, it has to be decompressed or decoded back to its original form. 48k, stereo, no volume control.

Most soundcards with SPDIF use it only as a pass-thru, with NO decoding capability. A very few sound cards can record the raw file accurately enough for later software processing to create a true 5.1 ac-3 file. Many can decode the SPDIF input to 2-channel stereo, with varying degrees of success.

As for 5.1 SPDIF in to ANALOG 5.1 out, you need an on-board Dolby decoder. I know the X-fi will output to all five speakers with this setup and am reasonably certain it was identical to the original surround, but I did not test this heavily. Research showed this was a fairly rare capability. My interest was in recording the SPDIF input for video captures.

The fact that you did get some sound from the PC speakers will using SPDIF-in with a surround source shows that decoding was indeed happening, but possibly only thru software. Can you verify whether this was a 2-channel downmix? You might be able to improve performance in this area, but just switching the source output to 2-channel PCM would be a better way to go.

[dadudster]

I have created a new thread on the AVS Forum to compile all of my knowledge about SPDIF related issues.
http://www.avsforum.com/avs-vb/showthread.php?p=15846010#post15846010

It provides a really detailed compiling of everything I have discovered about this issue, and lists the limitations in detail.

Lets move all further discussion related to this issue to that thread.

Also, please circulate the thread. I would like it to become a sticky in that forum subsection (so that people wont waste the hours I have wasted on this issue).