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5.1 sound gets lost from cable box???

399 Views 16 Replies 5 Participants Last post by  edraven
Does anyone else have this problem? I run S/PDIF (optical) into my motherboard (Abit NF7) from my HD cable box (Motorola) and the 5.1 sound gets lost. I can capture stereo sound and play that back through the on-board sound card, but if the sound comes from a HD signal all I get is static. I have tried sending the sound to the receiver as S/PDIF out and as analog out, but the same result. I have also tried to use my Revo 7.1 card but no luck. I know the 5.1 source is ok because it works to run directly from the cable box to the receiver, but what fun is that? Any ideas???

thanks as always,

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it doesn't work because that is an optical out on your Nf7-s and optical out on your cable box. you had it right with your 1st setup.

cable box to receiver

computer to receiver

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no, i think he does have an SPDIF input, because he says he can play stereo audio fine. Jakill, i'm having the exact same problem as you. I'm trying to run SPDIF (coax, not optical) into my Audigy's CD_DIGITAL input. stereo plays back fine, but i can't find anything to decode AC3. I've tried the kX drivers, which work nicely for other things but their AC3 decoder doesn't work for this. The only other thing i can think of is to route the sound to AC3filter, but I can't find a program that will do that. THe first thing i tried was WinAmp with the line-in plugin. That will play back the source fine, but it still doesn't allow any extra processing on the signal. I sent this email to the creator of that plugin asking about it:

I'm trying to decode an AC3 signal from the SPDIF

input on my sound card, and I think your plugin (in

conjunction with AC3filter) can do this. I've gotten

your plugin to play the source, and regular stereo

audio plays fine. With an AC3 signal, however, it

seems to just send it to DirectSound in the same way

and it never gets decoded. Is there a way, with your

plugin, to either make WinAmp think that it's playing

an AC3 file so it uses the WinAmpAC3 plugin to decode

it, or make DirectShow decode the AC3 signal itself?

I'm not sure if you'd be likely to know this, since I

don't think this was really the intended use of your

plugin, but I figured I'd ask.
here's the response i got:

You are right that this wasn't the intended!

But it's interesting none the less.

Tricking Winamp into thinking the linein signal is an AC3 file won't

work, as the input plugins are themselves responsible for opening and

reading the files (so I can't feed it the signal directly). What you

could try to do is store the recorded signal to a file (output to the

raw pcm format and give it the right extension) and play that file from

within another instance of Winamp. I think this should work in theory,

and I could modify my File Writer plugin if that's needed (it might


some changes in the file sharing settings). One way to check whether

this would be possible is to first store a (small) stream this way and

then try to play it afterwards (while it isn't being written to

anymore), if this works it should probably be possible to make this


in realtime.

Another option would be to use some kind of DSP plugin to decode the

signal (although this is tricky, as the output of the DSP plugin can

never be more than two times the size of the input, I could try to lift

that restriction a bit in this case though). I don't know what DSP

plugin you would need, but I know there should at least be a DSP plugin

that can use DirectSound effects, so it may be possible to use that

(perhaps the developer would be willing to adapt it to allow for this).

Then there is the option of using a different player, Foobar2000 might

be capable of what you want to do, but it would probably require some

new plugins. Winamp 3 would also be a possible candidate (although


have to find someone willing to make plugins for it), and perhaps there

are other players out there which would support things like this.

Last but not least you could try using Graphedit to construct a filter

manually. I haven't used this program often myself, but from what I've

seen it's pretty powerful, you can connect arbitrary DirectShow

components and as far as I can see it's also possible to input directly

from the soundcard with this. If you can't find it, it's at least

included in the DirectX SDK (downloadable from microsoft, probably from

msdn.microsoft.com). It's not the most user-friendly program, but it


probably do what you want. And if you need the decoded output in Winamp

again you could use Virtual Audio Cable, just let Graphedit output to

the VAC and use Winamp to input from the VAC again and you're all set.

If you don't need to do this in realtime the problem becomes much less

complex, but you probably figured that out already (assuming the AC3

stream can be read by a normal AC3 decoder), as you can then simply

store the recorded signal to a temporary file and then decode it.

I haven't had time to try everything in his email, but I'm gonna try some of it later. Hopefully this helps, as it'd be great to get this working.

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AC3 Filter should be able to decode it for you.
All I really need is to pass-through the digital sound from the NF7-s optical input to the optical output. It would be better if the pc was able to decode the 5.1 as this would allow PVR functionality etc. There must be a way to get this going. Good input so far...

oh, passthrough is easy. get the kX drivers and there should be an AC-3 passthrough option in the mixer. those drivers are great, but not ready for hardcore gamers yet (no EAX support).

DaveFi, I'm sure AC3filter could decode it, but I haven't figured out a way to get the signal into AC3filter yet. If you know of a program that can just play back inputs with DirectSound filters, that'd be great
I can't use the kX drivers (as far as I know) because I've got the Nvidia soundcard on my Abit NF7 motherboard. If I can't get it working through the on-board Nvidia, maybe I will just buy a better soundcard. Any suggestions for something with digital in/out, analog out, and good home theater driver support...?

Originally posted by jakiii
... from my HD cable box (Motorola) and the 5.1 sound gets lost.
This may be off topic, but if your box is a 6200, you can just send audio (and video) via firewire to your HTPC
i'll be getting a 6200 soon (this saturday) and I didn't think of that possibility, though it may be a good solution. I'd have to get a firewire card for my PC, but it may be my only option. Is there a program for PC that can play back the video and audio over firewire without recording it? I'd probably want to record some of it, but for everything else i'd just want to play back the audio through my speakers.


you can use videolan player to open the capture device driver (firewire card)
care to elaborate? that would be hardcore if that worked.


i just tried it with my sound card and it worked; don't have a firewire card to test it with. go into VLC and choose "File > Open Capture Device" or something similar and then next to the video devices click refresh and choose the firewire device. should work, i assume.
when I try to "configure" the video my machine reboots, any ideas?


would it be possible to take the firewire data and stream it over VGA to different displays

Ex: Cable box w/ firewire to Computer

Stream from Computer to different displays w/ VGA connections

My interests are in the HD channels.



I'll assume that the firmware version of the cable box will play a part in the success or failure.
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if you have a comcast box (DCT 6200 or 6208) you seem to need firmware version 7.10. I've heard about VLC crashing when you try to configure, so i'd just try to avoid that setting. it seems to work otherwise. and yes, you should be able to play it back on any display with VLC.

i haven't tried this personally yet, but hopefully i'll have the equipment soon so i can attempt it personally.. there's some good threads on it in the HDTV Recorders forum.
that 7.07 firmware has been haunting me for months:(


DVHS unit doesn't crash VLC for me.... need to read up on VLC now
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I think the issue is more the hacked "panasonic" driver used for the moto 6200 that makes it crash, not VLC having some problem.
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