View Full Version : Broke AC3 passthru via SPDIF :(

4th February 2006, 23:49
I have a M-Audio Revolution 7.1 soundcard and for ages I have had no problem sending AC3 passthru to the SPDIF output (AC3 reciever lights up blue meaning it is getting 5.1 etc). Now all I get for some reason is PCM via SPDIF. It's not the receiver as it plays back RAW AC3 fine from a DVD player.

I have tried the following.

Uninstalling/reinstalling the audio drivers.
Various flavors of AC3Filter (SPDIF enabled, disabled, dshow, waveout, AC3 passthru boxes checked etc)
Intervideo's AC3 decoder (SPDIF ticked. Nothing comes out the other end).
Cyberlinks (No option for SPDIF output is now shown where before it used to. As if it cannot recognise SPDIF as an option).
Unregistering and re-registering filters.
Various flavors of ffdshow with SPIF selected for AC3

Short of wiping XP SP2 I have tried everything.

Before I go that route is ther anything else I can try? Is there any way to repair the registry perhaps to correctly identify and route AC3 filters?

I am wondering if something is seriously screwed up in the registry.

BTW I did have Nero installed and it stole the audio rendering. But even if I went into that filter and tried to force the SPDIF radio button on the player would look up (Zoom Player BTW). Also Media Player Classic will not play any AC3 AVI's when SPDIF output is selected in options.

This is very frustrating :/

5th February 2006, 00:16
Mostly it's a sync problem between the receiver by unsupported sampling rate with driver or codec.

Try any DS enabled player(i.e. MPC) to use the FFDShow ds filter.
Be sure to check the resample DSP and 'resample to 48k if below 48k' inside.
Also check the codec settings to enable the dts/ac3 decoding and output setting to ac3(640k) to enable the dynamic ac3 encode & spdif passthrough.
Various flavors of ffdshow with SPIF selected for AC3
It's for PURE spdif passthrough which bypasses even the ffdshow internal codec & DSPs.
It will be useful for originally 48K raw streams.
Set it to correct decoder(s) to use the resampling DSP...

similar issue but on capturing.

5th February 2006, 02:28
Tried the above. It makes little difference. I cannot even get ffdshow to be the default audio decoder anymore. It either defaults to 'AC3 Audio Decoder' which is greyed out in MPC during playback and I get no sound (And nothing not even PCM 44.1Khz on the reciever). Or if I try to force it to use ffdshow it ignores it and uses Intervideo's AC3 decoder to SPDIF and I get 44.1Khz of PCM static.

EDIT: I just used Radlight's filter priority prog to set ffdshow to highest and it used ffdshow for audio decoding in MPC. But I still had the same problem. PCM 44.1Khz only no matter what I forced to 48Khz AC3 SPDIF out in ffdshows settings. I am going to have to wipe XP I think and start again.

5th February 2006, 03:59
With MPC also, you can set the priority(MERIT) of the (AC3 or other format) decoder filter selection : View->Options->Filters->Overrides
Place the FFDShow at the top of the lines(up/down) and check the 'prefer' option for the merit.
You may also have to set the FFDShow's own audio filter setting menu( 'program files>>') to enable the ac3 decoding.
If any codec(decoder) hinders you, you can also 'block' it permenantly for MPC.

Based on your last statement, I am sure it's the sampling rate(signal sync) problem.

5th February 2006, 11:37
Yup. Tried all the above. Something either in the registry or a borked file or ini file is telling everything that tries to output to the soundcard's SPDIF that it can only send 44.1Khz PCM even though the soundcards mixer is set to 48Khz digital out (This is the normal setting for AC3 passthru. It has Stereo, a number of multiple speaker out selections and digital).

The system is long overdue for a wipe anyhow. Going to get another hard drive now so I can do a fresh install and still get access to any files that I need from this drive.

5th February 2006, 17:33
The way the system mixer treats the spdif passthrough are different by the drivers of the cards.(I am a soundstorm user currently)
Normally the s/w player's spdif passthrough bypasses the system mixer processing. But the setting in the system mixer for the driver is a different story.
Setting the system mixer with a normal analog speaker set(5.1/2.0) would be ideal for the FFDSHow to work(ac3 encoding & spdif passthrough) properly without any interference. Also check if the spdif-in->spdif-out bypass is enabled if the driver supports it(disable it).

The fastest way to check if your soundcard can spdif-passthrough the 48k stream at all, would be using the originally 48k encoded ac3(from dvd tracks, web or foobar2k v0.83 transcoding with upsampling) either relying on FFDShow pure spdif passthrough or system mixer setting.

The normal route is:
*.ac3(44k)->FFDShow Decode-> FFD upsample(48k)->FFD ac3out(passthrough request to audio driver)->CODEC spdif transmitter->receiver reception-> receiver decoding.

I think there's a problem in the step : FFD ac3out(passthrough request to audio driver), maybe by the mixer spdif passthrough setting.

6th February 2006, 09:36
Found the offending software that was killing AC3 passthru. After a fresh install of XP everything was working until I installed my new Logitech Quickcam Pro 5000 software. BANG! No AC3 passthru anymore. System Restore to point prior to install and it's working again. Installed software again and it breaks again. Try uninstalling software and not doing System Restore and it's still broken. Do a System Restore and install JUST the webcam drivers manually (Audio and Video drivers) and AC3 passthru works fine.

The software installs a number of processes. Killing any of those processes has no effect on AC3 passthru though. My guess is it's something to do with another portion of the software called 'Automatic Echo Cancellation' which is part of the Logitech install. Though I am not 100% sure.


6th February 2006, 15:31
Maybe some part of the application (installation) is touching the audio device address related to the spdif-out. Anyway it's a good news.

Our common issue now would be if the M-Audio Revolution 7.1's mixer setting to digital out adjustable to sampling rate of the source(48k/44k).
In other words, do you still need the FFDShow's 48k dynamic resampling?

7th February 2006, 15:21
Only for multi channel AAC etc which I have set in the default settings file for when it detects 6 channels.

Not sure how to get around the Logitech problem. I will have to email them.

7th February 2006, 19:43
I think so. Anyway, oh my fingers!;)

20th February 2006, 23:32
After much fapping about I found out what is causing the problem.

Audio Echo Cancellation (AEC).

It's part of the Quickcam installation. I ended up deleting the InstAec.exe file and using one of the other driver exe files and renaming it to InstAec.exe so I could at least install everything else.

I have passed the info on to Logitech but I doubt they will do squat about it. The neasty thing is if you install this exe then unless you have a system restore point to go back to you are frakked. Uninstalling the software and drivers does not remove whatever that particular component does (Probably a registry entry or file that it replaces).

20th February 2006, 23:38
Mostly nobody knows/sees better than the the owner...
Only for multi channel AAC etc which I have set in the default settings file for when it detects 6 channels.
Was the AAC etc 48k or not?
A similar case with M-Audio Sonica Usb sound card (http://forum.doom9.org/showthread.php?t=91848). Your case seems to be caused by complex reasons.:cool:

1+1=1... hmm...

27th February 2006, 22:49
Yepp, what should one say :mad: I have exactly the same problem--no S/PDIF passthrough availalbe any more. I also have the Logitech Webcam 5000. My soundcard is a Terratec Sixpack 5.1+ (a Crystal CS4630 DSP).

I noticed the issue is also mentioned in the Logitech user forums. See if new drivers will arrive :confused:

27th February 2006, 23:00
Ohhh. I actually got it to work. In Device Manager->Sound, video, and game controllers, I disabled the Logitech Microphone (Pro 5000) device. Rebooted, and ... S/PDIF is again selectable :)

Not a solution, but a workaround :-\