Impossible to get Digital 5.1 from AC3 Source?

[Codesmith]

I used to have my SB Live 5.1 connected to an old non-digital reciever via RCA cables. When I watched a DVD, AC3 DivX, or played an AC3 test file, all 5 channels played from their correct speaker.

Then I bought and new Pioneer VSX-D912K reciever which supports optical and coax digital inputs.

I connect my SB Live 5.1 to the reciever via coax, set my speaker mode to SPDIF, uncheck AC3 decode and use Power DVD (also set to SPDIF) to play a DVD with THX audio Tests. The reciever indicates a Dolby Digital signal and all 5 channels are comming out of the correct speakers. Then I try a DTS DVD and rejoiced.

Finally I set AC3 Filter to SPDIF, and play my trusy old ac3 test file. The 3 front channels work as expected but I hear "rear left" and "rear right" comming out of both back channels! I check my reciever and it indicates the signal to be Dolby ProLogic II (4.1 with center/rear) rather than Dolby Digital.

I fire up my 2nd PC and connect its CMedia card to my reciever via an optical cable. SPDIF passthrough works great with DVDs, but no joy with AC3 files or AC3 encoded DivX movies. Still 4.1 rather than 5.1.

I even try Media Player Classic (set to SPDIF) and PowerDVD to play the DivX/AC3 file. Still 4.1

Now my SB Live 5.1 can only encode into 4.1 in SPDIF mode, however its not supposed to be encoding anything, its supposed to send the unmodified audio bitstream to the reciever for decoding. However my CMEDIA can only encode into stero when in SPDIF mode, and I am definately getting 4 channels. So the AC3 filter is using SPDIF passthrough, but it is downmixing to ProLogic II in the process.

Summary

AC3 from any source + sound card decodes = real 5.1
AC3 from DVD + reciever decodes = real 5.1
AC3 from non DVD source + reciever decodes = 4.1 (one rear channel)


I am completely stumped on this one. If anyone knows of an alternative to AC3Filter or have full digital 5.1 working form a non DVD AC3 source.

Any help will be appreciated, even if its just to tell me of another forum where someone might be better able to help with this problem!

PS Are there any open source DVD players with working SPDIF pass through. Maybe if I could compare the code between that and AC3 Filter I can find the problem?

[KpeX]

Hi -

It's definitely not an AC3filter code problem, nearly everyone uses Ac3filter for spdif pass through. I'd recommend going through the AC3 FAQ linked in my signature, just to make sure nothing basic is missing.

Check your AC3Filter settings as well, make sure it is set to S/PDIF.

AC3Filter cannot use SPDIF pass through and downmix to DPLII. DPLII is only in stereo streams. If you are using SPDIF the output will be DD5.1 if the source is DD5.1. hth,

[Codesmith]

I had to install ac3filter twice for some reason and the control to switch between waveout and directsound is broken, but none of that mattered. Nor did trying every available driver version.

What I have is a "magic" AC3 test file!

In 5.1 mode its a 5.1 bitstream, using SPDIF its suddenly a 4.1 bitstream.

My guess it that there are two audio tracks in the same file? Or maybe it has 6 channels, but is incorrectly encoded. Which my sound ignoring the rear center and my receiver ignoring the left and right surround?

I can play other AC3 and avi test files fine. Each speaker is outputing the correct channel and my receiver shows Dolby Digital or Dolby Digital Ex instead of Prologic!

I downloaded this test file off of someones website because each speaker annouced its channel. The other ones play each speaker without announcing, or visually show which channel is being used.

In any case I am very happy. :)

Now I just need a set of Kilpsh 5.1 speakers :)