I had the same problems as this post, and I solved them the same way.
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http://mysettopbox.tv/phpBB2/viewtopic. ... hlight=ac3
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But, I have not been able to get rid of my HDTV digital sound problems. I get good sound though the line out jack, but as soon as I switch over to digital I get no sound except what I can only describe as a helicopter.

Now I had some old SDTV recordings from before I upgraded to R5A12 and an HD-3000. They play perfectly throught the digital out. From what I understand these would use PCM. I also have learned that HDTV uses AC3. This seems to be where my problem is.

Again if I use Xine and set it for Pass Through (and use a DVD with AC3) I get perfect sound. So is this a problem with the mythtv playback, or is the digital audio of HDTV different somehow

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FRONTEND 1 - R5A16, Athlon 3000+, NVidia Motherboard, SB live, GeForce 5200, AA 9A60
FRONTEND 2 - R5A16, Athlon 2500+, Nvidia Motherboard, SB Live, GeForce 440MX, TV-OUT
BACKEND - R5A16, Althon 1700+, Nvidia MB, 2- HD3000's, 450GB LVM partition

Ok This is stupid. I was searching the gossamer-threads and found something about disabling AC passthrugh in the mythtv general menu. It worked.

So now until I get rid of the old recording I need to toggle this on and off.. ARRRGGG.

This can't be right

_________________
FRONTEND 1 - R5A16, Athlon 3000+, NVidia Motherboard, SB live, GeForce 5200, AA 9A60
FRONTEND 2 - R5A16, Athlon 2500+, Nvidia Motherboard, SB Live, GeForce 440MX, TV-OUT
BACKEND - R5A16, Althon 1700+, Nvidia MB, 2- HD3000's, 450GB LVM partition

Ok, So I am Stupid. You don't need the AC3 passthough checked for PCM.

Well, I guess I didn't need help after all. All I can say is I hope my rambling help someone else.

Problem solved. Well, at least until they fix this bug.

_________________
FRONTEND 1 - R5A16, Athlon 3000+, NVidia Motherboard, SB live, GeForce 5200, AA 9A60
FRONTEND 2 - R5A16, Athlon 2500+, Nvidia Motherboard, SB Live, GeForce 440MX, TV-OUT
BACKEND - R5A16, Althon 1700+, Nvidia MB, 2- HD3000's, 450GB LVM partition

Not all is solved, I looked on my stereo and when I am playing a AC3 dvd the dolby digital light comes on and my little channel map shows all five channels lit up. When I try to play HDTV content, I get a dgital light, but no dolby digital light, and only the left and right speakers light up.

My guess is that mythtv is converting the AC3 to 2 channel PCM What the Pass AC3 checkbox does is turn off the AC3 to PCM conversion and directly pass the AC3 to the digital out.



Long story short. AC3 through Mythtv playback still doesnt't work.

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FRONTEND 1 - R5A16, Athlon 3000+, NVidia Motherboard, SB live, GeForce 5200, AA 9A60
FRONTEND 2 - R5A16, Athlon 2500+, Nvidia Motherboard, SB Live, GeForce 440MX, TV-OUT
BACKEND - R5A16, Althon 1700+, Nvidia MB, 2- HD3000's, 450GB LVM partition

the program you were trying to watch is really D digital right?

I would have to assume so because it has the PBS digital thingy in the beginning and it is 1080i. Anyway from what I have gleamed off the web, (I could be entirely wrong) I thought AC3 was the way audio was encoded, just like older low res TV shows are upconverted to 720p or 1080i for teansmission (except fox or stations that choose to split thier channel into 4 or 5 streams.

_________________
FRONTEND 1 - R5A16, Athlon 3000+, NVidia Motherboard, SB live, GeForce 5200, AA 9A60
FRONTEND 2 - R5A16, Athlon 2500+, Nvidia Motherboard, SB Live, GeForce 440MX, TV-OUT
BACKEND - R5A16, Althon 1700+, Nvidia MB, 2- HD3000's, 450GB LVM partition

I think some programs even tho are form HD don't actually transmit in 5.1 surround. I noticed this because sometimes my receiver will have the rear speakers lit up and some other times it won't. I still hear sound from the back speakers but I think it might just be in the old 4.1 or dolby surround instead of dolby digital. that's what I think anyway.

welp, having to switch back to SB Live, I noticed the same problem here. So far I found this link. http://www.linuxlogin.com/linux/emu10k1.php but I've not try it yet. I think it might be a MythTV thing tho...dunno.

this is what I did for AC3 output with SB Live + spdif daughterboard

Setup -> General -> Audio output device = ALSA:iec958
check enable AC3 to SPDIF passthrough

and that get me AC3 for HDTV

for MythVideo, I added
-ao alsa:device=hw#0,0 -ac hwac3,
and that sees to enable AC3 for mplayers (I was able to test it out w/ my DVD rips.

Hope this helps.

Say Grooby,
are you finding that all the HDTV channels are in AC3, some channels, or just some programs. I copied what you did and it works, but I haven't seen my Dolby Digital light go yet and audio doesn't work at all if I check enable AC3 to SPDIF passthough. I've tried with about 10 different recorde programs and all my live stations. I can't believe LOST isn't in AC3.

On another note, I found out that SPDIF OUT 0 comes out of both the orange digital jack and the 40 pin header (pin 17 and a GND) of my Sound Blaster Live. I learned this after I made my own daughtercard of sorts and discovered that I was using SPDIF OUT 0 all along.

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FRONTEND 1 - R5A16, Athlon 3000+, NVidia Motherboard, SB live, GeForce 5200, AA 9A60
FRONTEND 2 - R5A16, Athlon 2500+, Nvidia Motherboard, SB Live, GeForce 440MX, TV-OUT
BACKEND - R5A16, Althon 1700+, Nvidia MB, 2- HD3000's, 450GB LVM partition

I know most of those shows at nite are AC3. I.e. CSI, Lost should be one of them, House,...etc. Have you try to play an AC3 video? (maybe rip a DVD with AC3 audio encoding and try to play back?) just to make sure the receiver is setup ok.

I just tried two videos, one had 2.1 (Dolby digital light came on and left right and rear(single) came on) The other had 5.1 (Dolby Digital light plus L-C-R LS, RS and LFE all came on) I know they were 5.1 and 2.1 because I used control-I in Xine.

Maybe I haven't hit upon an HDTV show with AC3 yet....

Maybe a better question to ask is can you leave AC3 to SPDIF passthough checked when you aren't watching AC3 enabled shows, or do you have to keep toggling the check box.

Thanks...

_________________
FRONTEND 1 - R5A16, Athlon 3000+, NVidia Motherboard, SB live, GeForce 5200, AA 9A60
FRONTEND 2 - R5A16, Athlon 2500+, Nvidia Motherboard, SB Live, GeForce 440MX, TV-OUT
BACKEND - R5A16, Althon 1700+, Nvidia MB, 2- HD3000's, 450GB LVM partition

I leave it checked and everything plays fine.

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