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Discussion Starter · #1 ·
I've been having weird issues with audio in Ubuntu 9.10, particularly in XBMC. I have an Asus M3N78-VM motherboard, and originally, audio in XBMC only worked if the output was set to "Analog" (this despite the audio actually going through the HDMI connection). Removing pulseaudio (cursed be its name) per tux99's standard advice and the procedure offered here fixed this issue and now the audio output options in XBMC seem to correspond with what my machine is actually doing.


It seems, though, that I've just opened up a whole different can of worms: the navigation sounds in XBMC no longer play, and videos with AC3 audio tracks only output rapidly pulsing static (2ch AAC audio tracks play just fine, though). This happens with the following XBMC audio output settings:

Audio outputDigital
Dolby Digital (AC3) capable receiver[x]
DTS capable receiver[ ]
Audio output devicehdmi
Passthrough output devicehdmi
Downmix multichannel audio to stereo[ ]

If I uncheck AC3-capable receiver and check "Downmix multichannel audio to stereo", videos with AC3 audio tracks work again, but obviously are only playing in stereo. The navigation sounds are still non-functional.


My machine is connected through HDMI to my TV (Panasonic TH-42PX80U) via a Monoprice 4x1 HDMI switch. The TV is connected to my receiver (Samsung HT-Z510T) via a Toslink cable. The TV's manual is confusing in that, on pg. 38, it claims "When audio from other equipment connected to this unit via HDMI is output using 'DIGITAL AUDIO OUT' of this unit, the system switches to 2CH audio." However, it then says on pg. 43, "You can enjoy your home theater by connecting a Dolby Digital (5.1 channel) decoder and 'Multi Channel' amplifier to the DIGITAL AUDIO OUT terminals."


I don't have the static problem when playing back DVDs on my Xbox 360 (which is connected via the same arrangement, although playback is still only in stereo), so I'm hesitant to blame the connection chain for this one. Does anyone have any ideas on what could be wrong? Is there any way I could possibly get 5.1 sound from my HTPC short of throwing out the receiver and HDMI switch in favor of a receiver with HDMI inputs?
 

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To me it sounds like it's a problem with your soundchain, but I might quite possibly be wrong. A cheaper solution than throwing away the receiver and get a new one with hdmi (seems a bit costly and radical to me if the receiver is working fine), would be to buy a cheap PCI soundcard with digital out and use that to send the sound directly to the receiver.
 

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Discussion Starter · #3 ·
tux99, I agree that getting a new receiver is a pretty radical solution, but I wanted to provide some bounds on the solutions offered



I was thinking perhaps the Monoprice 4x1 HDMI + SPDIF switch (has coax, optical digital outputs and stereo analog output) might work, as it would allow me to bypass whatever weirdness the TV is doing with digital audio while still being able to switch between digital audio sources. I have no idea if this would actually work like I think it works, though, and I can't link to it right now because Monoprice's site is down. If that's not a solution, I suppose a cheap sound card would be necessary, as it looks like ALSA still cannot recognize the optical out port on my particular motherboard (going by several threads here and elsewhere detailing this problem).
 

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If your receiver is capable of optical SPDIF input, then I'd find a well-supported, inexpensive sound card with optical SPDIF output and use that. The only real advantage with HDMI audio (other than having one less cable) is 7.1 which currently isn't supported in linux. I've been using optical SPDIF pass-through to my receiver that can decode DD and DTS ( Logitech Z-5500 ) for years now, and it works beautifully even with BluRay rips (the 7.1 HD audio tracks have a "core" 5.1 DD or DTS track for compatibility). Granted, my sound card is a bit overkill because it has hardware DD and DTS encoders that I use in Windows because I still have to boot to it for a few reasons, e.g. Netflix. I'm sorry, but $8/mo. is a sweet deal for the amount of content they have available to watch instantly. I'm gonna see if it works from a VM when I get off my lazy ass and build my app server, but I really don't expect it to.
 

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Discussion Starter · #5 ·
mythmaster, I agree that an inexpensive sound card with SPDIF and support under Linux is a solution. However, it leaves my other devices (set-top box, Xbox 360) out in the cold unless I want to unplug the optical cable and replug it every time that I want to switch devices.
 

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Quote:
Originally Posted by indubitable /forum/post/18266017


I was thinking perhaps the Monoprice 4x1 HDMI + SPDIF switch (has coax, optical digital outputs and stereo analog output) might work, as it would allow me to bypass whatever weirdness the TV is doing with digital audio while still being able to switch between digital audio sources.

That could work, but I obviously have no experience with that switch so can't tell for sure. Might be worth a try if it's inexpensive (or if you can return it if it doesn't work as expected).
 

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Quote:
Originally Posted by indubitable /forum/post/18266723


mythmaster, I agree that an inexpensive sound card with SPDIF and support under Linux is a solution. However, it leaves my other devices (set-top box, Xbox 360) out in the cold unless I want to unplug the optical cable and replug it every time that I want to switch devices.

That or get a TOS switch, they are not too expensive.

http://www.compbargains.com/_e/Syste...tor_Switch.htm


How many TOS ports does your receiver have? I'm guessing one.
 

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Discussion Starter · #8 ·
Hmmm... this is getting interesting. From another thread on the forum , it appears that the switch in question wouldn't help. It looks like a Catch-22 situation: there will only be DD5.1 sent across the HDMI path if the television says it supports 5.1 during the HDMI handshake, but the only reason that you'd use a device like this is if your TV didn't support 5.1 sound. So it looks like my other devices (e.g., Xbox 360) do a negotiation during the HDMI handshake and then silently downgrade to 2ch PCM before sending content over the HDMI link.


On the other hand, someone in that thread posits that you might still be able to achieve 5.1 output if your source (the HTPC, here) overwrites the EDID handshake and decides to output 5.1 anyway. Could this be what my machine is doing??? It would certainly explain the garbage audio when I tell XBMC that DD5.1 is supported. Maybe Linux just doesn't support this autonegotiation feature and all HDMI output is manually set on the Linux side? Are there debug options somewhere that would let me see what's going on at the protocol level of the HDMI link?
 

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Quote:
Originally Posted by indubitable /forum/post/18266723


mythmaster, I agree that an inexpensive sound card with SPDIF and support under Linux is a solution. However, it leaves my other devices (set-top box, Xbox 360) out in the cold unless I want to unplug the optical cable and replug it every time that I want to switch devices.

Your receiver won't allow you to switch sources? Maybe you do need a new receiver.
 
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