LG TV + Digital Video + Analog Audio Not Working [SOLVED]

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LG TV + Digital Video + Analog Audio Not Working [SOLVED]

Postby Jorpho » Sun Nov 27, 2011 3:05 am UTC

So I was mucking about with my LG flatscreen TV today. There's a 3.5 mm jack on the back labelled "Audio In (RGB/DVI)". And indeed, when I'm using the VGA input port and plug an audio source into this jack, all is well.

The problem comes with HDMI. There are no DVI ports on the TV, per se, but it does have plugs for HDMI cables, so I use a DVI-to-HDMI adapter to plug in my computer's video card. If I have an audio source plugged into the "Audio In (RGB/DVI)" port and switch the TV to one of the HDMI inputs, the audio comes out of the TV speakers – but only as long as there's nothing plugged into the relevant HDMI input. As soon as I connect my computer, the audio shuts off!

The manual appears to imply that this should be possible.
hdmi_in.png

hdmi_in_2.png


The obvious simple solution here is to buy another video card with HDMI out, which I'm not really prepared to do. Alternatively, I'm told there are devices which can re-encode (?) analog audio and interlace it with a DVI signal, but those are apparently expensive.

Am I missing something here somehow? Is there perhaps a more specific variety of DVI-to-HDMI adapter I should be using? It's in the manual twice!
Last edited by Jorpho on Mon Nov 28, 2011 3:04 am UTC, edited 1 time in total.
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Re: LG TV + Digital Video + Analog Audio Not Working

Postby Dream » Sun Nov 27, 2011 2:46 pm UTC

Have you checked whether the audio is absent at the computer end, or the TV end? Link up the DVI->HDMI such that the audio isn't coming through, then connect an MP3 player instead of the computer and see if audio comes out of the TV. My guess is that it won't. I suspect the TV is prioritising the digital audio stream over the DVI connector, and your soundcard either does not, or isn't set to send audio via that connection. The TV manual may simply have omitted that it defaults to digital audio when it expects it.

So, 1: check if that audio input is even turned on, by connecting another source. 2: If yes, check what setting in your computer is turning off analog audio when a digital connection is present. 3: If no, check that the TV is listening for DVI/HDMI audio, and then check that the soundcard is capable of sending it. If it is, you may have to prioritise that connection in a system preference panel somewhere. If it isn't, you've found your problem.
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Re: LG TV + Digital Video + Analog Audio Not Working

Postby PhoenixEnigma » Sun Nov 27, 2011 6:20 pm UTC

I have a fairly similar TV (PJ55 series, same oddly labled audio input), and just went and played around with it. All my HDMI connections are carrying audio, so if it defaults to that I wouldn't know, but otherwise it does appear to be impossible. The list of available options is pretty thin, and I tried everything I could think of, some that made no sense, some pressing of unlabled buttons, across a couple HDMI connections, including a connected-but-inactive one (in case it only worked for one), using a known-good audio source.

What video card are you using? Some ATi cards had a feature that allowed them to output audio through a DVI->HDMI adapter, but apparently not all adapters would work, and I suspect you'd have to enable it somewhere on the PC side.

If that's not an option, maybe a DVI->VGA adapter?
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Re: LG TV + Digital Video + Analog Audio Not Working

Postby Jorpho » Sun Nov 27, 2011 7:48 pm UTC

Dream wrote:Have you checked whether the audio is absent at the computer end, or the TV end? Link up the DVI->HDMI such that the audio isn't coming through, then connect an MP3 player instead of the computer and see if audio comes out of the TV. My guess is that it won't. I suspect the TV is prioritising the digital audio stream over the DVI connector, and your soundcard either does not, or isn't set to send audio via that connection.
I have now tried connecting an MP3 player to the TV's Audio In jack. Sound comes out of the TV speakers and stops as soon as I connect the video cable.

I have also used a splitter jack on the output of my sound card, and have thus verified that the computer continues to play sound even when the TV speakers aren't making any sound.

The TV manual may simply have omitted that it defaults to digital audio when it expects it.
Then the manual has not one, but two whacking grievous errors in it, as there would be no point to connecting analog audio at the same time as digital video in that case.

PhoenixEnigma wrote:What video card are you using?
It's a GTS 250, with two DVI outputs.

Some ATi cards had a feature that allowed them to output audio through a DVI->HDMI adapter, but apparently not all adapters would work, and I suspect you'd have to enable it somewhere on the PC side.
Everything I've seen thus far indicates that a DVI connection is completely incapable of carrying an audio signal.

If that's not an option, maybe a DVI->VGA adapter?
As I mentioned, that works well enough, but I can't get the same maximum resolution over VGA as I can over DVI.
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Re: LG TV + Digital Video + Analog Audio Not Working

Postby Jorpho » Sun Nov 27, 2011 8:05 pm UTC

Well, this is a bit silly...

I tried connecting my other PC (with my old GeForce 8600 GT) and could not replicate the problem! Analog audio kept playing even while this PC's digital video was being displayed.

This would appear to suggest that somehow, somewhere along the line, the TV is convinced that my other HDMI/DVI connection is carrying an audio signal when it isn't! How can this be?

To clarify, the problematic connection comprises some 25' of HDMI cable, whereas my other PC is connected directly through a single DVI cale (with adapter). I could keep running experiments with swapping cables around hither and tither, but if someone has an answer at this point, that would be most handy.
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Re: LG TV + Digital Video + Analog Audio Not Working

Postby GeorgeH » Sun Nov 27, 2011 9:40 pm UTC

It sound like your GTS250 is capable of outputting sound over DVI, but because you haven't told it not to (or switched the sound output in the control panel) it's outputting a "no sound" signal to the TV that overrides the TV's "look for sound on the analog input" function.

I haven't had this particular problem before, but the first thing I'd try (assuming you're running Windows) is changing the default playback device in Windows' sound control panel, followed by messing around in the NVIDIA control panel to see if a "disable audio passthrough" or similar option was available.

Edit - Forgot to mention that for the audio output of your card to work, you'll need to connect a cable to it from a header on your motherboard (assuming you're using onboard audio.)
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Re: LG TV + Digital Video + Analog Audio Not Working

Postby Jorpho » Sun Nov 27, 2011 10:18 pm UTC

GeorgeH wrote:It sound like your GTS250 is capable of outputting sound over DVI
But DVI does not work that way! Or am I reading this wrong?
Since the DVI specification does not support audio-transport, an interoperability problem arises when an HDMI-source drives a legacy DVI-display (such as a PC monitor), or conversely, when a DVI-source drives an HDMI-display. While HDMI and DVI compliance rules ensure that a DVI video-connection can be successfully negotiated and established (via a mutually supported display mode), the audio signal must still be transported through means outside of the DVI connection.
http://en.wikipedia.org/wiki/HDMI#Audio_support
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Re: LG TV + Digital Video + Analog Audio Not Working

Postby GeorgeH » Mon Nov 28, 2011 12:20 am UTC

DVI wasn't originally supposed to work that way, but more modern versions can do audio. I see your Wiki link and raise you one more: Wiki DVI (with special attention to the bottom bit.)
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Re: LG TV + Digital Video + Analog Audio Not Working

Postby Jorpho » Mon Nov 28, 2011 2:07 am UTC

Well. Someone should fix that first article if it's wrong, then. :?

I tried swapping the cables around and found that was definitely not the problem. And there is indeed this widget in the NVidia control panel:
hdmi_3.png
hdmi_3.png (8.38 KiB) Viewed 7142 times


Unfortunately, changing it to "Audio Disabled" does not immediately have the desired effect. Further testing/reboots are necessary.

As I recall, this computer's motherboard does not have any variety of internal SPDIF header, so I never connected the card to anything.

EDIT: Giving this a shot:
http://currysauce.org/2010/03/20/how-to ... ics-cards/

EDIT2: That's sorted it! Huzzah! Now to fix that article.
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