HDMI out to TV, no sound

[Russell Reiter]

I had a further look at this information on HDMI and it seems to me
this is what jackd is for. A udev event, although you might not even
need that daemon to try this. I have my own problems with trans coding
video and audio signals at the moment, this problem is a distraction
and why I'm top posting.

Try plugging the cable connected to the tv into the pc and use #lspci
see what pin 19 shows on the bus when hot plugged. Then try udevadm
info --attribute-walk <path and name> man udev, to see how this works.
Assuming you get results, you might be able to use a hot plug event to
connect the audio stream(s), using a udev rule.

The hdmi cables audio transport layer carries LPCM sound, surround
sound if your tv has output for that, which it probably does in the
form of, hdmi in and hdmi out and unlike midi no throughput. That
transport layer will convey the digital signal to the tv for trans
coding. Shielding the signal from the "copper"  noise. There are three
shields for the data and one for the bus clock. The shielding signals
make for more efficient multiplexing of the signal, remember it's an
RF signal. Alternatively if the tv does not do its own trans coding
and is expecting something else in its TDMS data stream, that
condition could most likely be overcome by udev re-assignment as well.
In order to pass the signal through the sound card and then mix it
back in to the stream, the appropriate udev rule could be applied on a
hot plug event. I believe this is where jackd would fit in, making it
easier to allow for the lack of direct pin assignments to digital
device outputs.

aplay -L will show what audio devices are detected. Although the lack
of one to one pin assignment, as noted in the links, may be
insurmountable without the jackd daemon to handle the kernelspace
mappings.

There is a lot of RF noise when you take an analog audio signal
directly from the back of the computer. Better to deliver it to a
"clean" switch digitally before converting it to analog.


On Fri, Jun 3, 2011 at 11:14 PM, D. Hugh Redelmeier <hugh-pmF8o41NoarQT0dZR+AlfA at public.gmane.org> wrote:
> | From: Thomas Milne <thomas.bruce.milne-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org>
>
> | If I have an HDMI out on my video card, and I connect to my TV, is that all
> | I need? Should that convey the sound? The manual for the video card says
> | nothing on the subject. There were no extra cables or anything, though some
> | people seem to be saying you need to connect the video card to a sound
> | device?
>
> It depends on the card.  I'd bet almost all modern cards with HDMI-out
> also support sound out on HDMI.
>
> You were having problems with your GeForce GT 520 card.  That card
> would have sound out.  See section 6.1.4 in
> <ftp://download.nvidia.com/XFree86/gpu-hdmi-audio-document/gpu-hdmi-audio.html>
> (Not sure why it is XFree86.)
>
> There are different kinds of audio supported on HDMI.  Not all types
> are supported by all cards.  From <http://en.wikipedia.org/wiki/HDMI>:
>
>    For digital audio, if an HDMI device supports audio, it is required to
>    support the baseline format: stereo (uncompressed) PCM. Other formats
>    are optional, with HDMI allowing up to 8 channels of uncompressed
>    audio at sample sizes of 16-bit, 20-bit and 24-bit, with sample rates
>    of 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz and 192
>    kHz.[21][45] HDMI also supports any IEC 61937-compliant compressed
>    audio stream, such as Dolby Digital and DTS, and up to 8 channels of
>    one-bit DSD audio (used on Super Audio CDs) at rates up to four times
>    that of Super Audio CD.[45] With version 1.3, HDMI supports lossless
>    compressed audio streams Dolby TrueHD and DTS-HD Master Audio.[45] As
>    with the YCbCr video, device support for audio is optional.
> --
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