[mythtv-users] Can mythtv (or mplayer/xine through mythtv) upmix 5.1 sound in 6.1 or 7.1?

Stephen P. Villano stephen.p.villano at gmail.com
Sat Oct 5 21:28:21 UTC 2013


On 10/5/13 4:14 PM, Eric Sharkey wrote:
> On Sat, Oct 5, 2013 at 11:14 AM, Marc MERLIN <marc_mtv at merlins.org> wrote:
>> On Sat, Oct 05, 2013 at 10:40:46AM -0400, Eric Sharkey wrote:
>>>> Digital. Otherwise 5.1 wouldn't work right either :)
>>> No, that's not the case.  That's precisely how "Pro Logic" surround
>>> sound works.  The audio from multiple channels are downmixed to only 2
>> You're right. I just never took that seriously. Maybe it works better than
>> I know.
> It works better than you might think.
>
> As a solution to the problem of "How do I send surround sound
> information over broadcast television with an enormous installed base
> of stereo/mono receivers encoded in such a way that no additional
> bandwidth is used and the existing sets still sound ok but surround
> sound sets can get some differentiation between front and back
> sounds?" it's quite an ingenious system.  As a solution to "How do I
> start from scratch and encode multichannel audio without worrying
> about backward compatibility?" it's complete rubbish, of course, but
> 20+ years ago it was about as good as we could expect to get.
>
> It's really quite amazing to me how the tv signal went from a black
> and white mono signal and added color, stereo, surround, closed
> captioning, etc. without breaking the ability of older sets to receive
> the signal, up to the transition to digital.
Not all that amazing. There was enough room as technology advanced to
add color reference information in, though the 60Hz field refresh
frequency did have to get lowered to 59.94Hz. The old 525 lines of
information was based upon old vacuum tube maximum frequency response.
Adding in quadrature phase signal processing permitted color to be added
into the luminance signal. The horizontal back porch had sufficient room
to add in the color synchronization burst.
The audio was already FM, so adding in the stereo also could be added in
with minimal trouble as technology improved and sum and difference
signals could be multiplexed onto signals that would not be able to
reproduce the 19khz pilot tone.
It was all additive, clever implementations upon a prior framework that
maintained compatibility with prior generation hardware.

Amazing is what we now can do with digital, even for someone who worked
with early commercial digital processing for studio tape machines back
in the early 1980's (and obviously, on televisions before and well into
VLSI and surface mount components, before moving on to computers).
I'll not even go into what we now can do with plastics, where if I said
we'd do it 40 years ago, I'd have ended up in a room with rubber
wallpaper...

>> But this puts me back to square 1: I haven't found any alsa config to do
>> this, or any other way with mythtv (which I was just told there isn't inside
>> mythtv itself).
> 6.1 configurations just aren't that common.  You're the first person
> I've heard of that actually has one.  You may need to code this one up
> yourself.
>
> Eric



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