John DiLorenzo wrote:
I'm planning my myth setup and I'm a little confused about how to
handle capturing and playing back surround sound. Here's the plan so far:
Backend/frontend with a single pvr-150 (for now) and a Geforce MX460.
The backend will be connected to a Scientific Atlanta digital cable
box. The only digital audio out is a digital coax. I have a tuner
that will accept an optical input.
It's clear that I need a sound card with an optical out to output
audio to the receiver, but how do I get 5.1 captured in the first place?
Do I:
1. Get a soundcard with both coax and optical ports and somehow
configure coax for input and optical for output?
2. If I rely on the pvr-150 for capturing the audio by using coax
cable from the digital tuner to the 150, will it capture in 5.1? If
so, would I be sacrificing video quality by not using s-video?
3. Or am I missing something else?
PVR-150 records NTSC or PAL.
NTSC/PAL don't do 5.1 channel audio--they support only 2-channel stereo
sound.
Therefore, PVR-150 cannot record 5.1 channel audio.
However, Dolby Surround ( http://en.wikipedia.org/wiki/Dolby_Surround )
is a technology whereby multiple audio channels (4.0 channels) are
encoded within a standard 2-channel (stereo) signal and decoded using a
Dolby Pro Logic ( http://en.wikipedia.org/wiki/Dolby_Pro_Logic )
decoder. Often, when a show is broadcast (on digital stations) in Dolby
Digital=AC-3=5.1 ( http://en.wikipedia.org/wiki/Dolby_Digital ), the
analog stations transmit Dolby Surround encoded in the stereo signal.
The PVR-150 records the stereo signal broadcast with the show, so--in
theory--it would be possible for Hauppauge to support Dolby Surround.
However, the PVR-x50's do not contain a Dolby Surround decoder--instead
only a stereo decoder--so only two channels of audio are encoded in the
stream.
However, most ALSA drivers will automatically replicate the left- and
right-front channels to the left- and right-rear (and surround if you
have a 7.1 channel setup) speakers since it has only a minor effect on
the perceived positionality of the sounds. If your driver doesn't, you
can easily add a translation table to your .asoundrc to do it yourself.
If you really want 5.1 channel, though, you'll have to go to a digital
video broadcast technology (like HDTV (US) or DVB).
Mike
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