[mythtv-users] noobie sound questions

[nate s]

I don't have time to answer all the points atm (and others may be able
to do a better job,) but I'd go with the cmedia chip over the realtek.
 AFAIR, it is merely the ADC (analog-digital-converter,) and the
realtek ones are poor quality (the cmedia ones aren't great either,
but much better)

-Nate


On Sat, 20 Nov 2004 20:11:34 -0500, Jamie Stotz <wstotz at toad.net> wrote:
> I've been digging through the list for a few months in preparation for
> building my first Myth (and Linux) box. While trying to decide which
> motherboard to buy I realized I don't understand enough about how sound
> is handled to know which features I need.
> 
> I plan on using an nForce2 mATX motherbord and a Hauppauge PVR250 tuner
> card. My main use will be to time shift standard def TV programing and
> feed it through my AV receiver to a standard def TV. Since I already
> have a stand alone DVD player, I probably won't be using it to watch
> commercial movies. However, I might want to remove commercials and
> record TV to DVD's if my hard disk fills up. I won't be using MythMusic
> or MythGame.
> 
> Here is my current understanding of how the sound works. Please add or
> correct anything.:
> 
> 1. SDTV signals ( over-the-air or through analog cable TV ) can contain
> mono or 2 channel stereo audio signals, depending on the source
> material.
> 
> 2. Additionally, the 2 channel stereo signal can have a Dolby Prologic
> surround sound signal encoded in it.
> 
> 3. This analog stereo signal (with or without the embedded surround
> signal ) is captured and digitized by the PVR 250 tuner card and stored
> un-decoded in the MPEG2 file that also contains the video.
> 
> 4. Upon playback, this stereo data is separated out by the MPEG2
> playback software and sent to:
> 
> 5. Some collection of sound related software and hardware on the
> motherboard or sound card. ( I'm kind of fuzzy here )
> 
> 6. The black box in #5 can:
> 
> 6a: Convert this digital stereo data into an analog waveform and send
> it out the analog out port ( 1/8" stereo jack ) to my AV receiver where
> the surround signal ( if present ) is extracted and sent to the
> appropriate speakers.
> 
> or
> 
> 6b: Send the digital stereo data out the S/PDIF optical/coax port to my
> AV receiver where the surround signal is extracted and sent to the
> appropriate speakers?
> 
> or
> 
> 6c: Extract the surround data from the digital stereo data and send the
> digital surround data out the S/PD/IF optical/coax port to my AV
> receiver where the surround signal is extracted and sent to the
> appropriate speakers?
> 
> So, I'm wondering:
> 
> A. If 6b and 6c are possible, is there any noticeable advantage in
> quality over 6a? So do I really need a S/PDIF port for TV or only if I
> want to play commercial DVD's?
> 
> B. Some motherboards use the Cmedia CMI9739 sound chip, others use the
> Realtek ALC650. What function(s) does this chip actually perform? I
> assume is is involved with #5 and 6 above. Should I care which chip is
> used?
> 
> C. I imagine that if I was going to play commercial DVD's the S/PIF
> port would be important. But since I have an AV receiver with 5.1
> support I don't need the motherboard to decode 5.1 surround.
> 
> D. Does the nVidia MCP-T chip offer anything useful for MythTV/Linux
> that the regular MCP doesn't?
> 
> Thanks for your help. I'll be posting some video related question soon.
> 
> Jamie
> 
> 
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