[mythtv-users] [OT] Digital Audio Formats

Brad DerManouelian myth at dermanouelian.com
Fri Jan 4 00:16:56 UTC 2008

On Jan 3, 2008, at 3:45 PM, clemens at dwf.com wrote:

> Im confused here.
> When I see references to PC Audio Cards I see S/PDIF as what appears  
> to
> be a 2 channel digital audio format (both datalink and physical  
> layer).

S/PIDIF can do multi-channel audio. I use it to go from my motherboard  
that has S/PDIF built it to my Pioneer receiver than accepts S/PDIF.

> When I see references to Home Theater products (ok HD products), I see
> references to HDMI which seems to be a multichannel (video) and audio
> format (in some cases it seems to be up to 9.1 channels?)

Commonly, people tend to either do 2-channel (stereo), 5-channel (or  
5.1 with a subwoofer) or 7-channel (or 7.1 with subwoofer) which is  
becoming more popular. You can't get any more audio channels than that  
in any video format you can purchase for home use.

> There are other references to just 'digital audio', with who knows  
> what format?

Yeah. Who knows? Not-Analog can mean lots of things. :)

> There appear to be amplifiers that take HDMI in, but I haven't seen  
> anything
> that takes S/PDIF in.

Lots of them do. Not sure where you're looking. S/PDIF has been a  
standard a lot longer than HDMI so maybe companies are just all proud  
of their new connectors and forget to mention they do S/PDIF.

> Anyone have a reference that explains all this (plus coax vs optical  
> versions
> of each, if applicable...)

S/PDIF can have RCA (http://en.wikipedia.org/wiki/RCA_connector), BNC (http://en.wikipedia.org/wiki/BNC_connector 
) or TOSLink (http://en.wikipedia.org/wiki/TOSLINK) connectors.
I recommend TOSLink if you have the option. You can physically see  
light passing through the cable at the end of the connector when your  
motherboard is spitting out S/PDIF through it. It helps a LOT when  
diagnosing issues. You generally won't see BNC connectors on consumer  
products. They usually come with both RCA and TOSLink connectors,  

> Sometime this coming year I will be springing for a new HD tv, and  
> would like
> to know WHAT I need to process the audio.
> And WHAT ADDITIONAL I need to have specified if I want to get audio
> from my PC, from something like MythTV.

The only thing I can say is not to use HDMI audio as your first  
choice. HDMI couples video and audio signal into the same cable which  
in my opinion is a no-no. Sure, it's easy for consumers to plug in 1  
connector to each end and have it work, but I've experienced  
interference with this. I have an HDMI cable from my PS3 to my TV  
which passes it to my receiver and when I got Rock Band, I could  
barely stand listening to the noise that came through so I switched to  
S/PDIF form the PS to my receiver and it's perfect. Not sure if it's  
my TV messing it up when passing through, but it was REALLY bad.

> And just for good measure, I never see anything mentioned about bit  
> rates,
> which from the Audio cards it is possible to change.

Most receivers are only happy with standard bitrates. For instance,  
mine doesn't understand anything other than 48k or 44.1k and I believe  
both have to be 24-bit.

Some more interesting stuff here, too:

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