[XCSSA] Sound issues with "The Darkness"

[X-otic Computer Systems of San Antonio]

Coaxial digital audio came first, back in about 1984.  Then came  
optical.  Some units use one, some units use the other, most good  
receivers accept both, and many devices output both.

They actually have exactly the same pulses.  To convert coaxial  
digital to optical, you merely have a circuit that lights the LED  
when the voltage is high.  And vice versa.

You need these adapters when you want to connect two pieces of gear  
that don't use the same kind of connection.  In my vast home audio  
system, this problem has come up several times.

There's also a third way, using balanced cables, usually with XLR  
connectors.  Usually, that's a slightly different protocol, called  
AES/EBU, used mostly by music professionals.  You can also send AES/ 
EBU down coaxial or optical, but the "best" approach is with balanced  
110 ohm cables.

The standard coaxial is called S/PDIF (Sony Phillips Digital  
InterFace).  The standard optical is called Toslink, though sometimes  
it's also called SPDIF, since it's exactly the same pulses.

Advantages?  Minor differences, nothing much to speak of.  With the  
optical connection, you are absolutely assured of not creating any  
ground loops, which are tough to deal with very complicated A/V  
systems.  However many people believe the coaxial connection is  
better: because the pulses are "sharper" there's less "jitter"  
introduced.  I don't believe this has ever been "proven" to make an  
audible difference using blind testing, but many people believe it is  
anyway, and it can be measured.  (Now we also have "jitter immune"  
decoder chips anyway, so it doesn't much matter.)  And, even if you  
do create a ground loop with a coax connection, it's typically not  
big enough to interfere with the digital signal itself (though it  
could produce some effect on your TV).  And actually, the coax  
connection may be transformer linked so it can't produce ground  
loops.  (I think the standard requires transformer linkage, but  
sometimes manufacturers cheat and leave it out.  Maybe that's why the  
optical method was invented.)

Serious audiophiles typically use coax in preference to optical when  
both are available.  Cheaper gear typically uses optical.  But the  
differences are probably negligible.

Long ago, the plastic optical cables were very lossy and you couldn't  
run Toslink more than 5 feet.  Nowadays you can find 30' optical  
cables that work fine.  There are glass fiber optic cables available  
also, but they are much more expensive and harder to find.  Coax also  
works fine at 30 feet, though theoretically you should use only 75  
ohm cable, and not standard audio cable.  Once again, it probably  
doesn't make any difference with recent equipment.

So, it's just one of those things were there are two ways of doing  
something, both pretty much the same, and because of that, you either  
have matching equipment or need adapters.

You can also send digital audio down HTMI, USB, and Firewire  
connections.  Serious professional gear (used in music mixing and  
mastering) tends to use dedicated Firewire connections.

Charles




On Feb 3, 2008, at 9:53 PM, X-otic Computer Systems of San Antonio  
wrote:

> I went to Altex today and they had a optical to coaxial adapter.  
> I'm confused. I thought that optical was used primarily for audio  
> unless I missed a memo somewhere.
>
> I also stopped by Bjorns to see if they had anything interesting.  
> They have the Sony 11" OLED set that was recently unveiled at CES.  
> They had it in a glass case, and for the asking price of $2,500 it  
> better be inside one, but wasn't turned on. I really wanted to see  
> it in action so I could judge this thing for myself.
>
> BTW, does anybody know if there are any computer style speakers  
> with optical inputs? Just curious.
>
> --Robert Allen Rusk (RARusk)
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