Jean Fredette wrote:


I have no idea what the third choice switches to though.

SPDIF:

That's either TOSLink (glowing red LED color, leaks through
rubber capped square connector on back of PC), or it
can be delivered by legacy copper coax connection (RCA/Cinch
connector, same style connector which peppers the back
of large screen TV sets). The SPDIF connector isn't
keyed, so it can "go in the wrong holes", and with RCA/Cinch
you do have to be careful. Audio doesn't have the same
attention to detail as computer connectors. At least
a few things on computers "won't fit" to help prevent
you from blowing stuff up.

You can see rather poor examples of both here. (The RCA/Cinch
should be showing more metal reflections in the picture.)

https://www.dx.com/p/spdif-toslink-t...7#.XJK1YaUwDQx

The TOSLink is a fiber optic connection that uses plastic "dental" fiber,
the same kind of fiber that conducts light for dental work.
The connector is squarish on its perimeter. On the "out"
connector, you would see red LED light "leaking" from
under the rubber cover on the port. You peel back the
rubber cover, before inserting the cable.

The RCA/Cinch is for the copper equivalent of the signal.

https://en.wikipedia.org/wiki/RCA_connector

The signal in that case, is carried on coaxial cable, with
RCA/Cinch on either end. The signal might have a characteristic
impedance of 50 ohms. The RCA/Cinch is a lousy choice for
maintaining a 50 ohm environment (it's not an RF
connector). When you look at cable TV connectors,
F-series maybe, those are 75 ohms and are going to be
closer to being the proper impedance for their application.
RCA/Cinch are used for:

Audio speakers
Line In audio
Composite video (red/yellow/white on TV back)
YPbPr video ?
SPDIF

The Speaker Out on a high power stereo, would likely
have sufficient amplitude to destroy the SPDIF-In on
your AV receiver, if connecting the cable to the wrong holes.

But in any case, both TOSLink/RCA SPDIF standards carry a 6Mbit/sec
stream, sufficient for two channels of high definition
audio. An alternate format, is to support four channels
using "fewer bits", which would not particularly be
an audiophile choice. I keep seeing references to that
mode, but nothing seems to use it.

When computers first got "digital audio", it was just
that RCA connector. It was only later that TOSLink
optical output was offered, and at first, there
was an adapter card you put in a PC slot with the
simple driving components (LED and switching transistor).
Later, TOSLink got put in the I/O plate area, and
PCs could have both TOSLink and SPDIF at the same time.
When you have both, you can drive two home theater
receivers at the same time, since SPDIF is unidirectional
and the PC only "sends" to each AV receiver. The TOSLink
and RCA, are copies of the same signal.

PCs have also had SPDIF-in, but that was only
via the adapter card that sits in a slot. The reason
the industry tried to "hide" that one, was DRM and
"making perfect copies" of audio content. They
didn't want to encourage people to use computers
to record digital audio. But the *******s did have a way
to "get even", as some 24 bit audio sent that way,
had the 8 least significant bits "set to zero"
to "ruin" the resolution, making perfect copies
impossible. So while the user might have a big
**** eating grin on their face "recording 24 bit audio",
they were in fact only getting 16 bit copies. You could
always examine a recording with your hex editor,
and figure out you were "ripped off".

Paul