"infamis" wrote ...
I always thought for a sine wave, you need a 2 "wires"

Any electrical circuit, whether it is carying AC (sine
waves, audio, mains power, etc.) or DC (like your car
battery) takes a complete circuit.

and that the flow of electricity changed depending on
the analog values.

So far, so good.

In other words, you need a positive & a negative.

You may be confusing yourself here. There is no
"positive" and "negative" in AC because it changes
several thousand times every second.

For example, a waveform "peak" would be a speaker's
cone moving outwards and back to 0, while a trough
would be the cone moving inwards & back to 0. Translating
this to wires to mean that the electrons flow from A-B
while the voltage increases & goes back to 0 and vice
versa (for a trough, the electrons flow from B-A while
voltage increases & goes back to 0)

That's why I don't understand how RCA & mini-jacks
work since
a) RCA...one wire connected to ground. Where is the
signal coming from? Ground doesn't generate the audio
signal?

The AC signal is carried on the inner pin of the RCA jack
and the ground provides the return path for the complete
circuit. Just as the body of your car carries the return path
for the battery power that runs the starter motor, the power
that runs your lights, and even the audio that goes to the
rear speakers, etc.

b) Common ground...how can that work, shouldn't there
be four different slivers on the mini-jack?

Yes, one method of carrying signal current uses a
BALANCED line where there are two wires, neither of
which are ground. As one side is going positive, the other
side is going an equal distance negative. This method is
typically used for microphones and professional audio
equipment. Because it is more expensive, consumer
electronic equipment tends to use UN-balanced kinds
of connections. Clearly this is quite workable in hundreds
of millions of cases around the planet.

If someone could just explain how a sine wave works
on RCA & (stereo) mini-jacks, that would be very
helpful. In other words, just point \out where the negative
& positives are (as when you connect a speaker, you
need a negative & a positive).

Typical consumer equipment uses UN-balanced connections.
Think of a kid on a pogo stick. The movement is all referenced
against ground. But the ground has to be there even if it
doesn't move. You can't use a pogo-stick in outer space.

Most professional equipment uses BALANCED connections.
Think of two kids on a see-saw (teeter-totter). When one
goes up, the other goes down (and alternating vice-versa.)