[mythtv-users] One HDMI question from (Hijacked): HDMI sound issues

[Gary Buhrmaster]

On Fri, Aug 30, 2013 at 2:11 PM, Joseph Fry <joe at thefrys.com> wrote:
...
> First of all, most "electric" conductors don't carry "fundamentally
> analog signals".  While there are certainly places where a digital
> signal is encoded on an analog carrier frequency (modems)... most
> digital interconnects are pure digital.  Essentially, if you hook a
> o-scope to the lines in the cable you will see a nice square signal of
> a fixed pulse rate and voltage differential.  This is no different
> than the signal traveling between transistors in your CPU, other than
> it having a much slower pulse clock and much higher voltage
> differential, and I don't think you would argue that signals within a
> CPU are "fundamentally analog".

Actually, those "square" waves are anything but.  With a
"real" scope, you will see a small ramp up, and usually an
overshoot, and some (minor) ringing, etc.  Voltage does
not change instantaneously (except in those "friction-less
pulley" textbooks).  While one can model digital circuits
as being on/off at lower speeds (even though there is a
point at which those on/off transistors are in their linear
region), at very high switching speeds what you have is
an analog transmission line, with all the issues that
implies.  Sure, the result is interpreted as a 0 or 1, but
sometimes one is actually looking at the slope of the
signal (ex. rising) to determine the next bit value.

Gary