all right my name is Dave Rat and here I am to talk about crosstalk in
shielded cat5 cable running analog downa data cable and do some testing to
determine whether or not in a real-world situation in real-world situations
crosstalk between the various twisted pairs is a an issue that is audible or a
concern for us
when running analog down and data cable especially a cat 5e that
has twisted pairs that are not individually shielded and there's purely
an overall shield protecting the pair's from the outside influences one of the
concerns is if these pairs are not being shielded from each other if you were to
run a very high level signal down one pair would that bleed into the other
pairs at a noticeable or audible level
which is obviously something we don't
want to have happen to us in a live or studio environment where we can hear the
sound of the wrong instrument coming down that channel one may think or what
makes logical sense that there should be this is a hundred meters long I used an
extra long cable to magnify any issues that may occur and having them unshielded
it almost defies logic to think that there wouldn't be some sort of crosstalk
issue conversely the quality of the twisted pairs in a data cable if those
pairs are perfectly twisted and if the balanced mic pre on the front end
of the mixing board is good enough then any signal that's influenced upon those
twisted pairs should be canceled out by the balanced mic pre, additionally if the
pairs are twisted well enough they shouldn't radiates a lot of energy they
should radiate almost no energy it should cancel it out before either
leaves the cable so the design of the cable is such that it should have no
crosstalk or very minimal crosstalk due to the quality of the pair's as well as
the balanced mic pre on the other hand not having the shielding is a definite
concern and the only real way to find that out is to do some testing so this
is what I've got I've got a SoundTools 100 meters SuperCat cable I've got a
pair of a set of cat tails with female xlr's that's plugged into a pink, I'm
sorry not a pink noise, a music source
it'll get to a different song by the time I get there it's going to a music
source and then the other three lines of the four channels are going to an Audix
om7 which is an extremely low-level dynamic mic transformerless that's six
to eight DB lower output than just about any other mic on the market compared to
a beta58 or sm58 or others, I've got another low-level dynamic mic a
Sennheiser 441 and for a condenser mic I've got a Neumann U89 set into
cardioid mode, super cardioid mode so that we've got kind of a various
reference point of something that we might run into in the live environment
and having a line level cable you can see that the you may be able to see
the music is clipping the channel I'm going to turn that down a little bit so
I'm gonna run the music about just into clip
and the gain differential on these mic pre's I've got the Audix mic turned up
almost all the way so it's about +55 on the mic pre, I've got the music
turned down almost all the way so it's it almost -10 so we're about at
least 60 DB differential in gain on the mixing console between the microphones
and the music signals and then what I'll do is we'll turn up each mic
independently and we'll see if we hear any of the music so first the music is
and now we will go to let's start with the Audix this up the speakers very
close it's right here behind me and we can see that I'm far away and we're just
on the verge of feedback and the music is completely inaudible now we'll go on
to Sennheiser
he hey hey and again no audible music and just to show the music still
there and the music is clipping pretty hard on the console now and finally
the Neumann
try not to give you any feedback here that's too painful and again not even
the slightest hint of music is bleeding through, now I will try all three at the same time
and even though we're running a hundred meters of twisted pairs that are not
individually shielded from each other and we're running a very high level line
level signal down one of the channels the other three channels with mic level
inputs and at very high gain show absolutely no sign of the music in the
form of crosstalk so I would say that based on this I'm pretty comfortable
that crosstalk even in a non individually shielded data cable is
not an issue cool