Newsgroups: rec.audio.tech
Subject: Re: XLR or RCA connections?
References: <[email protected]> <[email protected]>
Dave Cull  writes:

> Bobzilla wrote:
> 
> > Questions:
> > 
> > 1. Is RCA better than XLR or vice versa?
> > 2. What is the diff. between balanced and unbalanced?
> > 
> > Thanks for all of your help
> 
> 
> XLR connectors are better 'cause they're balanced.  

XLR connectors itself are not balanced. Those connectors
can be used to carry both balanced and unbalanced signals.
(by comparision RCA connectors are always unbalanced).
Practically all professional audio equipments that have
XLR connector,but I have heard some expections to rule
(so there is no guarantee that XLR connector means balanced
audio signal, or even audio signal at all in that connector
if the equipments are not audio equipments ..)

>This means that they 
> use a transformer to cancel out E.M. noise.  

Balanced connections will cancel out noise very effectively,
but balanced connections do not autiomatically mean that there
are transformer used in those. There are electrically balanced
connections as well, which are built around operational amplifiers.
Those electrically balanced interfaces do practically the same things
as transformer balanced, although they are cheaper and not good
in cancelling out EM noise (and can easily sound better than
balanced connection which uses not very good transformer).

So there are balanced connections with and without transformers.

> They send the signal 180 
> degrees out of phase down 2 conuctors.  

In balanced interconnections nearly always there are two signals
180 degrees out of phase on two signal connections. This signal
arrangement makes the audio signal a "differential signal" between
those audio wires. This is how
it is practically always done and is the best approach.  The output
impedances of the drivers driving those lines have same output impedance
or those signal wires are connected to ends of the floating secondary
coil of the output balancing transformer.

On balanced output one should note that there is a variety which is
called "impedance balanced". it has the balancing properties of
same impedance on both signal wires, but the signals are not out
of phase (one wire carries the signal and one has no signal). This
"impedance balanced" output works also well as balanced output with
balanced input, although it's performance is somewhat poorer
than the balanced with "differential signals" on audio wires.


> At the input of the second 
> device, it puts the signals back together in-phase.  

That's true. And this putting back works also with
signals not in phase but are "impedance balanced" as well.

>The 2 types of 
> connectors which use a balanced system are XLR and TRS (tip, ring, 
> sleeve).  

Those are the most commonly used connectors in audio world for balanced
connections. In practice balanced audio can be carried with any connector
which has at least two signal connectors and ground connection possibility.
One such example are multipin connectors used for some audio applications
to carry multiple of audio channels using one connector (used to connect
sometimes stage connector boxes or effect racks to mixers on some 
installations).

In paractice balanced audio signal (at least transformer isolated at
least in one end) can be carried with two wires only through unshielded
twisted pair cabling. Normal telephone uses this and also some adapters
which run audio/video signals through CAT5 structured cabling which uses
RJ-45 connectors (one audio signal on those for one wire pair). Because
of no shielding in cable the performance against EMI is not so good,
but they work acceptably in not very demanding applications in not
very demanding enviroments. Professional live stage audio field is both
demanding in sound quality and demanind noise enviroment so shielding
and balanced interconnections are there essential to make thing work
without too much noise entering to the system. Professional audio
studio is somewhat easier enviroment, but even much more demanding on
sound quality, so same techniques are needed there also.

> Use balanced connections wherever you have the means, 
> resources: especially where you have long runs of cable to run (ie: from 
> the FOH desk to amps on-stage). 

You are definately right. 

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/