<s>
Balanced	B-Protocol
audio	I-Protocol
is	O
a	O
method	O
of	O
interconnecting	O
audio	O
equipment	O
using	O
balanced	O
interfaces	O
.	O
</s>
<s>
The	O
connectors	O
are	O
usually	O
three-pin	O
XLR	B-Device
or	O
TRS	B-Device
phone	I-Device
connectors	I-Device
.	O
</s>
<s>
Many	O
microphones	B-Application
operate	O
at	O
low	O
voltage	O
levels	O
and	O
some	O
with	O
high	O
output	O
impedance	O
(	O
hi-Z	O
)	O
,	O
which	O
makes	O
long	O
microphone	B-Application
cables	O
especially	O
susceptible	O
to	O
electromagnetic	O
interference	O
.	O
</s>
<s>
Microphone	B-Application
interconnections	O
are	O
therefore	O
a	O
common	O
application	O
for	O
a	O
balanced	O
interconnection	O
,	O
which	O
allows	O
the	O
receiver	O
to	O
reject	O
most	O
of	O
this	O
induced	O
noise	O
.	O
</s>
<s>
Many	O
other	O
components	O
,	O
such	O
as	O
graphic	O
equalizers	O
and	O
effects	O
units	O
,	O
have	O
balanced	B-Protocol
inputs	I-Protocol
and	O
outputs	O
to	O
allow	O
this	O
.	O
</s>
<s>
Balanced	B-Protocol
audio	I-Protocol
connections	O
use	O
a	O
number	O
of	O
techniques	O
to	O
reduce	O
noise	O
.	O
</s>
<s>
A	O
typical	O
balanced	B-Protocol
cable	I-Protocol
contains	O
two	O
identical	O
wires	O
,	O
which	O
are	O
twisted	O
together	O
and	O
then	O
wrapped	O
with	O
a	O
third	O
conductor	O
(	O
foil	O
or	O
braid	O
)	O
that	O
acts	O
as	O
a	O
shield	O
.	O
</s>
<s>
A	O
transformer	B-Algorithm
may	O
also	O
be	O
used	O
instead	O
of	O
an	O
active	O
input	O
stage	O
.	O
</s>
<s>
The	O
separate	O
shield	O
that	O
’s	O
commonly	O
provided	O
in	O
a	O
balanced	B-Protocol
audio	I-Protocol
cable	O
also	O
yields	O
a	O
noise	O
rejection	O
advantage	O
over	O
an	O
unbalanced	O
two-conductor	O
arrangement	O
(	O
such	O
as	O
used	O
in	O
typical	O
home	O
stereos	O
)	O
where	O
the	O
shield	O
must	O
also	O
act	O
as	O
the	O
signal	O
return	O
wire	O
.	O
</s>
<s>
Therefore	O
,	O
any	O
noise	O
currents	O
induced	O
into	O
a	O
balanced	B-Protocol
audio	I-Protocol
shield	O
will	O
not	O
be	O
directly	O
modulated	O
onto	O
the	O
signal	O
,	O
whereas	O
in	O
a	O
two-conductor	O
system	O
they	O
will	O
be	O
.	O
</s>
<s>
Signals	O
are	O
often	O
transmitted	O
over	O
balanced	O
connections	O
using	O
the	O
differential	O
mode	O
,	O
meaning	O
the	O
wires	O
carry	O
signals	O
that	O
are	O
equal	O
in	O
magnitude	O
but	O
of	O
opposite	O
polarity	O
to	O
each	O
other	O
(	O
for	O
instance	O
,	O
in	O
an	O
XLR	B-Device
connector	I-Device
,	O
pin	O
2	O
carries	O
the	O
signal	O
with	O
normal	O
polarity	O
,	O
and	O
pin	O
3	O
carries	O
an	O
inverted	O
version	O
of	O
the	O
same	O
signal	O
)	O
.	O
</s>
<s>
Though	O
the	O
signal	O
level	O
would	O
not	O
be	O
changed	O
due	O
to	O
nominal	B-Algorithm
level	I-Algorithm
standardization	O
,	O
the	O
maximum	O
output	O
from	O
the	O
differential	O
drivers	O
is	O
twice	O
as	O
much	O
,	O
giving	O
6dB	O
extra	O
headroom	O
.	O
</s>
<s>
generally	O
provide	O
balanced	B-Protocol
inputs	I-Protocol
and	O
outputs	O
,	O
typically	O
via	O
XLR	B-Device
or	O
TRS	B-Device
phone	I-Device
connectors	I-Device
.	O
</s>
<s>
In	O
critical	O
applications	O
,	O
a	O
100%	O
balanced	O
circuit	O
design	O
can	O
offer	O
better	O
signal	O
integrity	O
by	O
avoiding	O
the	O
extra	O
amplifier	O
stages	O
or	O
transformers	B-Algorithm
required	O
for	O
front-end	O
unbalancing	O
and	O
back-end	O
rebalancing	O
.	O
</s>
<s>
Three-pin	O
XLR	B-Device
connectors	I-Device
and	O
quarter-inch	O
(¼	O
 "	O
or	O
6.35mm	O
)	O
TRS	B-Device
phone	I-Device
connectors	I-Device
are	O
commonly	O
used	O
for	O
balanced	B-Protocol
audio	I-Protocol
interfaces	O
.	O
</s>
<s>
Many	O
jacks	O
are	O
now	O
designed	O
to	O
take	O
either	O
XLR	B-Device
or	O
TRS	B-Device
phone	I-Device
plugs	O
.	O
</s>
<s>
With	O
XLR	B-Device
connectors	I-Device
,	O
pins	O
1	O
,	O
2	O
,	O
and	O
3	O
are	O
usually	O
used	O
for	O
the	O
shield	O
(	O
ideally	O
connected	O
to	O
the	O
chassis	O
)	O
and	O
the	O
two	O
signal	O
wires	O
,	O
respectively	O
.	O
</s>
<s>
(	O
The	O
phrase	O
"	O
ground	O
,	O
live	O
,	O
return	O
"	O
,	O
corresponding	O
to	O
"	O
X	O
,	O
L	O
,	O
R	O
"	O
,	O
is	O
often	O
offered	O
as	O
a	O
memory	O
aid	O
,	O
although	O
the	O
second	O
signal	O
wire	O
is	O
not	O
a	O
"	O
return	O
"	O
in	O
the	O
case	O
of	O
differential	O
signaling	O
)	O
On	O
TRS	B-Device
phone	I-Device
plugs	O
,	O
the	O
tip	O
is	O
signal/non	O
-inverting	O
,	O
the	O
ring	O
is	O
return/inverting	O
,	O
and	O
the	O
sleeve	O
is	O
chassis	O
ground	O
.	O
</s>
<s>
Reversing	O
the	O
polarity	O
at	O
any	O
other	O
point	O
in	O
a	O
balanced	B-Protocol
audio	I-Protocol
system	O
will	O
also	O
result	O
in	O
this	O
effect	O
at	O
some	O
point	O
when	O
it	O
is	O
later	O
mixed-down	O
with	O
its	O
other	O
channel	O
.	O
</s>
<s>
Telephone	O
lines	O
also	O
carry	O
audio	O
through	O
balanced	O
circuitry	O
,	O
though	O
this	O
is	O
generally	O
now	O
limited	O
to	O
the	O
local	B-Architecture
loop	I-Architecture
.	O
</s>
<s>
This	O
uses	O
XLR	B-Device
connectors	I-Device
and	O
twisted-pair	O
cable	O
with	O
110-ohm	O
impedance	O
.	O
</s>
<s>
As	O
a	O
last	O
resort	O
a	O
balanced	B-Protocol
audio	I-Protocol
line	O
can	O
be	O
fed	O
into	O
an	O
unbalanced	O
input	O
and	O
vice	O
versa	O
as	O
long	O
as	O
the	O
electronic	O
design	O
used	O
for	O
the	O
output	O
stage	O
is	O
known	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
balanced	B-Protocol
output	I-Protocol
to	O
unbalanced	O
input	O
,	O
the	O
negative	O
output	O
can	O
be	O
tied	O
to	O
ground	O
,	O
but	O
in	O
certain	O
cases	O
the	O
negative	O
output	O
should	O
be	O
left	O
disconnected	O
.	O
</s>
