sabianq
08-30-2007, 12:50 PM
In the professional audio world,
we work with a type of signal called a "balanced" signal. you might be familiar with the XLR connection:
http://upload.wikimedia.org/wikipedia/commons/thumb/1/15/Xlr-connectors.jpg/180px-Xlr-connectors.jpg
but less known is the TRS, paradoxically widely known as a 1/4 inch stereo plug.
this stereo plug is only a stereo plug when it carries two channels of unbalanced audio. otherwise when it is used as a single channel connector in a balanced system, it is called a balanced TRS connector or 1/4 inch balanced TRS
http://www.transom.org/tools/photos/200512_microtrack/trs_plug.jpg
a common misconception is that fact that when used as a balanced connector to connect a mixer to another piece of pro-audio equipment, this plug is not a stereo plug, it is a single channel plug that is balanced.
So what is a balanced signal?
i will refer to my post in an earlier section so i don't have to retype all of this:
http://www.audioforums.com/forums/showthread.php?t=13988&page=2&highlight=balanced
the balanced cable method is a way of minimizing unwanted noise from audio signals along very long runs of cable.
the principle of Balanced audio is that two identical signals are inverted 180° out of phase will cancel each other out. balanced cables in such systems are designed to carry two versions of any given signal and are manipulated in polarity relative to each other to eliminate noise and hum.
Balanced single channel cable
http://www.mediacollege.com/audio/connection/images/2core-sh.jpg
this will make more sense when we examine unbalanced and balanced cables.
unbalanced cables not unlike balanced cables use two lines to transmit the audio signal but part of the audio signal is carried through the ground.
un-balanced single (mono) channel cable
http://www.mediacollege.com/audio/connection/images/1core-sh.jpg
unbalanced stereo (line level) cable with rca and 1/8 inch stereo plugs
http://www.kramerelectronics.com/images/cables/52.jpg
a hum can be picked up in these cables if the run is to long or if there is a difference in voltage potential on the ground of the the chassis of your equipment (this can be caused by plugging your equipment into two different power sources with a voltage draw between your common and ground)
There is a common misconception that Balanced audio equipment and cables are quieter than unbalanced equipment.
quite the contrary, as balanced equipment is great at hum rejection and is used for live "pro" applications, some of the best equipment in the world designed for mastering and audio reproduction is actually unbalanced.
The actual electronics in your Balanced equipment is actually unbalanced is just isolated from the chassis. the ground shielding of the cable provides a route for radio frequency and induction hum to get to ground without infiltrating the entire signal, any hum or RF frequency is canceled out when it propagates down the cable when it hits the other end leaving the audio signal by itself.
as you can see, there are great advantages to using balanced equipment.
for one, your pre-amps for recording are extremely sensitive to interference, induction hum and radio frequency (RF) infiltration, the use of balanced cabling eliminated that potential for radio and noise interference.
lets look at exactly how unbalanced cables work
paraphrased from this website
http://www.mediacollege.com/audio/balanced/cable-balanced.html
Balanced audio cables use three lines, they consist of a hot line (positive), cold line (negative) and earth. The audio signal is transmitted on both the hot and cold lines, but the voltage in the cold line is inverted in polarity so it is negative when the hot signal is positive. These two signals are often referred to as being 180 degrees out of phase with each other but this is not exactly correct as the signals are not delayed to be out of phase but are inverted so they are not in polarity.
http://www.mediacollege.com/audio/balanced/images/balanced-waveform.gif
When the cable is plugged into an input (on a mixer or other equipment) the hot and cold signals are combined. the signals are combined and placed back in to correct polarity and the signal becomes stronger. that is why you can run a balanced cable fro thousands of feet without signal loss.
the connectors of a balanced cable have no effect on signal quality.
there are many different types of connectors because different manufactures have different ways.
the most common are the TRS and the XLR
the TRS or commonly misidentified as the 1/4 inch stereo phono plug means (Tip Ring Sleeve) the Tip (3) and Ring (2) Carry the signal and the Sleeve (1) is the ground.
http://content.answers.com/main/content/wp/en-commons/thumb/d/de/300px-Jack_plug.png
the Mono plug or 1/4 TS connector is used in many different applications, but normally carry a signal along the ground (sleeve) (1) and the Tip (3).
The mono plug can be used to carry Speaker level signals in older PA gear but more commonly is used to carry instrument level signals like from an electric guitar to the direct box.
history of the XLR taken from
http://www.soundfirst.com/xlr.html
At one time Cannon (now ITT Cannon) made a large circular connector series that was popular for microphones called the P series. Mics used the 3 pin P3 version. Some loudspeakers use the P4 or P8 versions of this connector to this day.
In an attempt to make a smaller connector for the microphone market Cannon came out with the UA series. These were "D" shaped instead of circular and were used on such mics as the Electro-Voice 666, 666R, and 655C.
There was a desire for a smaller yet connector. Someone pointed out the small circular Cannon X series. The problem with this was it had no latch. Cannon rearranged the pins and added a latch, and the XL (X series with Latch) was born. This is the connector others such as Switchcraft and later Neutrik have copied.
Later Cannon modified the female end only to put the contacts in a Resilient Rubber compound. They called this new version the XLR series. No other company has copied this feature. It is amusing that XLR has become the generic term since what everyone else copied was the XL and not the XLR!
http://www.vandenhul.com/other/xlr-digitalL.jpg
so you can see that the connector is just a fancy way to connect equipment.
there is no difference in the audio quality of different balanced connectors.
we work with a type of signal called a "balanced" signal. you might be familiar with the XLR connection:
http://upload.wikimedia.org/wikipedia/commons/thumb/1/15/Xlr-connectors.jpg/180px-Xlr-connectors.jpg
but less known is the TRS, paradoxically widely known as a 1/4 inch stereo plug.
this stereo plug is only a stereo plug when it carries two channels of unbalanced audio. otherwise when it is used as a single channel connector in a balanced system, it is called a balanced TRS connector or 1/4 inch balanced TRS
http://www.transom.org/tools/photos/200512_microtrack/trs_plug.jpg
a common misconception is that fact that when used as a balanced connector to connect a mixer to another piece of pro-audio equipment, this plug is not a stereo plug, it is a single channel plug that is balanced.
So what is a balanced signal?
i will refer to my post in an earlier section so i don't have to retype all of this:
http://www.audioforums.com/forums/showthread.php?t=13988&page=2&highlight=balanced
the balanced cable method is a way of minimizing unwanted noise from audio signals along very long runs of cable.
the principle of Balanced audio is that two identical signals are inverted 180° out of phase will cancel each other out. balanced cables in such systems are designed to carry two versions of any given signal and are manipulated in polarity relative to each other to eliminate noise and hum.
Balanced single channel cable
http://www.mediacollege.com/audio/connection/images/2core-sh.jpg
this will make more sense when we examine unbalanced and balanced cables.
unbalanced cables not unlike balanced cables use two lines to transmit the audio signal but part of the audio signal is carried through the ground.
un-balanced single (mono) channel cable
http://www.mediacollege.com/audio/connection/images/1core-sh.jpg
unbalanced stereo (line level) cable with rca and 1/8 inch stereo plugs
http://www.kramerelectronics.com/images/cables/52.jpg
a hum can be picked up in these cables if the run is to long or if there is a difference in voltage potential on the ground of the the chassis of your equipment (this can be caused by plugging your equipment into two different power sources with a voltage draw between your common and ground)
There is a common misconception that Balanced audio equipment and cables are quieter than unbalanced equipment.
quite the contrary, as balanced equipment is great at hum rejection and is used for live "pro" applications, some of the best equipment in the world designed for mastering and audio reproduction is actually unbalanced.
The actual electronics in your Balanced equipment is actually unbalanced is just isolated from the chassis. the ground shielding of the cable provides a route for radio frequency and induction hum to get to ground without infiltrating the entire signal, any hum or RF frequency is canceled out when it propagates down the cable when it hits the other end leaving the audio signal by itself.
as you can see, there are great advantages to using balanced equipment.
for one, your pre-amps for recording are extremely sensitive to interference, induction hum and radio frequency (RF) infiltration, the use of balanced cabling eliminated that potential for radio and noise interference.
lets look at exactly how unbalanced cables work
paraphrased from this website
http://www.mediacollege.com/audio/balanced/cable-balanced.html
Balanced audio cables use three lines, they consist of a hot line (positive), cold line (negative) and earth. The audio signal is transmitted on both the hot and cold lines, but the voltage in the cold line is inverted in polarity so it is negative when the hot signal is positive. These two signals are often referred to as being 180 degrees out of phase with each other but this is not exactly correct as the signals are not delayed to be out of phase but are inverted so they are not in polarity.
http://www.mediacollege.com/audio/balanced/images/balanced-waveform.gif
When the cable is plugged into an input (on a mixer or other equipment) the hot and cold signals are combined. the signals are combined and placed back in to correct polarity and the signal becomes stronger. that is why you can run a balanced cable fro thousands of feet without signal loss.
the connectors of a balanced cable have no effect on signal quality.
there are many different types of connectors because different manufactures have different ways.
the most common are the TRS and the XLR
the TRS or commonly misidentified as the 1/4 inch stereo phono plug means (Tip Ring Sleeve) the Tip (3) and Ring (2) Carry the signal and the Sleeve (1) is the ground.
http://content.answers.com/main/content/wp/en-commons/thumb/d/de/300px-Jack_plug.png
the Mono plug or 1/4 TS connector is used in many different applications, but normally carry a signal along the ground (sleeve) (1) and the Tip (3).
The mono plug can be used to carry Speaker level signals in older PA gear but more commonly is used to carry instrument level signals like from an electric guitar to the direct box.
history of the XLR taken from
http://www.soundfirst.com/xlr.html
At one time Cannon (now ITT Cannon) made a large circular connector series that was popular for microphones called the P series. Mics used the 3 pin P3 version. Some loudspeakers use the P4 or P8 versions of this connector to this day.
In an attempt to make a smaller connector for the microphone market Cannon came out with the UA series. These were "D" shaped instead of circular and were used on such mics as the Electro-Voice 666, 666R, and 655C.
There was a desire for a smaller yet connector. Someone pointed out the small circular Cannon X series. The problem with this was it had no latch. Cannon rearranged the pins and added a latch, and the XL (X series with Latch) was born. This is the connector others such as Switchcraft and later Neutrik have copied.
Later Cannon modified the female end only to put the contacts in a Resilient Rubber compound. They called this new version the XLR series. No other company has copied this feature. It is amusing that XLR has become the generic term since what everyone else copied was the XL and not the XLR!
http://www.vandenhul.com/other/xlr-digitalL.jpg
so you can see that the connector is just a fancy way to connect equipment.
there is no difference in the audio quality of different balanced connectors.