Tuesday, February 12, 2013

Balanced Connections, Always.

This post is part of a series on eliminating noise from audio systems. Click Here to see them all. 

Yesterday we talked about the misconceptions people have about what a power conditioner can do to get noise out of an audio system. Today we're going to look at something that's a lot more effective. Balanced connections.

In short, they use two paths for the same signal. One of the paths inverts the polarity. When those signals are combined at the input of a mixer or other piece of gear, only a signal that has a counterpart on the other conductor gets in and noise gets shut out. The science is a little deep so I'm going to skip it for the moment. Feel free to go look it up though.

The two most common kind of balanced signal connectors are the familiar XLR three pin seen on mics and the TRS 1/4" connector. The XLR has the ground on pin one, the signal on pin two and the inverted signal on pin three. With the 1/4 inch connector the tip is the signal, the ring is the inverted signal and the sleeve is the ground.

Just by making sure you only used balanced connections in your setup you can virtually eliminate noise. Out on gigs I've been in lousy situations where this has saved my life. I've had my amp racks and snake head literally on top of a pile of old SCR dimmers and had very little noise in the system.
Once everything is balanced, you then have the option of lifting the ground on an input if you do still get noise coming in. Direct boxes for electronic instruments are a great case for this. By removing the shield connection at the instrument, the cable is still draining interference off at the mixer end but there is no direct connection between the chassis of the two devices which could be hundreds of feet apart. 

One other thing that will help greatly is making sure all the audio equipment is on the same leg of the power in the building. In a lot of homes there will only be one circuit per room so it's easy. If you decide to use another room for an iso booth you should run extension cords in there to make sure any gear you plug in shares the same power. One easy way to tell if two outlets are on the same leg (even if they're different circuits) is to simply take a voltage reading. If the load is unbalanced in the building (which is usually the case) the two legs will differ by a few volts.

But all that is another discussion entirely Brethren of the Knob and Fader. So check back tomorrow.

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