XLR Balanced versus RCA Unbalanced

[DJ8077]

I know that balanced XLR is the better choice, but I'm having a difficult time trying to put my finger on the "why" - So, perhaps those with more audio knowledge than I can help fill in the blanks.

Why SHOULD one choose XLR over RCA or mini-plug for audio connections?

Thanx.

DJ

[recordingpro]

The main benefit is that any noise that gets induced into the line will be common to both the positive and negative sides and thus canceled when it arrives at its destination, assuming the destination is balanced. This phenomenon is called "Common Mode Rejection" and basically just means that any signals common to both the positive and negative legs of balanced lines get canceled. This happens because when the receiving device looks at the signal the common noise actually shows up as out of phase with itself, and gets cancelled. Think of it as if the negative (-) signal gets inverted to positive (+) before use, which puts the desired audio signal in phase with the already positive other leg and at the same time causes the undesired common noise to become out of phase with itself. Balanced lines are generally much better for long cable runs due to their ability to reject induced noises.

don't thank me for this brilliant description, the Sweetwater In Sync editor wrote this for the "word of the day" file.

hope this helps.

[david blair]

This is a great topic to revive.

I would be interested to hear from others any experience with "common mode rejection" Mic technique.
Here's my design idea.
Using two mics of similar character, one figure eight, the other cardioid, and out of phase with the first. Both wired to the same voltage source, and sent stereo to an op-amp circuit/unity gain. The output lead of the cardioid mic then routed back to the input circuit, then becoming the "difference" to be amplified for sound while the other signals are cancelled.
Will this work in a loud stage environment for an instrument pickup?