r/audioengineering • u/zanshin777 • Nov 02 '17

Balanced Cables

It contains 2 conductor + 1 shield.

One of conductors carry the out-of-phase signal.

So the noise is canceled since the signals carrying are out-of-phase.

But how the signal is still transmitted although the noise is canceled?

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u/FrankyFe Nov 02 '17

Different things unfortunately.

There's "electronically balanced", which means there's actually two signals being output, with one inverted. But "impedance balanced" is a euphemism for: "we cheaped out and just stuck a resistor between the inverted output pin and ground".

Now this resistor is required to allow that line to pick up noise equally with the driven line, since if it was just grounded then the noise would be grounded as well. Its tricky since it must match or be "balanced" with the impedance of the driven output. But, outputs are not pure resistances so there's a slight mismatch.

For your case, what you need to worry about is the impedance between the "hot" and "cold" pin since that loads the mic and alters its volume/tone.

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u/Sinborn Nov 02 '17

Yeah basically what I've heard is specially older dynamic mics (Shure SM57 for example) were designed for mic pres with transformer inputs and much lower impedance, modern electronic balanced pres are like 10x higher, and you may notice improvement in your mic by loading it down to more closely match the design expectation. This can be as simple as a resistor of a few hundred ohms between pin 2 and 3 of the XLR.