Cable Wiring - Semi Symmatric

It is prefered to use balanced cables (XLR most of the time) where possible. In a balanced operation there is no signal going through the shield and noises are reduced due to phase cancelation. In an unbalanced system (90% of guitargear) the noise picked up by the shield is going to affect your signal. 

The advantage of balanced connection is that the noise picked up by the shield (that's it's function after all) doesn't interfere with the signals. A balanced cable has 2 cores, each have the same signal going through it, online one is out of phase. At the receiving end the out of phase signal is inverted again which cancels out all the noise. Great and affective method.

But not all equipement provides us with balanced cables, most only have mono in- and outputs. In that case it is wise to wire your cables Semi Symmetric. For this you would need a cable with 2 cores and one shield, a typicle mic cable. Semi Symmetric cables are wired in the following way:
Core 1: connected to both tips
Core 2: connected to both sleeves
Shield: connected only to the sleeve from the OUTPUT device (for example the preamp side for a cable that goes to a poweramp)

That way the shield works as a true shield and the 2nd core functions as a connection between ground and allows a return signal to go through without any added noise. Because the growing use of mobile phones, etc. this is a good solution to prevent hum/noise in your signal and is used in all profesional applications. It's a simple trick, but it can help a lot.