The K-Mix has a lot of places to plug cables into and out of, and the type of cable you use can make some practical differences. I’d like to spend a little time talking about balanced, unbalanced, and differential signals, and share a few good resources with you.
A good place to start this discussion might be with the reason that these three signals (and their corresponding cables) exist in the first place, which is thanks to the invention of the difference amplifier. An ideal difference amplifier (or differential amplifier), as its name implies, amplifies or passes only the difference between two signals, while ignoring everything else they have in common.
If you think of the everyday situation of an audio signal being conveyed to an amplifier via a long single-wire conductor, like say audio coming out of an electric guitar, you’re probably familiar with the radio noise and interference that these wires can pick up – you can hear it getting amplified along with the signal when you turn up the gain. However, if you had another similar wire running in parallel to the first, with no audio but still picking up all the same radio noise and interference, you could run those two wires to a difference amplifier and cancel out all that acquired noise. Now, since you’ve already got the two conductors, you can easily double the output of the difference amplifier by running a perfectly inverted copy of your audio signal on the second conductor. Because we are subtracting one signal from the other, all noise and interference introduced in the transmission of the signal (often called Common-Mode Noise) would be cancelled and we are left with a nearly perfect copy of our original signal.
So what makes a cable balanced as opposed to unbalanced? It comes down to each signal’s relationship to ground, and to understand why, we have to look back at the way a difference amplifier works. In order to be able to cancel out the induced noise along the lines, that induced noise has to be the same on both cables. To make that happen, we want both cables to have the same resistance to ground (susceptibility to noise is directly related to this resistance). In an unbalanced line there is a conductor that is considered the signal line and another conductor that is grounded. Your standard 1/4″ guitar/instrument cable is a good example, with the TS(tip-sleeve) connection type. A balanced line has two signal conductors that have equal resistance to ground along the signal path. That is the reason for the additional conductor in TRS (tip-ring-sleeve) 1/4″ cables, or XLR cables.
Even if a signal isn’t fully differential you can still achieve good noise rejection by sending 0V into the second input of the differential amplifier. The noise will still get rejected, but you will lose the added 6 dB of gain. This is the less common balanced, non-differential signaling. Long story short, differential signaling is a great way to reduce noise from interference caused by long cables and in order to take advantage of it balanced TRS cables must be used to transfer the audio between source and destination.
There are a few good discussions floating around the internet (like HERE), and I encourage you to refer to those for a more in depth discussion. I’ll just attempt to give my quick version of all of this:
In order to take advantage of the noise cancellation properties of the differential amplifier, we need to send a signal, an inverted copy of the signal, and our ground, down one cable. When these two signals arrive at the amplifier, they will not only receive the benefits of noise cancellation, but will also double in voltage (subtracting a negative signal adds to the positive signal). This allows fully differential signals to be 6 dB louder (double the signal level) than unbalanced and non-differential balanced signals. K-Mix can accept fully differential signals at each of it’s inputs, and puts out fully differential signals at its outputs. So, although K-Mix is compatible with unbalanced signals, we recommend you use balanced cables with K-Mix whenever possible.