Unbalanced signals are thought of as just the “hot” signal containing the normal, or “reference,” polarity and a ground return that provides a Direct Current (DC) voltage reference. Balanced signals contain “hot” and “cold” signal lines plus the ground return. In most professional systems, the cold signal is a mirror image or an opposite polarity signal. These are NOT called in-phase and out-of-phase signals, as both signals are in-phase but opposite polarity.

Balanced signals have at least two advantages. The first is that most receiving circuitry gets twice the signal voltage amplitude (+6db), because the circuits differentially measure the signals instead of from a ground reference level. The second is that any noise added from circuit transmission to reception tends to affect both the hot and cold signal lines equally and is cancelled out. The ability for balanced signal receive circuits to reject in-phase noise signals is called “common-mode rejection.”

Figure 1 illustrates three signal plots showing signals of differing polarity or phase shift. I deliberately choose a “real world” signal type instead of nice clean sinusoidal squiggles. These unclean signals represent signal sources with a fundamental wave and other summed waves that may be harmonics or other signals that got mixed together. The point is that these signals may have non-symmetrical amplitudes, and positive and negative peaks.

To help reinforce the point, a common polarity example would be drum-head miking, where a mic placed above the head would yield an opposite polarity signal if placed below the head. Polarity switches on older guitar amplifiers also select which AC wire best represents a ground reference to the amp’s chassis. Hopefully this is an unbalanced power distro supply, with the selected wire being the neutral and a near ground reference.

Polarity switch also shows up in the channel inputs of most mixing consoles to handle the drum-head example of miking. If two mics (above and below) are used on this example, one mixer mic channel should be polarity flipped to provide a summation of the drum’s signal. Phase-shifted signal examples are easy to find in live sound environments. Anything miked in the air with different source distances enjoys that fact that acoustic waves travel at the speed of sound (nominally 366 meters per second), while electrons transit through wires at closer to 30 million meters per second. Thus electro-acoustic transducers like speakers and mics send or receive phase-shifted signals, once your ears become the reference point. This is why dual-miking, speaker arrays, and bi-amping become the focus of phase correction methods, not just polarity.

Room acoustics and reverberation are the classic example of the listener hearing the “reference” signal from the closest speaker cabinet. All other speaker cabinets and room reflections are delay versions of the reference. At best, they can be called room ambience; at worst, they decrease signal intelligibility to garble.

I wanted to comment on these phase shifting devices because while they all use similar principles, the sounds can be radically different. Phase shifters employ cascaded resistor-capacitor networks to vary the resulting time-delay, creating comb filter effects, much like having several synchronized wah-wah pedals operated at once. These comb-filter effects are the result of using the reference signal against a varying phase and amplitude effected signal. Hopefully you choose to have a phaser effect, and your sound system is not a permanent version.