Final Cut Pro 6 - About Balanced Audio Signals

background image

About Balanced Audio Signals

Audio cables can be either balanced or unbalanced, depending on their intended use. For
long cable runs, especially when using relatively low microphone levels, a three-wire
balanced audio circuit reduces noise. Balanced audio cables use the principle of phase
cancelation to eliminate noise while maintaining the original audio signal.

background image

Chapter 12

Connecting Professional Video and Audio Equipment



A balanced audio cable sends the same audio signal on two wires, but inverts the
phase of one signal by 180 degrees.

When noise is introduced into the cable, it is introduced equally to both the original
and the inverted signal.

When the signal arrives at its destination, the inverted signal is put back in phase and
both signals are combined. This puts the original and inverted signals back in phase,
but it causes the noise signals on each line to be out of phase.

Original signal

Inverted signal (reverse phase)

Noise on line
(affects both signals)

Inverted signal
(inverted again)

background image


Part III

Setting Up Your Editing System

Now, both audio signals are in phase, but the noise is inverted, causing the noise to be
canceled. At the same time, the original signal gets a little stronger because it is sent
on two wires and combined. This helps compensate for the reduction in signal strength
that occurs naturally on a long cable run.

Any noise introduced into the cable across its long run is almost completely eliminated
by this process.

Note: Unbalanced cables have no way of eliminating noise and are therefore not as
robust for long-distance cable runs, microphone signals, and other professional uses.