Apple Soundtrack Pro 3 - Manual (Page 519)

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.
Inverted signal
(inverted again)
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.
Combined signals
(noise eliminated)
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 applications.
Tips for Choosing Speakers and an Amplifier
Professional audio engineers have to be able to trust the sound coming from their
speakers. When you mix your audio, you need audio monitors that can handle the full
range of audio intensities and frequencies. Ideally, your monitors will have a flat frequency
response from 20 Hz to 20,000 Hz (or 20 kHz). This means that they neither attenuate nor
amplify any frequencies. Flat frequency response is important for critical listening because
the speakers themselves are not “coloring” the sound.
In addition to the speaker quality itself, additional factors affect your audio monitoring
environment:
• Size and materials of the room
519 Appendix C Working with Professional Video and Audio Equipment