Apple Final Cut Pro 6 - Manual (Page 810)

Chapter 1 Audio Fundamentals 25
I
Headroom and Distortion
If an audio signal is too strong, it will overdrive the audio circuit, causing the shape of
the signal to distort. In analog equipment, distortion increases gradually the more the
audio signal overdrives the circuit. For some audio recordings, this kind of distortion
can add a unique “warmth” to the recording that is difficult to achieve with digital
equipment. However, for audio post-production, the goal is to keep the signal clean
and undistorted.
0 dB on an analog meter refers to the ideal recording level, but there is some allowance
for stronger signals before distortion occurs. This safety margin is known as headroom,
meaning that the signal can occasionally go higher than the ideal recording level without
distorting. Having headroom is critical when recording, especially when the audio level is
very dynamic and unpredictable. Even though you can adjust the recording level while
you record, you can’t always anticipate quick, loud sounds. The extra headroom above
0 dB on the meter is there in case the audio abruptly becomes loud.
Dynamic Range and Compression
Dynamic range is the difference between the quietest and loudest sound in your mix.
A mix that contains quiet whispers and loud screams has a large dynamic range. A
recording of a constant drone such as an air conditioner or steady freeway traffic has
very little amplitude variation, so it has a small dynamic range.
You can actually see the dynamic range of an audio clip by looking at its waveform. For
example, two waveforms are shown below. The top one is a section from a well-known
piece of classical music. The bottom one is from a piece of electronic music. From the
widely varied shape of the waveform, you can tell that the classical piece has the
greater dynamic range.
Notice that the loud and soft parts of the classical piece vary more frequently, as
compared to the fairly consistent levels of the electronic music. The long, drawn-out
part of the waveform at the left end of the top piece is not silence—it’s actually a long,
low section of the music.
Waveform from a well-known
classical piece
Waveform from an excerpt of
electronic music