Apple Final Cut Express 4 - Manual (Page 609)

Chapter 41 Evaluating Levels with Audio Meters 609
VIII
Troubleshooting Audio Normalization
There are a few issues to be aware of when you use the Gain filter and the Apply
Normalization Gain command:
 Applying gain raises the level of an audio signal, including the noise. Very quiet
audio, when normalized, may be very noisy. When possible, the best solution is to
rerecord the audio.
 Loud peaks in audio clips that otherwise contain low audio levels make audio
normalization more difficult to use. For example, suppose you have a clip containing
dialogue that was recorded too quietly. At the beginning of this clip, there is a brief
peak when the slate was clapped together. When you attempt to normalize the
audio of this clip, the sound of the slate is so loud that very little gain is applied. To
apply more gain, simply trim the clip until the audio peak from the slate is gone,
then use the Apply Normalization Gain command again.
What Reference Level Should You Use for Mixing and Output?
The dynamic range of your mix is dependent on the final viewing environment. For
example, movie theaters have large, relatively expensive sound systems that can
reproduce a large dynamic range. Television speakers are much smaller, and often the
listening environment has more ambient noise, so very quiet sounds may not even be
noticeable unless the overall signal is compressed and the level increased, reducing the
dynamic range.
For example, television stations normally accommodate only 6 dB between the average
loudness and the peaks. Dolby Digital feature film soundtracks, on the other hand, can
accommodate up to 20 dB between average and peak levels. This is why loud sounds
in a movie theater sound so loud: they are much louder than the average level.
When you mix your final audio, you choose a consistent reference for the average level.
When you choose the average reference level, you are actually choosing how much
additional headroom you have before your signal distorts. The higher you set the
average level, the less safety margin you have for peaks in the signal. This means that
the loudest sounds in your mix cannot be much louder than the average levels, so the
mix is less dynamic.
Venue Acceptable amount of dynamic range
Theatrical Dolby Digital 20 dB
Average videotape 12 dB
Television broadcast 6 dB